The Ankle and Foot Techniques511

Introduction ●● the tibiotalar (ankle mortise) joint: is formed by articulation between the distal tibia (plafond and medial

malleolus), distal fibula (lateral malleolus) and talar dome, supported by the capsule, ligaments and tendons that cross the joint

●● the margins of the joint: are defined by the medial malleolus, the lateral malleolus, the tibial plafond and the talar dome (Figs 6.7a-c)

through the tibial plafond, represents condensation of cortical trabeculae at the normal elevation of the posterior distal tibial articular surface (Fig. 6.7d)

●● the prearticular fat pad: is found within a small fossa along the medial surface of the talar neck (Fig. 6.7b), the outer border being formed by the anterior tibiotalar ligament, and may simulate an avulsion fracture on coronal or axial images

●● ALI syndrome: is a relatively common cause of chronic lateral ankle pain after minor ankle injuries, possibly complicating ~3% of ankle sprains

●● anterolateral soft-tissue impingement: is associated with tears of the ATFL and AITFL and an accessory fascicle of the AITFL (Bassett ligament), a normal variant seen in 21-92% of individuals30

●● chronic lateral ankle instability:31 results in repetitive synovial inflammation producing a soft-tissue mass of hypertrophied synovial tissue and fibrosis (the meniscoid lesion) within the anterolateral recess of the joint: ●● the anterolateral recess: is a triangular anatomical space bounded posteromedially by the talus, laterally

by the fibula, anteriorly by the joint capsule and ATFL, superiorly by the AITFL and inferiorly by the calcaneofibular ligament (CFL) (Fig. 6.8a)

●● less commonly, ALI may be seen following surgery (e.g. for talar dome osteochondral repair) with associated capsular scarring or arthrofibrosis

●● anterolateral bony impingement:28 typically relates to bony spurs arising from the anterolateral margin of the tibial plafond, inferior to the attachment of the joint capsule: ●● spurs in this location are commonly seen in athletes and are likely to reflect repetitive impaction ●● impingement symptoms may arise due to entrapment of the adjacent anterior joint capsule

●● clinically: ALI presents with focal anterolateral pain and tenderness exacerbated by dorsiflexion and eversion ●● MR findings:

●● conventional MRI:32 demonstrates soft-tissue thickening in the anterolateral gutter, which is of low SI on T1W images and low/intermediate SI on PDW/T2W images, optimally seen on axial images between the AITFL and ATFL (Fig. 6.8b):

● however, this is not a specific finding, also being seen in asymptomatic individuals ● a low SI ‘meniscoid’ mass within the anterolateral gutter of the ankle joint, optimally visualised on

axial and coronal images in the presence of fluid within the lateral gutter (Fig. 6.8c) ●● associated features include:

● a soft-tissue mass within the medial gutter of the tibiotalar joint (50%) ● abnormality (tear, thickening) of the ATFL (100%) and CFL (50%) ● less commonly, anterolateral tibial plafond osseous spurs (Figs 6.8d, e) and loose bodies ● subtle chondral defects along the anterolateral talar dome are sometimes associated with osseous spurs

and may be orientated in the sagittal plane (‘tram-track’ chondral lesions) ● talar dome subchondral bone bruising

●● arthrofibrosis: appears as thickening of the anterior capsule (≥3 mm) (Figs 6.8f, g), which is typically of intermediate SI on PDW images during the first 6 months following surgery, but progressively of lower SI over time33

●● the sensitivity and specificity of conventional MRI ranges from 30-100%, but improves in the presence of an ankle effusion

●● the optimal demonstration of pathology is with direct MR arthrography,11,34 while indirect MR arthrography has not proven to be of additional value35

●● AI syndrome: is a relatively common cause of chronic ankle pain, being particularly seen in athletes applying repeated dorsiflexion stress on the ankle, such as footballers and ballet dancers37

●● pathologically: it is associated with a beak-like bony prominence from the anterior margin of the tibial plafond and a corresponding osteophyte from the dorsum of the talus, proximal to the talar neck and within the joint capsule, with impingement of the soft tissues between the 2 osteophytes in dorsiflexion

●● however, the presence of anterior spur formation without capsular or soft-tissue impingement is also commonly seen in asymptomatic athletes

●● MRI findings: ●● anterior tibial and dorsal talar osteophytes, which may show marrow oedema (Figs 6.9a, b) with

synovitis in the anterior capsular recess of the joint (Fig. 6.9c) ●● associated cartilage lesions are described in ~81%, with the extent of osteophyte formation correlating

with the severity of chondral damage (Figs 6.9a, b)38

●● AMI syndrome: is an uncommon cause of chronic ankle pain, limitation of ankle dorsiflexion or a snapping sensation on dorsiflexion due to pathology in the anteromedial recess: ●● the anteromedial recess: is an anatomical space bounded posteriorly by the medial malleolus, laterally

by the anteromedial aspect of the talar dome, body and neck and anteriorly by the joint capsule (Fig. 6.10a)

●● pathologically: AMI results from formation of a ‘meniscoid’ lesion of thickened soft tissues along the anteromedial recess of the joint, which may arise in isolation or be associated with a partially torn deep deltoid ligament: ●● it may also occur secondary to a thickened anterior tibiotalar ligament ●● the thickened soft tissue impinges on the anteromedial corner of the talus during dorsiflexion, resulting in

formation of an osteophyte and/or a chondral lesion ●● very rarely, an intra-articular plica mimicking a loose body may be observed at the anteromedial recess

and give rise to impingement39 ●● bony spurs arising along the anteromedial tibial plafond or dorsomedial aspect of the talar neck may also

give rise to symptoms of anteromedial impingement, the spur formation being secondary to repetitive impaction in certain sports, including football

●● AMI syndrome: is often associated with medial or lateral collateral ligament injury ●● MRI findings:

●● conventional MRI may miss the capsular or soft-tissue thickening along the anteromedial recess unless a joint effusion is present (Figs 6.10b, c)

●● bony spurs with marrow oedema along the dorsomedial talar neck and anteromedial rim of the tibial plafond may be present, which are best visualised on sagittal images (Figs 6.10d, e)

●● pericapsular oedema situated along the anteromedial aspect of the joint (Fig. 6.10e) ●● thickening and oedema of the anterior tibiotalar portion of the deltoid ligament, usually best seen on

sagittal and coronal images ●● bone marrow oedema may be seen within the medial talar body/neck (Fig. 6.10f) and medial malleolus

(medial ‘kissing contusions’) ●● an anteromedial plica (Figs 6.10g, h)

●● a medial ‘meniscoid’ lesion, with irregular thickening of the soft tissues anterior to the tibiotalar ligament and medial malleolus

●● thickened anterior tibiotalar ligament and associated talar chondro-osseous injury

●● POMI syndrome: is an uncommon cause of chronic posteromedial ankle pain ●● pathologically: it follows a severe inversion injury with crushing of the deep posterior fibres of the deltoid

ligament between the medial wall of the talus and the medial malleolus: ●● POMI is associated with lateral ligament disruption, and often becomes symptomatic once the lateral

ligament injury has been successfully treated ●● inadequate healing of the posterior deltoid ligament results in chronic inflammation and soft-tissue

hypertrophy within the posteromedial recess, with resulting impingement between the medial malleolus and talus

●● the posteromedial recess: is a small anatomical space bounded anteriorly by the medial malleolus and posterior tibiotalar ligament, posteriorly by the posteromedial joint capsule and medially by the posteromedial border of the talar dome/body and posteromedial talar process: ●● the recess is best demonstrated on axial images, located deep to the interval between FDL and FHL

tendons (Fig. 6.11a) ●● MRI findings:42

●● hyperintensity, enlargement and loss of the normal striated pattern of the posterior deltoid ligament, appearing as soft-tissue thickening between the medial malleolus and talar dome (Figs 6.11b, c)

●● partial encasement of the tibialis posterior tendon (TPT), FDL and FHL tendons by the hypertrophied mass (Fig. 6.11c)

●● marrow oedema (‘kissing contusions’) of the medial talus and adjacent medial malleolus (Fig. 6.11d) ●● associated features include: abnormality of the lateral ligaments (Fig. 6.11c), thickening of the

posteromedial capsule, posterior/posterolateral synovitis and concurrent injury to the flexor retinaculum43 ●● posteromedial process avulsion fracture of the talus

●● PI syndrome: refers to a group of abnormalities that result from repetitive or acute plantar flexion of the foot, and is classically seen in ballet dancers: ●● less commonly, PI may be seen following an acute traumatic hyperflexion injury

●● PI syndrome: is also referred to as os trigonum syndrome, talar compression syndrome and posterior block of the ankle

●● pathologically: the posterior process of the talus or os trigonum and adjacent soft tissues become compressed between the posterior tibial margin and calcaneus, with several osseous variants predisposing to the condition, including: ●● os trigonum: an accessory ossicle of the lateral process of the talus that persists into adulthood in

approximately 7% of individuals (Figs 6.12a, b) ●● a ‘Stieda’ process: an elongated lateral process of the talus (Figs 6.12c, d) ●● a downward sloping posterior lip of the talus (Fig. 6.12e)

●● pseudarthrosis of the lateral talar tubercle (Fig. 6.12f) ●● a prominent posterior process of the calcaneus ●● loose bodies within the posterior capsular recess (Fig. 6.12g)

●● soft tissue causes of impingement: include the posterior intermalleolar ligament (PIML) and scarring of the PTFL or PITFL: ●● the PIML is a normal variant of posterior ankle ligament anatomy, that extends from the superior margin

of the malleolar fossa of the distal fibula to the posterior margin of the medial malleolus ●● it lies between the PITFL and inferior transverse ligament above, and the PTFL below (Figs 6.13a, b),

being identified in 19% of subjects on MRI and up to 82% of cadaveric specimens, measuring ~4 cm in length and 4 × 3 mm in width and thickness, respectively45,46

●● the ligament may have multiple bundles medially, usually combining to form a single cord laterally, and occasionally projecting anteriorly between the tibia and talus to resemble a meniscus

●● it may become trapped between the tibia and talus during ankle plantar flexion, resulting in fraying and bucket-handle tears causing PI47

●● more rarely PI may occur in the presence of a displaced tear of the CFL ●● soft-tissue changes associated with PI include:

●● synovitis of the FHL tendon sheath and of the posterior synovial recesses of the tibiotalar and posterior subtalar joints

●● marrow oedema in the lateral talar tubercle and/or the os trigonum (Figs 6.14a, b): ● hyperintensity may also be observed along the margins of the synchondrosis, indicating a degree of

stress, although this finding is not specific for PI, while fluid SI across the synchondrosis is indicative of destabilisation (Fig. 6.14c)

●● fragmentation of the lateral talar tubercle and/or os trigonum ●● synovitis in the posterior soft tissues, including:

● the FHL tendon sheath (Fig. 6.14d), the posterior synovial recesses of the tibiotalar and posterior subtalar joints, although the presence of fluid distension alone without synovial thickening is not specific for PI (Fig. 6.14c)

●● a thickened PIML (Fig. 6.14e), and a thickened PTFL, which may be hyperintense (consistent with myxoid change) (Fig. 6.14b) with or without ganglion formation

●● chondral lesions: are common in the ankle joint, producing non-specific symptoms, including persistent ankle pain and subjective instability

●● MRI grading of cartilage lesions: ●● grade 1: abnormal intrachondral SI with smooth outline ●● grade 2: mild surface irregularity with/without focal defect <50% depth of the cartilage

●● grade 3: severe surface irregularity with cartilage loss >50% depth but not full-thickness ●● grade 4: full-thickness cartilage loss with denuded subchondral bone

●● MR arthrography: has a reported accuracy of ~90% for the detection of cartilage lesions of the tibia, fibula and talus49

●● MRI findings: ●● higher grade focal defects can be demonstrated with conventional MR images (Figs 6.15a, b) ●● displaced chondral fragments may occasionally be seen along the anterior or posterior joint recesses ●● occult cartilage fissures may manifest as marrow oedema (Fig. 6.15c), only being identified on either CT

(Fig. 6.15d) or MR arthrography

●● intraosseous ganglia: are relatively uncommon lesions of unknown aetiology, but may be post-traumatic ●● of 75 cases reported in the literature, 55 involved the medial malleolus (Figs 6.16a-c), 9 the lateral malleolus

and 11 the talus (Figs 6.16d, e)51 ●● clinically: they occur in middle-aged patients (median age 44 years; age range 14-86 years), presenting with

mechanical ankle pain and, commonly, no abnormal physical findings ●● MRI findings:

●● subchondral cystic lesions with intermediate SI on T1W (Figs 6.16a, d) and high SI on PDW/T2W/ STIR (Figs 6.16b, c, e), and a thin sclerotic margin (Fig. 6.16d)

●● may have associated marrow oedema (Fig. 6.16b), fluid levels (Fig. 6.16e) and joint effusion

●● the lateral collateral ligament (LCL) complex: consists of 3 components, the anterior talofibular ligament (ATFL), the posterior talofibular ligament (PTFL) and the calcaneofibular ligament (CFL)

●● the ATFL: extends between the anterior aspect of the lateral malleolus (Fig. 6.17a) to the talar neck, just anterior to the fibular articular surface: ●● it is optimally demonstrated on axial MR images as a thin, hypointense band running between the lateral

malleolus and talar body (Fig. 6.17b) ●● fluid within the anterolateral recess of the joint highlights the ligament on T2W images ●● it may normally appear bi-fasciculated or striated with mild increased intraligamentous SI on PDW/T2W

images57

●● PTFL: has a broad, fan-shaped origin from the fibular fossa of the distal fibula and attaches to the posterior aspect of the distal tibia, being the strongest component of the LCL: ●● it is demonstrated on axial and coronal images (Figs 6.17b, c), appearing striated due to the presence of

interspersed fat ●● it may normally demonstrate marked heterogeneity and thickening

●● the CFL: runs between the tip of the lateral malleolus (Fig. 6.17a) to a small tubercle on the lateral aspect of the calcaneus (Fig. 6.17d): ●● it is demonstrated on coronal, axial and sagittal images (Fig. 6.17e), being identified as an intermediate

SI band deep to the peroneal tendons and often incompletely visualised on axial images due to its oblique orientation

●● however, improved visualisation of the CFL may be achieved by the use of multi-planar reconstruction (MPR) from standard 2D turbo spin echo MR images,58 or by the use of an oblique coronal plane planned perpendicular to the posterior subtalar joint (Figs 6.17f, g)59

●● MR arthrography:9 injected contrast medium can outline both the superficial and deep surfaces of the ATFL and PTFL (Figs 6.2c, d) and also optimises demonstration of the deep surface of the CFL

●● inversion injuries: represent ~85% of ankle sprains and involve the lateral ligaments, with lateral ankle sprains representing 16-21% of all sports related ankle injuries

●● the ATFL: is the weakest ligament and is therefore the first torn, being typically followed by the CFL and finally the PTFL, although isolated tears of the CFL or PTFL are rarely reported61

●● the classification of ankle sprains is based on the number of affected ligaments: ●● 1st degree sprain: partial or complete tear of the ATFL ●● 2nd degree sprain: partial or complete tear of the ATFL and CFL ●● 3rd degree sprain: injury to ATFL, CFL and PTFL

●● MRI findings: ●● morphological abnormality: including discontinuity (Fig. 6.18a), detachment, without or with bony

avulsion (Fig. 6.18b), thickening (Figs 6.18c-e) or thinning and irregularity (Fig. 6.18f) ●● SI changes: within and around the ligament including heterogeneity and increased SI on PDW/T2W

images (Figs 6.18a-e) ●● utilising these criteria, MRI has a reported accuracy of up to 100% for acute ATFL injuries60 ●● the use of supplementary coronal oblique views along the long axis of the CFL significantly improves the

sensitivity of CFL tears from ~35% to >85%59 ●● associated features: include obliteration of fat planes around the ligament and extravasation of joint fluid

(Fig. 6.18a): ● CFL tears: may be associated with fluid in the peroneal tendon sheath ● bone bruises:62 are reported in ~17% of patients suffering a lateral ligament injury and most

commonly involve the medial talus or occasionally the lateral talus and calcaneus, typically, resolving spontaneously within 6-12 months (Figs 6.18g, h)63

●● chronic tears: show morphological abnormality without the associated soft tissue and bone SI changes seen with acute injuries (Figs 6.18c-e):

● however, chronic tears may also be associated with reduced SI in the surrounding fat due to scarring or synovial proliferation

● MRI has a reported accuracy of 93% for chronic ATFL injuries,60 92% for chronic partial CFL tears and 96% for chronic complete CFL tears64

●● MR arthrography is more sensitive and accurate than conventional MRI for the diagnosis of lateral ligament injury

●● non-visualisation of the ligament or extension of contrast medium anterior to the ATFL is indicative of a tear (Fig. 6.19a), while CFL tear is associated with extension of contrast medium into the peroneal tendon sheath (Fig. 6.19b)

●● extension of contrast into the soft-tissues posterior to the PTFL indicates a tear

●● the medial collateral ligament (MCL) complex: is also termed the deltoid ligament and consists of 5 components, separated into deep and superficial layers

●● the deep layer comprises: ●● the anterior tibiotalar ligament (ATTL), which runs anteriorly from the tip of the medial malleolus to

the talar neck, being seen as a thin band on axial images (Fig. 6.20a), but does not always exist ●● the posterior tibiotalar ligament (PTTL), a thick structure that extends between the tip of the medial

malleolus to the medial talar surface and consists of multiple fascicles due to the presence of interposed fatty tissue, being demonstrated on coronal, axial and sagittal images and typically having a striated pattern (Figs 6.20b-d)

●● the deep layer of the deltoid ligament is intra-articular and surrounded by synovium ●● the superficial layer: comprises 3 ligaments that all arise from the tip of the medial malleolus:

●● the tibiocalcaneal ligament (TCL), which extends to the sustentaculum tali, running deep to the tibialis posterior and FDL tendons and being optimally visualised on coronal images (Fig. 6.20e)

●● the tibionavicular ligament (TNL): which runs anteriorly to the medial navicular tuberosity and seen as a thin band on axial images (Fig. 6.20f)

●● injury to the deltoid ligament: particularly the tibiotalar component is associated with inversion injuries (lateral ligament sprains), syndesmotic injuries or a fibular fracture (especially Weber type B fractures)

●● isolated deltoid ligament injuries: account for ~5% of all ankle sprains and may follow an eversion-lateral rotation injury mechanism

●● tears of the superficial layer of the deltoid ligament:67 appear to be more common than deep tears at surgery, although they may be missed at MRI as they are often quite subtle: ●● surgically proven tears of the superficial deltoid typically involve the superior fibre attachment, with or

without involvement of the mid-substance or distal fibres ●● surgically confirmed tears of the deep deltoid typically involve the mid-substance, although a co-existing

superficial deltoid tear may also be seen in >90% ●● inversion sprains: may cause partial tears of the PTTL due to crushing between the medial wall of the talus

and medial malleolus, which may progress to POMI syndrome ●● MRI findings:

●● loss of the regular striations normally seen in the deltoid ligament (Figs 6.21a, b) ●● homogeneous intermediate SI on T1W images and increased SI on FS T2W/STIR images (Fig. 6.21a) ●● superficial deltoid ligament tears:67 typically involve the superior attachment fibres (Fig. 6.21c) and may

extend from anterior to posterior as slender, focal fluid SI best seen on axial images (Fig. 6.21d) ●● high-grade deltoid ligament injuries manifest as diffuse increased SI on T2W images with fluid-filled gaps

(Fig. 6.21e) or complete disruption ●● MRI has a reported sensitivity and specificity for superficial deltoid tears of 83% and ~94%, respectively,

● effusion within the tibialis posterior tendon sheath ● medial malleolar or distal avulsion fractures (Fig. 6.21f) ● concurrent injuries to the syndesmotic ligaments, spring ligament complex or talar dome

●● MR arthrography: may improve visualisation of partial-thickness tears of the deep aspect of the deltoid ligament11

●● the Achilles tendon: originates in the mid-calf as the combined tendons of the medial and lateral heads of gastrocnemius and the soleus muscle, and functions to flex the foot

●● as the tendon descends, the fibres rotate laterally approximately 90° such that the gastrocnemius fibres insert laterally and the soleus fibres insert medially into the marrow of the posterosuperior margin of the calcaneus, this insertion being an enthesis

●● the tendon dimensions are approximately 10-15 cm (length) × 5-7 mm (thickness) × 12-16 mm (width) ●● it lacks a true tendon sheath but has a paratenon laterally and posteriorly, composed of visceral and parietal

layers whose vascular system extends both within and outside the tendon ●● the tendon is relatively avascular 2-6 cm proximal to the calcaneal insertion, accounting for the increased

prevalence of tears at this site ●● on sagittal MR images: the anterior and posterior margins of the tendon are parallel below the soleus

insertion (Figs 6.22a, b) ●● on axial MR images:

●● just above the soleus insertion, the anterior margin is typically straight or convex ●● at the soleus insertion, the anterior margin is typically convex and may be focally bulbous (Fig. 6.22c),

while below the soleus insertion the anterior margin of the tendon is concave (Fig. 6.22d)

●● small punctate areas of increased SI may be seen in the distal tendon due to inter-fascicular membranes (Fig. 6.22d)

●● at the calcaneal enthesis, the tendon is flat and spans the whole width of the bone (Fig. 6.22e) ●● on coronal MR images: the sides of the tendon are straight and the tendon widens distally (Fig. 6.22f) ●● the tendon is typically hypointense on all pulse sequences (Figs 6.22a, b), although internal longitudinal,

linear increased SI on T1W/PDW images may be seen, due to the normal fascicular anatomy of the tendon: ●● such striation should be less prominent or not visible on T2W images

●● increased T1W/PDW intratendon SI may also be due to the ‘magic angle’ phenomenon (Fig. 6.22g), resulting from the normal twisting of fibres within the tendon

●● the plantaris tendon: lies medial to the Achilles tendon (Figs 6.23a, b) and may become confluent with the Achilles tendon (~20%), inserting onto the medial aspect of the superior calcaneal tuberosity or ~1 cm anteromedial to the Achilles tendon insertion (Figs 6.23a, c): ●● it is absent in 6-8% of individuals,71 and is occasionally hypertrophied (Figs 6.23d, e)

●● the retrocalcaneal (pre-Achilles) bursa: a true anatomical bursa lying between the distal Achilles tendon and the adjacent calcaneus, and is normally visible on MRI but should measure <6 mm craniocaudally, <3 mm transversely and <2 mm anteroposteriorly (Fig. 6.23f)

●● the retro-Achilles bursa: an acquired or adventitial bursa lying between the posterior distal tendon and the skin, and is not normally visible

●● Kager’s fat pad: a triangular fat pad lying anterior to the Achilles tendon and posterior to the distal tibia (Figs 6.23g, h), and containing multiple hypointense strands due to vessels

●● the fascia cruris: is the fascial layer enveloping all the posterior muscles/tendons of the calf (Fig. 6.23h), and merges with the Achilles paratenon (Fig. 6.23i)

●● Achilles tendon injuries: may be classified as insertional (~25%) and non-insertional (~75%) ●● insertional injuries:70 include insertional tendinosis, which is possibly associated with the Haglund deformity

of the calcaneus, being an overuse injury commonly seen in runners: ●● it may be associated with an enthesophyte, a bony outgrowth at the inferior aspect of the tendon insertion

and may be complicated by a distal tear ●● an association with inflammatory arthropathy is also recognised, in which retrocalcaneal and retro-

Achilles bursitis may be present ●● inflammatory changes in the presence of a Haglund deformity are collectively referred to as Haglund

syndrome:81 ● predisposing factors include hindfoot varus and pes cavus

●● ossification at the Achilles tendon insertion: is believed to represent endochondral ossification of the enthesis and is typically age-related rather than necessarily indicative of inflammation or tendinopathy

●● ossification of the distal Achilles tendon: separate from the enthesis, may relate to prior or on-going injury/inflammation

●● non-insertional injuries include: ●● diffuse acute and chronic paratenonitis (paratendinitis):

● isolated paratenonitis, in the presence of a normal Achilles tendon, is typically seen in young athletic individuals, commonly runners

● chronic paratenonitis: may lead to paratenon vessel proliferation and hypoxic Achilles tendinopathy ● paratenonitis may also be observed in RA, although in such cases it is often asymptomatic82

●● tendinosis/tendinopathy: of which several forms are described, including hypoxic degenerative, mucoid, lipoid and calcifying

●● hypoxic degenerative tendinopathy: is the most common type and presents with gradual intermittent pain and focal swelling, with the abnormal tendon being predisposed to acute tear

●● mucoid degeneration: is commonly asymptomatic apart from focal swelling and also predisposes to tear, at which time it may become symptomatic

●● lipoid degeneration: results in fatty deposits within the tendon but does not appear to predispose to tears, but may be related to tendon xanthoma formation (see below)

●● calcifying tendinopathy: is a rare sequela of tendon injury occurring in ~3% of torn Achilles tendons and may progress to tendon ossification

●● rupture/tears: may be partial or complete, typically occurring 2-6 cm proximal to the calcaneal insertion and most commonly seen in middle-aged males, performing infrequent sporting activities, mainly associated with running:

● ruptures more commonly affect the left Achilles tendon, and predisposing conditions include RA, gout and DM as well as certain drugs, such as steroids and fluoroquinolones

● rarely, tears may be distal, complicating insertional tendinosis or proximal, at the musculotendinous junction and typically involving the medial head of gastrocnemius

●● MRI findings: ●● insertional tendinosis: increased SI and swelling at the insertion site of the tendon (Figs 6.24a-c),

with/without intrasubstance calcification or ossification (Fig. 6.24d): ● distension/thickening of the retrocalcaneal bursa and the presence of any amount of fluid within

the retro-Achilles bursa (Fig. 6.24c) ● marrow oedema within the posterosuperior calcaneal eminence is seen in ~25% of cases (Fig. 6.24e)83 ● Haglund deformity: a reactive enlargement of the posterior calcaneal tuberosity assessed on a sagittal

image using the method of parallel pitch lines (Fig. 6.24f) ● patients with a Haglund deformity have a greater prevalence of retrocalcaneal bursitis (90% vs. 34%)

and insertional Achilles tendinosis (47% vs. 10%) than patients without the deformity ●● paratenonitis: high T2W SI rim around the Achilles tendon (Figs 6.25a, b) with linear or irregular SI

changes in the pre-Achilles fat pad: ● increased T2W SI indicates oedema, while reduced SI on all sequences indicates scarring of the paratenon ● the Achilles tendon may be normal, particularly in acute paratenonitis, but Achilles tendinosis often

coexists ●● chronic tendinosis/tendinopathy:70

● hypoxic degenerative tendinopathy: fusiform thickening of the tendon 4-6 cm proximal to its insertion as seen on sagittal images (Figs 6.25c, d), the tendon assuming an oval configuration on axial images (Fig. 6.25e) with loss of the normal concave anterior contour and little or no intratendinous SI change on T2W images

● mucoid degeneration: tendon swelling with increased intrasubstance SI on T1W, PDW and T2W images (Fig. 6.25f) with or without longitudinal interstitial tearing

●● partial tears: heterogeneous SI within the tendon due to haemorrhage and tendon swelling with focal fibre fraying, but without complete discontinuity (Fig. 6.26a):

● associated features: subcutaneous oedema and haemorrhage within Kager’s fat pad ●● complete tears: complete tendon discontinuity with fraying and retraction of the tendon ends:

● in acute rupture: the tendon gap is filled with haemorrhage and oedema, manifesting intermediate SI on T1W and high SI on PDW/T2W/STIR images (Figs 6.26b, c)

● the identification of musculotendinous junction ruptures requires the use of an extended FOV (Figs 6.26d, e)

● in chronic rupture: the tendon gap is filled with scar tissue (Fig. 6.26f) or fat ● associated features: include muscle atrophy, which occurs first in the soleus muscle and rarely affects

gastrocnemius ●● additional findings with Achilles tendon abnormalities:

● calcaneal enthesophyte (Fig. 6.26g), which may show marrow oedema ● degenerative cyst within the calcaneus at the inferior most aspect of the tendon insertion ● occasionally, extensive calcaneal oedema anterior to the tendon insertion (Fig. 6.26h)

●● acute tears of the fascia cruris: along the medial or lateral margin of the paratenon have been described in high level athletes as a cause of swelling and pain along the upper/mid-portion of the Achilles tendon, utilising ultrasound for diagnosis

●● MRI findings: thickening and oedema of the fascia, corresponding to findings at ultrasound (Figs 6.27a, b)

●● plantaris tendon injury: includes strain and rupture, and both can clinically mimic an Achilles tendon injury or even DVT: ●● rupture of the plantaris may occur in association with a strain of the medial head of gastrocnemius and/or

soleus and is sometimes referred to as ‘tennis leg’

●● MRI findings: ●● plantaris strain: increased SI within and adjacent to the plantaris fibres on T2W images ●● plantaris rupture: typically occurs at the myotendinous junction with associated muscle retraction, and

may appear as a hyperintense mass on T2W images between the medial head of gastrocnemius and soleus muscles

●● tendon xanthoma: is a manifestation of types I-III hyperlipoproteinaemia, which are inherited abnormalities of lipid metabolism

●● the Achilles tendon: is the most commonly involved, with the disorder usually resulting in non-tender, bilateral tendon enlargement, typically presenting in the early 3rd decade of life, and simultaneous involvement of other ankle tendons is also well-recognised

●● tendon xanthomas: do not appear to predispose to tendon rupture, and with treatment of systemic hyperlipidaemia, the abnormal tendon appearances may regress88

●● MRI findings: ●● marked, fusiform enlargement of the tendon (Figs 6.28a, b) ●● heterogeneous globular areas of mildly increased T1W and T2W SI due to xanthomatous deposits

(Fig. 6.28c), which often enhance after administration of gadolinium, with interspersed low SI trabecular SI due to residual normal tendon fibres (Fig. 6.28d)

●● the tibialis posterior muscle: acts to plantar flex the ankle and invert the foot, and during normal gait the tibialis posterior tendon (TPT) stabilises the longitudinal arch of the foot at the talonavicular and calcaneocuboid joints

●● the TPT: forms in the distal third of the lower limb and lies adjacent to the posteromedial tibia in the distal calf, and at the level of the ankle joint the tendon lies in a posteromedial groove of the distal tibia, medial to the FDL and FHL tendons: ●● on axial images (Fig. 6.29a): the normal TPT is approximately 2× the size of the FDL and FHL tendons,

slightly smaller than the tibialis anterior tendon and slightly smaller than the combined size of the peroneal tendons

●● the tendon then curves around the medial malleolus, deep to the flexor retinaculum where it runs within the tarsal tunnel, being optimally demonstrated on axial oblique (Fig. 6.29b) and coronal (Fig. 6.29c) images

●● the tendon insertion:91,92 is complex, mainly into the navicular tuberosity or an accessory navicular, which is present in up to 28% of the population, the insertion is optimally demonstrated on sagittal (Fig. 6.29d) and axial (Fig. 6.29e) images: ●● smaller slips insert into the cuneiforms (Figs 6.29d, f ), cuboid and bases of the 2nd-4th metatarsals

(Fig. 6.29f) ●● the normal tendon: is hypointense on all pulse sequences, although heterogeneous increased SI on low TE

sequences (<37 ms) may be seen in the distal 2-3 cm of the tendon due to magic angle effect (Fig. 6.29g), particularly when imaged with the foot at 90° to the lower leg: ●● such increased SI disappears with the tendon imaged in the prone position93 ●● enlargement and heterogeneity of the tendon insertion into the navicular tuberosity may be seen on

T1W images (Fig. 6.29h) due to interposed connective/fibrocartilaginous tissue and partial volume averaging of the adjacent spring ligament and tibionavicular and tibiotalar components of the deltoid ligament

●● a small amount of fluid can be normally seen within the tendon sheath, but since the tendon sheath ends at mid-talar level, fluid around the distal 1-2 cm is abnormal

●● TPT disorders: include a spectrum of pathology ranging from tenosynovitis and tendinosis, to partial and complete tendon rupture

●● clinical findings: include foot pain, weakness, gait disturbance with/without progressive foot deformity ●● acute tenosynovitis: is typically an overuse injury seen in young athletes, but may also be encountered in

inflammatory arthritides including RA, seronegative arthropathy, gout and SLE ●● tendon tears: either acute partial or complete, are uncommon and usually a result of a sporting injury, with

the tear typically occurring at the insertion into the navicular ●● chronic TPT rupture: is typically seen in women in the 5th-6th decades and is associated with progressive flat

foot deformity: ●● contributing factors include DM, inflammatory arthropathy, obesity and steroid use ●● tears are commonly identified immediately distal (intrasynovial ‘critical zone’) or posterior to the medial

malleolus and are classified into 3 types: ● type 1: partial tear with fusiform enlargement, intrasubstance degeneration and longitudinal splits ● type 2: elongation and stretching of the tendon ● type 3: complete tear

●● TPT dysfunction: puts excessive stress on the sinus tarsi ligaments and the spring ligament, which may result in worsening of the flat foot deformity and an increase in pain

●● TPT dislocation: is a rare post-traumatic condition typically seen in young individuals, usually following a severe dorsiflexion injury with rupture of the flexor retinaculum

●● paratendinosis: may be the first manifestation of TPT dysfunction, where the tendon sheath is not present distally: ●● extrasynovial tendon dysfunction may be seen in young athletic individuals and also in inflammatory

arthropathies ●● MRI findings:

●● acute tenosynovitis: effusion in the tendon sheath measuring >2 mm with a normal morphology of the tendon (Figs 6.30a, b)

●● chronic tenosynovitis: scarring of the paratenon (Figs 6.30c, d) with nodular or diffuse swelling of the tendon

●● tendinosis: swelling of the tendon with mild-to-severe heterogeneity of SI (Figs 6.30e, f ), and heterogeneous enhancement following contrast (Fig. 6.30g)

●● paratendinosis: increased T2W/STIR SI around the distal tendon (Figs 6.30h, i) ●● chronic tears:

● type 1: on axial images, the tendon may be 5-10 times the diameter of the adjacent FDL tendon (Fig. 6.31a), with internal high SI foci due to longitudinal splits (Fig. 6.31b), the imaging features being similar to chronic tendinosis

● type 2: on axial images, the tendon appears atrophied but without alteration of SI, the tendon calibre being equal to or less than the FDL (Fig. 6.31c)

● type 3: complete discontinuity of the tendon fibres (Fig. 6.31d), with the tendon gap filled by either fluid or scar tissue

●● associated features of TPT pathology include: ● an accessory or cornuate navicular (see later) ● sinus tarsi syndrome:97,98 which is reported in 72% of patients with advanced TPT insufficiency, while

47% of patients with sinus tarsi syndrome are reported to have TPT insufficiency ● spring ligament injury:98 which is reported in 92% of patients with advanced TPT insufficiency,

typically affecting the superomedial fibres of the spring ligament (see below) ● periostitis: at the insertion of the flexor retinaculum on the distal tibia ● focal marrow oedema:99 which is usually present in the posteromedial subcortical area of the tibia/

medial malleolus, adjacent to the tendon (Fig. 6.31e) and less commonly in the talus and navicular (Fig. 6.31f), being more commonly seen in the setting of inflammatory arthropathy

●● TPT subluxation/dislocation: is optimally demonstrated on axial images, with the tendon identified medial or anterior to the medial malleolus:

● it may be associated with a shallow retromalleolar groove

●● TPT dysfunction: can result in adult flat foot deformity, with hindfoot (calcaneo-) valgus, talar flexion and lateral navicular subluxation

●● extra-articular impingement: is a cause of lateral ankle pain occurring between the anterior fibula and sinus tarsi in patients with severe flat foot and hindfoot valgus, and may be due to: ●● talocalcaneal impingement: occurring between the lateral talus and calcaneus ●● subfibular impingement: occurring between the lateral malleolus and lateral calcaneus ●● with progressive deformity, secondary OA of the subtalar, talonavicular and calcaneocuboid joints may

develop and contribute to pain ●● MRI findings:

●● hindfoot valgus: may be measured on coronal images as the angle between lines drawn along the length of the tibia and calcaneus, and should be between 0 and 6°,with >6° indicating hindfoot valgus (Fig. 6.32a):

● however, this measurement is made in the non-weight bearing position

●● talonavicular malalignment: plantar flexion of the talus, diagnosed on sagittal images at the level of the first metatarsal base when a line drawn along the mid-talus passes through the inferior aspect of the navicular (Fig. 6.32b)

●● lateral subluxation of the navicular: diagnosed on axial images when less than 85% of the distal talar articular surface is covered by the navicular (Fig. 6.32c)

●● talocalcaneal impingement: cystic changes, sclerosis and oedema in the posterior subtalar joint, the lateral process of the talus and the lateral calcaneus (Figs 6.32d, e)

●● subfibular impingement: extensive lateral soft-tissue thickening and oedema between the fibula and the calcaneus with entrapment of the CFL (Fig. 6.32f), fibular tip marrow oedema/cysts (Fig. 6.32g) and contact between the fibula and calcaneus occasionally with the formation of a pseudarthrosis:

● peroneal tendon subluxation may be seen (Fig. 6.32h)100

●● the FDL tendon: runs around the medial malleolus (Fig. 6.33a) together with the TPT, from which it is separated by a thin fibrous septum (Figs 6.29a-c)

●● in the sole of the foot: the tendon turns laterally and passes superficial to the FHL (Figs 6.33b, c) at the knot of Henry before inserting into the plantar aspect of the bases of the distal phalanges of the 2nd-5th toes

●● the FDL tendon: lies within its own synovial sheath and tendon sheath fluid is seen proximally in 25% of normal individuals: ●● the FDL and FHL tendon sheaths typically communicate at the knot of Henry, which can result in a small

amount of FDL tenosynovial fluid (Fig. 6.33b) especially in the presence of severe FHL tenosynovitis or a large ankle joint effusion

●● injury to the FDL tendon and/or isolated FDL tenosynovitis are rare (Fig. 6.33d)

●● the FHL tendon: begins just above the level of the medial malleolus (Figs 6.34a, b), and at the level of the ankle joint the tendon lies lateral to the TPT and FDL tendons (Fig. 6.29a), being well demonstrated in all 3 planes

●● the FHL tendon: runs within a synovial sheath lined fibro-osseous tunnel deep to the flexor retinaculum, and bounded by the medial and lateral talar tubercles, entering the foot by crossing the posterior subtalar joint and passing under the sustentaculum tali (Figs 6.29c and 6.34b)

●● it inserts into the plantar aspect of the base of the distal phalanx of the great toe, after passing deep to the FDL tendon at the knot of Henry (Figs 6.33b, c)

●● the tendon appears hypointense on all sequences, although it is subject to magic angle effect distal to the medial malleolus (Fig. 6.34b) when the ankle is imaged in the supine position93

●● a small amount of fluid is commonly seen in the tendon sheath, since this communicates with the ankle joint in 20% of individuals (Fig. 6.34c)

●● injury of the FHL tendon: is uncommon compared with Achilles tendon, TPT and peroneal tendon pathology, but usually occurs as it passes through the fibro-osseous tunnel formed by the medial and lateral talar tubercles: ●● repetitive friction results in chronic/stenosing tenosynovitis, tendinosis and partial/complete tears, and

may be predisposed to by a low-lying muscle belly (Fig. 6.35a) ●● less common sites of injury include the passage through the sesamoids, at the knot of Henry and below

the sustentaculum tali ●● reported causes include:

●● os trigonum (most common), resulting in posterior impingement syndrome ●● an old calcaneal fracture, or old fractures of the posterior malleolus or medial malleolus

●● FHL tendon pathology: is classically described in ballet dancers from chronic, repetitive plantar flexion stress

●● MRI findings: ●● chronic tenosynovitis: manifests as fluid around the intact tendon in the absence of a significant ankle joint

effusion (Figs 6.35b, c), whereas in the presence of a large joint effusion, FHL tendon sheath fluid is most likely due to normal communication with the joint and is of no clinical significance

●● tenosynovitis at the sustentaculum/knot of Henry (Figs 6.35d, e) ●● stenosing tenosynovitis: appears as extensive scarring around the tendon sheath and may result in

functional hallux rigidus ●● tendinosis and partial tear: manifests as tendon swelling and intrasubstance increased SI ●● FHL tendon entrapment: is suggested by the finding of abrupt cut-off of tendon sheath effusion at the level

of the posterior talus (Fig. 6.35b)

●● the peroneus brevis tendon (PBT): forms in the distal calf and passes around the lateral malleolus to insert onto a tuberosity on the lateral aspect of the base of the 5th metatarsal (Fig. 6.36a)

●● the peroneus longus tendon (PLT): forms in the distal calf and passes posterior and lateral to the PBT around the lateral malleolus (Figs 6.36a, b)

●● the PBT and PLT: share a common synovial sheath that begins approximately 4 cm above the lateral malleolus and extends to the calcaneocuboid joint

●● at the ankle, both tendons run within a fibro-osseous tunnel posterior to the lateral malleolus called the retromalleolar groove (RMG), and within the groove the PBT typically lies anteromedial to the PLT (Fig. 6.36b): ●● on axial images at the RMG, the PBT is usually flat (Fig. 6.36c) or mildly crescentic (Fig. 6.36d), and

rarely is bifurcated, while the PLT is usually oval (Figs 6.36c, d) ●● the normal PBT and PLT are smaller than, or equal in size to the TPT at the same axial level

●● the tendons are stabilised within the groove by the superior peroneal retinaculum (SPR) and CFL ●● the SPR:104 forms the posterolateral border of the retromalleolar groove, comprising a fibrous band

originating from the posterior ridge of the distal fibula and inserting into the lateral wall of the calcaneus (Fig. 6.36e), or rarely attaching to the Achilles tendon: ●● it has a mean thickness is ~1 mm and at the attachment to the fibular periosteum, a triangular

fibrocartilage is frequently observed, which serves to deepen the RMG (Fig. 6.36f) ●● distally, the tendons are stabilised by the inferior peroneal retinaculum (IPR) (Fig. 6.36g) ●● at the level of the calcaneus, the tendons run superficial to the CFL (Fig. 6.17g) ●● the PLT then turns medially to run within the cuboid tunnel, deep to the cuboid bone (Fig. 6.36h) to insert

into the plantar surface of the lateral cuneiform and base of the 1st metatarsal (Fig. 6.36i) ●● both muscles act to produce plantar flexion and eversion of the ankle/foot, although the primary function of

PLT is plantar flexion of the 1st ray of the foot

●● the RMG: is smooth and concave in 82% of individuals (Fig. 6.37a), flat in 11% (Fig. 6.37b) and convex in 7% (Fig. 6.37c); the latter 2 configurations predisposing to lateral subluxation and tears of the PBT and PLT: ●● the groove may also be irregular in contour, again predisposing to tears

●● pseudosubluxation of the PBT: is present when the tendon lies medial to the medial edge of the RMG (Fig. 6.37d), a feature that can be accentuated by supination of the foot

●● low-lying peroneus brevis muscle: which is defined as extension of muscle tissue distal to the RMG (Fig. 6.37d) and may predispose to peroneal tendon and SPR tears secondary to overcrowding: ●● it is a common anatomic variant, reported in ~88% of subjects with symptomatic tendon pathology,

but also ~54% of control subjects106 and may be a normal finding with the ankle imaged in dorsiflexion ●● enlarged protuberances of the lateral calcaneal wall:

●● the peroneal tubercle:107,108 which is present in ~40% of individuals and separates the PBT and PLT (Fig. 6.38a):

● hypertrophy may irritate the PLT, predisposing to tenosynovitis, tear and formation of an adventitial bursa (Fig. 6.38b), and hypertrophy ≥4.3 mm is associated with a 73% sensitivity and 74% specificity for the presence of partial tears

●● the retrotrochlear eminence: which is seen in 98% of individuals and is located posterior to the peroneal tubercle and tendons (Fig. 6.38c):

● hypertrophy is often associated with an accessory peroneus quartus muscle ●● os peroneum:26,109 represents a sesamoid bone within the PLT:

●● an ossified os peroneum is present in 3-26% of the population and it may be bipartite (Fig. 6.38d) or multipartite in 25-30% of cases

●● it usually occurs in the region of the calcaneocuboid joint (Figs 6.38e, f ) and rarely on the plantar side of the cuboid with which it may articulate (Fig. 6.38g), appearing as a focal area of marrow or cartilage SI within the tendon

●● it may be symptomatic due to fracture or diastasis of a multipartite os, or in association with peroneus longus tendinopathy/tear (‘painful os peroneum syndrome’), which manifests on MRI as oedema in and around the os (Fig. 6.38h)

●● proximal migration of the os is a sign of complete PLT rupture

●● accessory peroneal muscles: have a prevalence of ~16% and include the peroneus quartus (commonest), peroneus-calcaneus externum, peroneus accessorius, peroneus digiti minimi and peroneus digiti quinti

●● the peroneus quartus muscle: has a reported prevalence of 12-22% in cadaver studies and originates at the distal lateral fibula, descending posteromedial to the peroneal tendons (Figs 6.39a, b): ●● it has a variable site of insertion, including the retrotrochlear eminence of the calcaneus, the 5th metatarsal,

the peroneal tendons (Fig. 6.39c), the lateral retinaculum or the cuboid bone ●● occasionally, the muscle inserts directly onto the calcaneus (Fig. 6.39d) ●● the muscle is usually asymptomatic, but may cause crowding of the structures in the RMG, predisposing

to PBT subluxation, tears and tenosynovitis111 ●● the peroneus digiti minimi: has a reported prevalence of ~15-34% and originates from the peroneus

brevis: ●● the muscle is invariably asymptomatic and forms two tendons, one inserting onto the proximal phalanx of

the 5th toe and the other onto the base of the 5th metatarsal ●● the peroneus accessorius: is of unknown prevalence and originates from the peroneus brevis muscle:

●● it typically inserts onto the peroneus longus, does not abut the neurovascular bundle and is not usually associated with any symptoms

●● peroneal tendon injuries: include peritendinitis, tenosynovitis, tendinosis and rupture ●● peritendinitis and tenosynovitis: are thought to be due to increased stress at the RMG, peroneal tubercle or

the under surface of the cuboid bone: ●● they also occur secondary to ankle inversion injuries, lateral malleolar and calcaneal fractures

●● acute tenosynovitis: is typically seen in athletes and ballet dancers, presenting with swelling and tenderness over the lateral aspect of the ankle and foot

●● stenosing tenosynovitis: occurs when synovial hypertrophy and fibrosis occur around the tendon, limiting its mobility: ●● it may be associated with hypertrophy of the peroneal tubercle114

●● tendinosis: is a chronic overuse injury developing over several months and resulting in minimal swelling and tenderness: ●● it may be a precursor to longitudinal splits of the PBT and is also associated with systemic conditions such

as RA, seronegative arthropathy and DM ●● it is also closely associated with lateral ligament injury

●● PBT rupture: may be acute or chronic: ●● acute tears: occur in young, athletic individuals due to overuse injury ●● chronic tears: occur in older patients as a degenerative phenomenon, and may be asymptomatic

●● chronic longitudinal PBT tears (peroneal splits):115 usually originate within the fibular groove due to trapping of the tendon between the PLT and the lateral malleolus, and may be associated with rupture of the peroneal retinaculum or inversion injury: ●● clinical symptoms: include pain, swelling, instability and occasionally clicking or popping along the

posterolateral ankle ●● PLT rupture: may be associated with one-third of PBT tears at the level of the lateral malleolus, but

more commonly occurs in isolation at the level of the peroneal tubercle of the calcaneus, or in the cuboid tunnel: ●● it is related to sports injury or calcaneal fracture/calcaneocuboid joint injury ●● PLT rupture also occurs in the midfoot, in the region of the cuboid tunnel,116 resulting in

posterolateral foot pain or pain along the plantar surface of the foot, possibly with a previous history of trauma

●● PBT or PLT injury: may occur in association with osteochondral or chondral injury of the talus, typically in the context of ankle instability and chronic pain: ●● 65% of patients with talar dome lesions have concomitant peroneal tendon pathology, including

tenosynovitis and/or tears117 ●● tendon subluxation/dislocation: may be clinically misdiagnosed as an ankle sprain:

●● acute dislocation occurs due to sudden foot dorsiflexion with violent contraction of the peroneal muscles, and results in detachment of the SPR allowing lateral dislocation of the tendons from the RMG

●● chronic dislocation is associated with chronic ankle instability and laxity of the SPR ●● MRI findings:

●● peritendinitis: manifests as scarring around the tendons (Figs 6.40a, b), fluid within the tendon sheath with normal tendon morphology, and enhancement of the abnormal soft tissue following contrast (Fig. 6.40c)

●● tenosynovitis: is diagnosed if fluid completely surrounds the tendons and is greater than 2 mm in diameter or 25% the width of the tendon (Figs 6.40d, e)

● however, tendon sheath effusion may also be a sign of CFL tear ● rarely, marrow oedema may be seen in the lateral calcaneus

●● stenosing tenosynovitis: manifests as thickened synovium/scar tissue around the tendon and linear strands of low SI within the tendon sheath effusion (Figs 6.40f, g)

●● tendinosis/tendinopathy:113 appears as enlargement and/or increased T2W SI with/without tendon sheath effusion:

● although a relatively insensitive finding for tendinopathy, the individual peroneal tendons should be considered enlarged if they are equal to or larger than the TPT on the same axial image (Figs 6.41a, b)

● increased SI within the tendon (Fig. 6.41c) on 3 consecutive axial PDW images has the highest sensitivity (92%) in detecting symptomatic tendinopathy

●● PBT rupture:115 appears C-shaped on axial MR images with the ruptured tendon partially enveloping the PLT (Figs 6.41d, e):

● partial or full-substance splits may be seen and intrasubstance increased SI is present on both T1W/ PDW and T2W images

● complete tendon rupture manifests as tendon discontinuity (Fig. 6.41f) and an empty tendon sheath filled with haemorrhage or scar tissue depending upon the age of the rupture (Fig. 6.41g)

● MRI has a reported sensitivity and specificity of 83% and 75%, respectively, for detection of PBT tears118

● associated features: include a shallow or convex RMG in 95% of patients: – a traction spur at the lateral aspect of the lateral malleolus in 70% of patients – PBT subluxation, PLT tear and a peroneus quartus muscle/tendon – injury to the lateral ligaments and marrow oedema in the lateral malleolus99

●● PLT tears:116 partial or complete disruption manifests as morphological and SI changes within the tendon, either at the level of the peroneal tubercle (Figs 6.42a, b) or the cuboid:

● midfoot tears: are optimally assessed on coronal oblique images perpendicular to the metatarsals, complete tears manifest as an empty tendon sheath at the cuboid tunnel and proximal and distal retraction of the ruptured tendon ends (Figs 6.42a, c): – fluid may also be seen in the tendon sheath (Fig. 6.42c)

● associated features include: marrow oedema in the lateral calcaneus and/or a hypertrophied peroneal tubercle99 (Fig. 6.42d)

● marrow oedema within the cuboid119 (Figs 6.42e, f ) may be seen with midfoot PL tendinopathy/ tenosynovitis

●● subluxation/dislocation: is best demonstrated on axial images, where the tendons are identified anterolateral to the lateral malleolus (Figs 6.43a, b):

● the displaced tendons may be surrounded by a ‘pouch’ of soft tissue representing the torn SPR (type 1 injury of the SPR; see below)

● associated features include:120 tenosynovitis or tendon tears, a convex RMG, an accessory peroneal muscle (~15%), avulsion fracture of the distal fibula, and a tear of the lateral collateral ligament

● ‘dynamic’ MRI: may be of value in demonstrating peroneal tendon subluxation121

●● SPR injury: occurs due to sudden foot dorsiflexion with forceful contraction of the peroneal muscles, resulting in elevation of its periosteal attachment: ●● it has been described in skiing, ice skating, rugby and gymnastics ●● lateral ankle ligament injuries are frequently seen in association with SPR dysfunction (78% of cases),

typically occurring following inversion injury with resulting SPR laxity122 ●● classification of SPR injury:

●● type 1: periosteal stripping at the SPR attachment on the lateral malleolus ●● type 2: SPR tear at its distal fibular attachment ●● type 3: distal fibular avulsion fracture at the SPR attachment ●● type 4: SPR tear at its posterior attachment (least common)

●● unrecognised SPR injuries are associated with an increased risk of longitudinal tears of the peroneal tendons due to chronic repetitive friction

●● MRI findings: ●● retinacular thickening demonstrated on T1W and T2W images, typical for type 2 injuries (Fig 6.43c) ●● avulsion fracture of the fibular attachment of the SPR with mild marrow oedema within the distal fibula ●● soft-tissue oedema around the SPR on T2W/STIR images ●● peroneal tendon subluxation/dislocation is often seen (see above)

●● the tibialis anterior tendon (TAT): is the medial-most extensor tendon, located at the front of the ankle (Figs 6.44a, b), where it is stabilised by the superior and inferior extensor retinacula

●● the tendon sheath: forms several centimetres proximal to the joint, and unlike the flexor tendons of the ankle, the TAT sheath does not usually contain fluid and even a small amount should be considered abnormal

●● the tendon insertion: is into the anteromedial aspect of the medial cuneiform (Fig. 6.44c) and the inferomedial aspect of the 1st metatarsal base (Fig. 6.44d), with insertion into both occurring in 84-96% of individuals (Fig. 6.44d): ●● since there is no tendon sheath at the insertion site, any fluid along the distal tendon is abnormal

●● on axial MR images at the ankle joint, the TAT is round or oval with a short axis diameter of 5 mm or less (Fig. 6.44a), becoming flatter distally (Fig. 6.44e)

●● increased tendon SI on short TE sequences may be present in 20% of cases due to magic angle effect when imaged in the supine position with the ankle neutral

●● a longitudinal split of the tendon just prior to its insertion is normal (Fig. 6.44f)

●● the superior extensor retinaculum (SER): covers the TAT in the distal lower limb and at the ankle joint, is a transverse aponeurosis with lateral attachment to the lower fibula and lateral malleolus (Figs 6.45a, b) and medial attachment to the distal tibia and medial malleolus (Figs 6.45a, b): ●● laterally, it is continuous with the superficial peroneal retinaculum and medially with the flexor retinaculum ●● the 3 extensor tendons pass deep to the retinaculum, but in 25% of cases there is a separate tunnel formed

by superficial and deep layers for the TAT (Fig. 6.45b) ●● the inferior extensor retinaculum (IER): is a Y-or X-shaped structure located over the dorsum of the foot

and ankle and composed of 4 components; the stem (frondiform ligament), the oblique superomedial limb, the oblique inferomedial limb and the oblique superolateral limb: ●● the stem: originates laterally from 3 roots (lateral, intermediate and medial) arising in the sinus tarsi

(Fig. 6.45c) and stabilises the EDL tendon (Fig. 6.45d) and peroneus tertius muscle against the talus and calcaneus, bifurcating medially into the 2 oblique medial limbs

●● the oblique superomedial limb: inserts into the anterior aspect of the medial malleolus, passing over the EHL tendon and TAT

●● the oblique inferomedial limb: extends inferomedially from the stem to insert into the calcaneonavicular joint at the medial border of the foot

●● the oblique superolateral limb: is present in 25% of cases

●● injury to the TAT: is uncommon since it is subject to little mechanical stress because of its relatively straight course

●● it may undergo both hypoxic degenerative tendinosis or mucoid degeneration, which may lead to partial or complete closed tendon tears: ●● closed tears: are uncommon due to the rich vascularity of the tendon and usually occur at the level of

the IER, 2-4 cm from the distal insertion where there is a zone of relative tendon hypovascularity ●● 82% occur at the level of the cuneonavicular joint and medial cuneiform128

●● open tears: due to laceration may be relatively asymptomatic since foot dorsiflexion can be maintained by the other extensor tendons: ●● they may present with a mass on the dorsum of the foot due to the retracted tendon stump

●● clinically: chronic TAT injury presents most commonly in women in the 6th-7th decades with swelling at the dorsomedial aspect of the midfoot and slight foot drop, being predisposed to by inflammatory arthritis, DM, infection, ischaemia, gout, obesity, hyperparathyroidism, SLE and steroid therapy: ●● chronic TAT injury: at the level of the SER may also occur as an overuse injury in young athletic

individuals undertaking hill running or hiking ●● acute TAT tears: are less common and occur at any age due to massive trauma, such as laceration or

fracture ●● MRI findings:

●● tenosynovitis: manifests as even a small amount of tendon sheath fluid with normal tendon morphology (Fig. 6.46a)

●● tendinosis:123,128 results in tendon swelling (Figs 6.46b, c): ● a short axis diameter of >5 mm has a sensitivity and specificity of 94% and 98% for differentiating

normal from tendinosis or partial tear ● SI abnormality in the deep portion (39%), diffusely (54%) or the superficial portion (7%) of

the tendon ● associated features include dorsal osteophytes from the navicular or medial tarsometatarsal joint,

possibly resulting in mechanical irritation ●● peritendinosis: manifests as soft-tissue swelling/oedema around the distal insertion, where there is no

tendon sheath, which is best assessed on the most medial sagittal image (Fig. 6.46d) or the most distal axial image (Fig. 6.46e)

●● spontaneous tendon rupture: the most common sites are its insertion into the medial cuneiform, beneath the oblique superior limb of the IER, and in a triangular space between the 2 oblique limbs of the IER

●● TAT tears: appear as increased T2W SI (Fig. 6.46f), with complete tears showing a focal segment of fluid-filled empty tendon sheath:

● tendon retraction occurs with complete tears, resulting in a palpable mass either at the level of the SER (Figs 6.46g, h) or the oblique superomedial limb of the IER

● swelling and enhancement of the oblique superomedial limb of the IER may also be seen124 – associated findings:123 seen in symptomatic individuals include marrow oedema-like SI changes

at the tendon insertion, dorsal osteophytes from the medial tarsometatarsal joint, a bony spur contacting the tendon from the navicular surface, and a ridged medial surface to the medial cuneiform bone

●● at the level of the ankle, the extensor hallucis longus (EHL) lies medial to the extensor digitorum longus (EDL), separated by the anterior tibial artery (Fig. 6.44a)

●● the EHL tendon: inserts into the dorsal surface of the base of the great toe distal phalanx: ●● increased EHL tendon SI on short TE sequences may be present due to magic angle effect when imaged in

the supine position with the ankle neutral

●● the EDL tendon: splits into 5 separate tendons inserting into the dorsal surfaces of the bases of the 2nd-5th distal phalanges and into the lateral aspect of the shaft of the 5th metatarsal

●● the peroneus tertius muscle:129 represents an inconsistent lateral slip of the EDL muscle (absent in ~18% of individuals) (Fig. 6.47), arising from the distal third of the anterior surface of the fibula, adjacent interosseous membrane and anterior intermuscular septum: ●● its tendon runs with the EDL tendon under the extensor retinaculum and inserts into the dorsum of the

base of the 5th metatarsal

●● acute injury: to the EHL and EDL tendons (Figs 6.48a, b) is less common than to the TAT ●● the EHL and EDL tendons: are superficial and may therefore be torn by deep laceration to the dorsum of the foot ●● overuse injuries: including closed tendon ruptures are rare and invariably associated with a predisposing

cause, including inflammatory arthritides, infection, DM or midfoot arthropathy: ●● tenosynovitis (Fig. 6.48c) and chronic tendinopathy (Fig. 6.48d) may be seen ●● overuse injuries have also rarely been described in certain sports, including ultra-marathon and martial arts130

●● extensor retinacular injury: is typically described with forced dorsiflexion trauma to the foot and may result in a complete or partial tear, with or without an avulsion fracture

●● MRI findings: ●● retinacular thickening and heterogeneity on T1W and fluid sensitive sequences ●● surrounding soft-tissue oedema, and discontinuity observed with complete rupture

●● the accessory soleus muscle: has a reported prevalence of 0.7-5.5% in cadaveric studies, being twice as common in males and rarely bilateral

●● it originates from the anterior surface of the soleus muscle or from the soleal line of the tibia or fibula and has a variable insertion, with 4 common types described: ●● a tendinous insertion: into the upper surface of the calcaneus ●● a muscular insertion: into the Achilles tendon, or into the upper or medial surface of the calcaneus

●● clinically: it presents in adolescence/young adulthood as a painful lower calf mass, the pain commonly being exercise induced, or rarely may present with a traumatic injury:133 ●● symptoms may be due to nerve compression, exercise induced claudication or compartment syndrome

●● MRI findings: ●● the muscle is optimally assessed on sagittal (Fig. 6.49a) and axial (Fig. 6.49b) images, appearing as a

fusiform mass with SI characteristics of muscle, lying deep to the Achilles tendon but outside the tarsal tunnel and superficial to the flexor retinaculum

●● insertion sites are as described above (Figs 6.49c, d), and if the muscle is particularly large, it can compress the posterior tibial neurovascular bundle anteriorly against the tibia

●● the accessory soleus can be differentiated from a low lying soleus muscle, since the latter inserts normally into the Achilles tendon (Fig. 6.49e), as opposed to the calcaneus

●● the TCI muscle: is a rarely reported accessory muscle, which originates from the medial tibial crest and inserts on the medial calcaneus, usually 1-2 cm anterior to the insertion of the Achilles tendon

●● it passes inside the tarsal tunnel, deep to the flexor retinaculum (distinguishing it from an accessory soleus) and may give rise to symptoms of tarsal tunnel syndrome: ●● its location within the tarsal tunnel may resemble a flexor digitorum accessories longus muscle (see below),

but the TCI insertion does not extend into the quadratus plantae (Fig. 6.50), helping to distinguish these accessory muscles

●● the FDAL muscle: has a reported prevalence of 2-8% in cadaveric studies, is rarely bilateral and possibly more common in males

●● the muscle has a variable origin in the lower leg, including the FHL muscle, the flexor retinaculum, soleus, tibia and fibula

●● FDAL: runs posterior to the FHL muscle within the tarsal tunnel, and remains mainly muscular as it travels through the tunnel, becoming tendinous just prior to exiting the tunnel

●● the tendon: joins the FDL tendon in the midfoot, before the latter splits into its 4 terminal tendons ●● clinically: the accessory muscle is usually asymptomatic but may be a cause of tarsal tunnel syndrome ●● MRI findings:

●● optimally visualised on axial images as a muscular structure deep to the flexor retinaculum and posteromedial to the FHL muscle/tendon (Fig. 6.51a)

●● within the tarsal tunnel, it runs behind the posterior tibial nerve (Figs 6.51b, c), and after exiting the tunnel, its tendon runs within quadratus plantae (Fig. 6.51b), into which it may insert

●● it may also insert into the FDL tendon, but this is difficult to visualise

●● the PCI muscle: has a reported prevalence of 1% in asymptomatic individuals and is frequently bilateral ●● it originates from the distal fibula, beneath the origin of the FHL tendon, and its tendon runs with the FHL

tendon under the sustentaculum tali to insert into the calcaneus ●● there are no reported cases of a symptomatic PCI muscle ●● MRI findings:

●● the muscle belly of PCI (Figs 6.52a, b) interdigitates with FHL and tapers as it approaches the tibiotalar joint (Fig. 6.52a)

●● the tendon runs posterolateral to the FHL tendon beneath the sustentaculum and inserts into a small tubercle on the medial surface of the anterior calcaneus (Fig. 6.52c)

●● the foot: may be divided into the hindfoot, midfoot and forefoot ●● the hindfoot consists of:

●● bones: talus and calcaneus ●● joints: the subtalar joint ●● associated anatomy: the sinus tarsi, plantar fascia and tarsal tunnel ●● it is separated from the midfoot at Chopart’s (mid-tarsal) joint comprising: the talocalcaneonavicular joint

supported by the spring ligament complex, and the calcaneocuboid joint ●● the midfoot consists of:

●● bones: the navicular, cuboid and cuneiforms (medial, intermediate and lateral) ●● joints: the cuneonavicular, the intercuneiform, the cuneocuboid and the cuboid-navicular joints ●● associated muscles and tendons ●● it is separated from the forefoot at the Lisfranc (tarso-metatarsal) joint comprising: the metatarso-

cuneiform joints and the metatarso-cuboid joint ●● the forefoot consists of:

●● bones: the metatarsals and phalanges ●● joints: the metatarsophalangeal and interphalangeal joints ●● associated muscles and tendons

●● the talus: is formed of a head, neck and body: ●● the talar head: extends distally, having a convex articular surface for articulation with the navicular and

inferiorly with the sustentaculum tali (Fig. 6.53a) ●● the talar neck: lies just posterior to the head and is slightly narrowed, having an inferior deep groove called

the sulcus tali, which forms the roof of the sinus tarsi (Fig. 6.53b) ●● the talar body: is cuboidal, with its superior surface (the talar dome) articulating with the tibial plafond

(Fig. 6.53b), its lateral surface articulating with the lateral malleolus, its medial surface articulating with the medial malleolus (Fig. 6.53c), and its posterior margin having 2 small tubercles (lateral and medial) between which is a groove for the FHL tendon (Fig. 6.53d)

●● pseudodefects of the talus:26 posterior and central pseudodefects of the talus are described on MRI: ●● the posterior pseudodefect: is demonstrated on lateral parasagittal images and is related to a normal groove

for the PTFL (Fig. 6.54a), being identified in 96% of ankle MRI studies: ● it may be mistaken for an articular erosion or osteochondral defect

●● the central pseudodefect:136 represents a crescentic area of low SI on medial parasagittal images at the level of the sustentaculum tali and is reported to be present in ~60% of ankle MR studies:

● it is located either centrally (Fig. 6.54b) or at the junction of the central and posterior thirds (Fig. 6.54c) of the talus, measures ~11 × 4 mm in size and lies 2-4 mm deep to the surface of the talar dome

● it represents partial volume imaging through a region of cortical thickening at the insertion of the deltoid ligament (Fig. 6.54d)

●● the calcaneus: is the largest of the foot bones, having 6 surfaces: ●● the anterior surface: articulates with the cuboid (Fig. 6.55a) ●● the posterior surface: forms the heel and gives attachment to the Achilles tendon (Fig. 6.55a)

●● the superior surface: has 2 articulations with the talus, separated by a groove, the sulcus calcanei, which forms the floor of the sinus tarsi (Fig. 6.55b)

●● the inferior surface: has anterior, medial and lateral tubercles, which provided attachment sites for the plantar aponeurosis

●● the medial surface: has a large projection termed the sustentaculum tali (Figs 6.55c, d) ●● the lateral surface: is almost flat but has 2 elevations, the peroneal tubercle and the retrotrochlear

eminence, related to the peroneal tendons (Figs 6.38a, c) ●● anatomical variants of the calcaneus:26

● os sustentaculi: represents a rare accessory ossification centre located at the posterior end of the sustentaculum tali, being reported in less than 1% of the population: – it is the ossified remnant of a talocalcaneal union normally present in embryonic life and is attached

to the calcaneus by fibrous/fibrocartilaginous tissue – it may be identified on coronal and axial MR images as a marrow filled ossicle attached to the

sustentaculum via an irregular low SI (fibrous) line and should not be mistaken for a fracture ● pseudocyst of the calcaneus: is caused by a paucity of trabeculae within the anterior aspect of the

calcaneus and appears on MRI as a focal area of increased fat SI (Fig. 6.55e)

●● the subtalar (talocalcaneal) joint: is formed from 3 facets (posterior, middle and anterior), 2 hyaline cartilage covered articulations and the sinus tarsi (Figs 6.56a-e)

●● OLT: is the preferred terminology although the condition is also referred to as osteochondritis dissecans (OCD) and osteochondral defect

●● OLT: represent ~1% of talar fractures and complicate ~6.5% of ankle sprains, although they may be missed on initial radiographs17,142

●● an associated ligament injury is found in 28-45% of cases,142 while peroneal tendon pathology is present in ~65% of cases117

●● commonest sites: ●● the middle third of the lateral border (45% of cases) (Figs 6.57a, b): occurring secondary to inversion

injury with dorsiflexion of the foot and commonly associated with lateral ligament injury: ● resulting lesions typically appear thin and shallow, with the width of the surface fragment being greater

than the depth (Figs 6.57a, b) ●● the posterior third of the medial border (55% of cases) (Figs 6.57c, d): occurring secondary to inversion

injury with plantar flexion of the foot and lateral rotation of the tibia on the talus: ● such lesions tend to have a deeper, crater-like appearance (Figs 6.57c, d)

●● clinically: there is commonly a history of acute trauma or of pain unresponsive to treatment for a previous ankle injury

●● MRI classification: ●● stage 1: involve the subchondral bone with intact overlying cartilage ●● stage 2: involve subchondral bone with partial detachment of overlying cartilage:

● stage 2a: associated subchondral cyst formation ●● stage 3: completely detached osteocartilaginous fragment that is still in-situ ●● stage 4: displaced detached osteocartilaginous fragment (loose body)

●● MRI can demonstrate:143 the size and location of the lesion, the status of the overlying articular cartilage, the congruity of the articular surface, the viability of the bone fragment, the stability of the lesion and the location of a displaced fragment within the joint

●● MRI findings: ●● stage 1 lesion: focal subchondral hypointensity on T1W/PDW (Fig. 6.58a) and hyperintensity on FS

T2W FSE/STIR (Fig. 6.58b) with normal overlying cartilage ●● stage 2 lesion: focal subchondral hypointensity on T1W and hyperintensity on T2W/STIR with partial

tear of the overlying cartilage (Fig. 6.58c): ● the presence of a subchondral cyst indicates stage 2a (Figs 6.58d, e)

●● stage 3 lesion: a completely separated osteocartilaginous fragment within its site of origin (Fig. 6.58f) ●● stage 4 lesion: an osseous defect in the talar dome with a loose intra-articular osteocartilaginous fragment

(Fig. 6.58g) ●● assessment of lesion stability is made on T2W images:

● a hypointense interface between the fragment and underlying bone suggests stability (Fig. 6.58h) ● a high SI interface isointense to fluid between the fragment and underlying bone indicates instability

(Fig. 6.58f) ● hyperintensity at the interface, which does not reach the SI of fluid may indicate vascular granulation

tissue with the potential for healing

● the presence of surrounding oedema also suggests at least partial instability (Figs 6.58d, f, h) ● with direct gadolinium MR arthrography: instability is diagnosed if injected contrast passes between

the fragment and the underlying bone ●● assessment of fragment viability:

● low SI of the fragment on all pulse sequences indicates a necrotic fragment (Fig. 6.58f) ● hyperintensity of the fragment on T1W images indicates that the fragment is viable, while

enhancement of the fragment on post-contrast FS T1W images also indicates viability

●● the MR appearances of a conservatively treated OLT can change with time:142 ● in a study of 29 lesions followed for a mean of 13.7 months, 45% of lesions showed progression,

24% had improved, while 31% remained essentially stable: – minimally symptomatic lesions do not appear to progress or worsen over time144

● MRI may show changes in lesion size, progression or resolution of subchondral cyst formation and marrow oedema (Figs 6.58h, i), and also changes in SI at the interface of the lesion and host bone, which may indicate the presence of either healing or loosening

●● bone contusions/bone bruises (BB): are associated with ligament injuries, usually the lateral ligaments and typically involve the medial talus and medial malleolus, or occasionally the calcaneus: ●● BB has been reported in 27% of acute ankle inversion injuries, and a complete tear of the ATFL is

observed in ~92% of patients with medial joint line BB, which is thought to represent a ‘contrecoup’ impaction injury in the context of acute ankle inversion147

●● bone bruising in the talar dome is considered equivalent to stage 1 OLT (Figs 6.59a, b) (see above) ●● MRI findings:

●● reticular/ill-defined areas of reduced marrow SI on T1W and hyperintensity on FS T2W/STIR (Figs 6.18g, h)

●● they represent microfracture and marrow oedema/haemorrhage, being seen acutely and lasting for 2-3 months

●● stress injuries: represent a continuum from stress reactions (which include microfractures) to complete fractures ●● stress fractures: the calcaneus is the second commonest site of stress fracture in the foot, following the

metatarsals ●● calcaneal stress fractures: typically occur as fatigue fractures in athletes involved in running/jumping,

or insufficiency fractures in the setting of RA, neurological disorders and osteoporosis: ●● they usually involve the posterosuperior/posterior aspect of the calcaneus with a vertical/oblique

orientation (Figs 6.60a, b) ●● a specific insufficiency avulsion fracture of the posterior calcaneal tuberosity has been described in diabetics ●● clinically: they present with diffuse heel pain and tenderness on the lateral and medial sides

●● stress injuries of the talus:151,152 are uncommon, being described mainly in military recruits and less commonly in athletes, or as insufficiency fractures with osteoporosis/RA/steroid usage: ●● military recruits: 67% involve the talar head (usually the upper part – 75%), 25% the body (usually the upper

part – ~60%) and 8% involve the posterior talus (Figs 6.60c, d), usually in association with an os trigonum ●● stress fractures of the lateral tubercle of the posterior process of the talus are rare, but may be seen in

footballers and ballet dancers due to repetitive extreme plantar flexion153

●● stress injury of adjacent bones is also common, the navicular in 50% of cases and the calcaneus in ~30% ●● a hypointense fracture line is present in 18% of cases

●● talar stress injuries: are potentially at higher risk for complete fracture or non-union than those of the calcaneus, and typically require longer immobilisation and more aggressive conservative management77,154

●● MRI findings: ●● a linear/band-like area of reduced medullary SI extending to the cortex (Figs 6.60a, b) ●● surrounding marrow oedema with low SI on T1W and high SI on FS T2W FSE/STIR images

(Figs 6.60a, c, d)

●● a subchondral fracture: typically results from continued stress over the weight-bearing segment of a bone, classically the talar dome

●● clinically: it presents with acute onset of pain and is managed with non-weight-bearing in an attempt to prevent collapse of the articular surface and secondary OA

●● MRI findings: ●● in the acute stage: diffuse marrow oedema is demonstrated, with reduced T1W SI and increased FS

T2W/STIR SI (Figs 6.61a, b), the differential diagnosis being transient osteoporosis ●● at a later stage: there may be some resolution of the oedema and a thin subchondral hypointense fracture

line becomes evident (Figs 6.61c, d), which may be mistaken for ON

●● fractures of the APC: are uncommon when isolated, accounting for ~3% of calcaneal fractures, and if missed may proceed to non-union and persistent ankle pain

●● clinically: they usually occur in women (mean age 51 years) wearing high-heels and result from an inversion injury with a plantar-flexed foot, causing an avulsion injury of the bifurcate ligament and presenting as an ankle sprain

●● MRI findings: ●● diffuse marrow oedema within the APC (Figs 6.62a, b) ●● the fracture line is frequently vertically orientated (Figs 6.62c, d) and the fracture fragment is not

commonly displaced ●● associated injuries include:

● fractures of the talus and navicular ● ligament/tendon injuries, most commonly the ATFL (up to 50% of cases), the bifurcate ligament

(up to two-thirds of cases) and peroneus brevis ● injury to the bifurcate ligament: typically manifests as thickening with increased SI along either or

both of its bands, which normally extend from the APC to the navicular and cuboid

●● osteonecrosis (ON) of the talus: may be either traumatic or atraumatic ●● traumatic ON: typically occurs as a consequence of talar neck fracture or dislocation, vascular compromise

of the bone being at the level of the sinus tarsi and the risk of ON related to the fracture type (as classified by Hawkins): ●● type I: non-displaced talar neck fracture with ON risk of 0-15% ●● type II: displaced fractures with subluxation/dislocation of the subtalar joint and 20-50% risk of ON:

● the degree of displacement of type II fractures appears to predict the risk of ON, dislocation of the subtalar joint posing a greater risk compared to subluxation159

●● type III: displaced fractures with subluxation/dislocation of both the ankle joint and the subtalar joint, and almost 100% risk of ON

●● type IV: displaced fractures with subluxation/dislocation of the ankle joint, subtalar and talonavicular joints, and 100% risk of ON

●● resulting osteonecrosis involves the talar body and may progress to articular collapse and secondary OA ●● partial ON:160 has been described following type II or III fractures and is typically limited to the

anterolateral or superior portions of the talar body: ● patients with ON involving >50% of the talar body are believed to be more prone to articular collapse

●● atraumatic ON: is associated with steroid use, alcohol abuse, SLE, renal transplantation, sickle cell anaemia, hyperlipidaemia, radiotherapy, inherited thrombophilias and HIV infection161

●● ON of the calcaneus:162 is rare and typically involves the posterior half ●● MRI findings:

●● an area of poorly-defined SI abnormality within the talar body, surrounded by a hypointense line on T1W and hyperintense line on STIR images (Figs 6.63a, b)

●● the ‘double-line’ sign may be evident on T2W images, and marginal enhancement is seen following gadolinium, indicating a reactive zone of vascular granulation tissue

●● the size of the necrotic fragment can also be assessed (Figs 6.63c, d), with larger fragments being more likely to progress to articular surface collapse

●● transient osteoporosis: of the foot is a rare condition, which is manifest by the spontaneous onset of severe pain without a history of trauma, with plain radiographs showing osteopaenic bone and MRI showing features of marrow oedema: ●● it is more common in men and typically affects those aged 40-70 years ●● the condition typically affects more than 1 tarsal bone at presentation (mean 4.7 bones; range 2-14 bones)

and can affect any of the tarsal bones, with no particular predilection ●● symptoms usually resolve spontaneously in 3-12 months

●● transient bone marrow oedema syndrome (BMOS) of the foot:165 may represent a very similar entity, but presents in younger patients (10-27 years): ●● it is suggested that the term BMOS should be reserved for individuals, who despite their overlapping MRI

appearances, have no osteopenia on plain radiographs

●● MRI findings: ●● diffuse marrow oedema affecting multiple tarsal bones (Figs 6.64a-c), with associated soft-tissue

oedema (100%) (Figs 6.64a, b) and joint effusion (40%) ●● follow-up MRI at 1 year demonstrates:

● complete resolution of marrow oedema in 72%, partial resolution in 20% and no improvement in 8%

● the development of marrow oedema-like changes in the contralateral foot in 25% ● involvement of different bones in the same foot, or different regions of the same bones

●● CRPS: also known as post-traumatic osteoporosis, Sudek’s atrophy, reflex neurovascular dystrophy and reflex sympathetic dystrophy

●● it most often occurs following trauma (notably ankle dislocations and intra-articular fracture), burns, cancer and various central nervous system disorders, and most commonly results in diffuse involvement of the hand or foot

●● clinically: it presents with pain, hyperhidrosis and hypertrichosis with associated physical findings of oedema, warmth, redness, stiffness of the skin and limitation of joint movement: ●● it is more common in females, with a mean age at presentation of 56 years169 ●● 3 clinical stages are recognised with marked overlap, the hypertrophic/warm stage, the atrophic/vascular

instability stage and the stabilised/cold stage ●● MRI findings:

●● periarticular oedema and marrow oedema (Figs 6.65a, b) related to tendon and ligament insertions ●● occult stress fractures (reported at the talus and less commonly the tibia) (Fig. 6.65c) ●● tenosynovitis and soft-tissue oedema ●● fatty atrophy/infiltration of skeletal muscles may be seen in chronic cases ●● MRI may be normal, and therefore does not rule out CRPS

●● tarsal coalition: represents abnormal fusion between 2 or more tarsal bones and is a relatively common cause of ankle and foot pain

●● it is congenital in origin, being due to failure of formation with an autosomal dominant pattern of inheritance ●● the estimated prevalence is 1-2%, with the condition being bilateral in 50% of cases ●● coalitions are classified according to anatomical type and morphology:

●● ~90% involve the talocalcaneal (TC) or calcaneonavicular (CN) joints, with approximately equal incidence ●● TC coalition: is classified as intra-articular or extra-articular:

●● intra-articular TC coalition: typically involves the middle facet of the subtalar joint at the sustentaculum tali (Figs 6.66a, b), usually involving the entire joint

●● intra-articular coalition of the posterior subtalar joint is less common, typically only involving the posteromedial margin of the joint (Fig. 6.66c), while isolated anterior facet coalitions are rare (Fig. 6.66d)

●● extra-articular TC coalition: typically involves the interval between the posterior sustentaculum and the posteromedial process of the talus (Fig. 6.66e)

●● secondary signs: include talar beak (Fig. 6.66f), narrowing of the posterior subtalar joint, rounding of the lateral talar process and a ball-in-socket tibiotalar joint (in severe cases of juvenile TC coalition)

●● CN coalition: occurs between the anterior/dorsal process of the calcaneus and the posteromedial aspect of the navicular (Figs 6.66g, h): ●● it is associated with an elongated anterodorsal process of the calcaneus termed the ‘anteater’s nose’

(Fig. 6.66i), and hypoplasia of the talus ●● rarer coalitions: include calcaneocuboid, cuboid-navicular, navicular-medial cuneiform and multiple

coalitions in the same foot ●● morphologically: coalitions may be fibrous (syndesmosis), cartilaginous (synchondrosis) or bony

(synostosis) ●● clinically: patients usually present in the 2nd decade, symptoms becoming more pronounced with progressive

ossification of the coalition: ●● symptoms include hindfoot or tarsal pain/stiffness, or peroneal spastic flatfoot

●● MRI findings: ●● all coalitions should be demonstrated on a combination of coronal, axial and sagittal images ●● at least 1 FS T2W/STIR sequence should be employed to detect marrow and/or soft-tissue oedema ●● TC coalition: is optimally demonstrated on coronal MR images (Figs 6.66a, b) ●● CN coalition: is optimally demonstrated on sagittal and axial MR images (Figs 6.66g, h) ●● complete osseous coalitions: demonstrate continuous extension of marrow across the coalition

(Figs 6.67a, b) ●● incomplete fibrous coalitions: show intermediate/low T1W and T2W SI at the junction of the bones

(Figs 6.66g, h) ●● incomplete cartilaginous coalitions: show intermediate T1W SI and hyperintensity on T2W/STIR images

(Figs 6.67c, d) ●● subchondral cystic change (Fig. 6.67e) and stress-induced marrow oedema (Figs 6.67f, g) are also

prominent features, particularly in non-osseous coalitions presenting in adulthood ●● associated morphological features are as described above ●● pseudocoalition:26 typically occurs at the middle subtalar joint due to partial volume averaging of the

articular margin on coronal and sometimes axial images, and is occasionally seen on sagittal images between the calcaneus and navicular:

● it appears as an ‘osseous’ bar between the talus and calcaneus traversed by a poorly-defined hypointense horizontal line (Figs 6.67h, i), which migrates from cranial to caudal on sequential anterior images and is differentiated from true coalition by a normal appearance of the middle subtalar joint on sagittal images

●● the sinus tarsi: represents a cone-shaped cavity extending from a posteromedial to anterolateral direction ●● it is located in the lateral aspect of the midfoot between the neck of the talus and the anterosuperior

surface of the calcaneus (Figs 6.68a-c), serving as a boundary between the anterior and posterior subtalar joints

●● the sinus tarsi: continues medially as the tarsal canal, a funnel-shaped space that terminates immediately posterior to the sustentaculum tali

●● the sinus tarsi: contains fat, vessels, nerves and 5 ligamentous structures, which contribute to stabilisation and proprioception of the subtalar joint: ●● the medial, intermediate and lateral roots of the inferior extensor retinaculum ●● the cervical ligament: which runs between the cervical tubercle of the inferior and lateral aspects of the

talar neck and the dorsal aspect of the calcaneus, being seen on anterior coronal (Fig. 6.68d) and sagittal (Fig. 6.68e) images

●● the interosseous talocalcaneal ligament: which runs between the talus and calcaneus just anterior to the posterior subtalar joint, being seen on posterior coronal (Fig. 6.68f) and medial sagittal (Fig. 6.68g) images

●● sinus tarsi syndrome (STS): is a common complication of ankle sprains ●● aetiology: 70% are considered to be post-traumatic, related to injury to the internal ligaments and 30% are

due to miscellaneous causes including ganglion cysts, gout and PVNS ●● clinically: STS typically presents in the 3rd-4th decades, following a history of inversion injury, with persistent

lateral foot pain and a sensation of hindfoot instability: ●● pain is exacerbated by pressure over the lateral foot, walking or supination/adduction of the foot, and is

relieved by local anaesthetic injection into the sinus tarsi ●● associated injuries to the lateral ankle ligaments are common (up to 79% of cases)173

●● MRI findings: ●● replacement of normal sinus tarsi fat by:

● fluid/inflammatory tissue: with reduced SI on T1W/PDW (Fig. 6.69a) and increased SI on FS T2W/STIR images (Fig. 6.69b)

● fibrosis: with low SI on both T1W/PDW and T2W/STIR sequences (Figs 6.69c, d) ● enhancement of inflammatory tissue is a non-specific finding (Fig. 6.69e)

●● advanced disease is associated with OA in the posterior subtalar joint, cortical erosion (Fig. 6.69f), reactive marrow oedema (Figs 6.69g, h) and subchondral cysts (Figs 6.69c, d, h)

●● injury to the cervical or interosseous talocalcaneal ligaments (Figs 6.70a, b), which are not consistently demonstrated on conventional MRI due to their oblique course:

● MRI has a reported sensitivity and specificity of 44% and 60%, respectively, for interosseous talocalcaneal ligament tears, and 73% and 89% for cervical ligament tears174

●● ligament morphology may be better characterised on 3D volume sequences or using direct oblique planes175 ●● miscellaneous conditions: such as ganglion cyst (Figs 6.70c, d) and PVNS (Figs 6.70e, f ) ●● intraosseous ganglia of the calcaneus arising from the sinus tarsi are a common incidental finding

(Figs 6.70g, h)

●● the plantar fascia (PF): represents a multi-layered fibrous aponeurosis with central, medial (tibial) and lateral (peroneal) components, and functions to provide support to the longitudinal arch of the foot

●● the central component: is the largest and arises from the plantar aspect of the medial calcaneal tuberosity (Figs 6.71a, b), extending anteriorly, superficial to and adherent to the flexor digitorum brevis (FDB) muscle (Fig. 6.71c): ●● at the level of the mid-metatarsals, it divides into 5 branches; 1 inserting into the proximal phalanx of each

toe ●● the medial component: serves as a fascial covering for the underlying abductor hallucis (AbH) muscle

(Figs 6.71c, d) ●● the lateral component: arises from the lateral aspect of the medial calcaneal tuberosity (Fig. 6.71d) and

extends in the direction of the cuboid, dividing into medial and lateral bands which insert into the plantar plate of the 4th (occasionally 3rd) metatarsophalangeal joint(s) and the base of the 5th metatarsal, respectively (Fig. 6.71d): ●● it also forms the fascial covering for the abductor digiti minimi (AbDM) muscle (Fig. 6.71c), having a

variable appearance and occasionally being very thin or absent ●● the PF: is optimally assessed on a combination of sagittal and coronal MR images

●● on sagittal images: it has uniform thickness from the calcaneal tuberosity to its mid-point (Fig. 6.71a), after which it thins to its insertion into the phalanges

●● on coronal images: the inferior border is straight and all 3 components are visualised together (Figs 6.71b, c) ●● the normal fascia: is 2-4 mm in thickness and, typically, uniformly hypointense on all pulse

sequences (Figs 6.71a-c), but slight increased SI on T1W images may be observed in up to 21% of asymptomatic individuals,178 while increased SI on T2W/STIR sequences is uncommon in asymptomatic subjects (<8%)

●● plantar fasciitis: is the commonest cause of plantar heel pain, usually occurring due to repetitive trauma, which results in microtears and a local inflammatory reaction: ●● such cases are mostly associated with obesity in the middle aged or elderly, or are sports related injuries in a

younger age group, particularly associated with running or jumping ●● other causes: include systemic conditions such as DM, RA, gout and enthesopathy associated with

seronegative spondyloarthropathy, in which case it is usually bilateral and associated with Achilles tendinosis and retrocalcaneal bursitis

●● clinically: PF presents with pain on the undersurface of the heel on weight-bearing, with localised tenderness over the anteromedial portion of the plantar surface of the calcaneus: ●● pain is exacerbated by passive dorsiflexion of the toes

●● MRI findings: ●● focal, fusiform swelling (>4 mm) of the proximal aspect of the plantar fascia extending to the calcaneal

tuberosity (Figs 6.72a-c), with associated increased SI (Figs 6.72a-c)180 ●● oedema, best seen on FS T2W FSE/STIR images, in the adjacent fat pad and soft tissues (Fig. 6.72b),

is a common finding with both acute and chronic plantar fasciitis and occurring superficial and/or deep to the fascia

●● oedema in the calcaneal tuberosity (Fig. 6.72d), such changes being more pronounced when associated with enthesopathy and enhancing following gadolinium (Fig. 6.72e)

●● chronic/inactive plantar fasciitis manifests as fascial thickening with normal SI (Fig. 6.72f) ●● associated features:

●● calcaneal tuberosity oedema in the presence of associated Achilles tendinosis and retrocalcaneal bursitis should prompt a diagnosis of seronegative arthropathy177

●● a calcaneal heel spur (enthesophyte) may be present in ~50% of subjects:181,182 ● heel spur location: can be classified as superior to the PF (type A) (Fig. 6.72g) or within the PF

(type B) (Fig. 6.72h), the latter possibly associated with more severe symptoms183 ● however, calcaneal spur formation is a very non-specific appearance in isolation, being seen in ~20% of

asymptomatic individuals178

●● plantar fascia rupture: is typically a sports related injury associated with running or jumping, but may also occur following local corticosteroid injection: ●● individuals with preexisting plantar fasciitis (Figs 6.73a, b) are at 33-fold greater risk of rupture after

local corticosteroid injection,184 the reported incidence being 2.4%185 ●● clinically: it presents with sudden plantar heel pain and a palpable, tender mass:

●● rupture may be partial or complete and usually involves the proximal portion 2-3 cm from the calcaneal insertion (Figs 6.73c, d)177

●● MRI findings: ●● partial (Figs 6.73a, b) or complete interruption of the plantar fascia with markedly increased SI on FS

T2W/STIR images due to a combination of oedema and haemorrhage: ● partial tears typically involve the superficial fibres more than the deep fibres

●● thickening of the plantar fascia and perifascial fluid collections (Figs 6.73c, d) ●● tears may involve the underlying FDB muscle, which manifest as muscle oedema and haemorrhage ●● less commonly, tears involve the AbH or quadratus plantae muscles ●● chronic rupture: manifests as focal thickening and an intermediate or low SI scar, which shows no

enhancement following gadolinium

●● plantar fibromatosis: is also known as Ledderhose’s disease, being a relatively uncommon, benign but locally aggressive lesion

●● it is associated with palmar fibromatosis (Dupuytren’s contracture) in up to 65% of cases, and usually involves the central and medial portions of the plantar fascia

●● the resulting fibrous nodules are usually <3 cm in diameter ●● clinically: it is most commonly seen in the 30-50 year age range with a male predominance:

●● it is bilateral in 10-25%, presenting as a painless fibrous nodule or multiple nodules (in 33% of cases) in the plantar arch

●● single or multiple areas of nodular thickening of the superficial surface of the plantar fascia (Figs 6.74a-c) with low/intermediate SI on both T1W and T2W images (higher T2W SI if very cellular, seen in 22%) and variable contrast enhancement

●● linear tails of extension along the fascia (‘fascial tail’ sign) may be present and are often best seen following contrast

●● larger lesions may infiltrate the plantar musculature or the skin (Figs 6.74d-f)

●● the heel fat pad: acts as a shock absorber and is composed of elastic fibrous tissue septa separating closely packed fat cells (Figs 6.75a, b)

(Figs 6.75c-e)

●● the heel fat pad: may be a primary source of heel pain due to trauma and rupture of the fibrous septa, a situation particularly seen in obese, elderly patients

●● clinically: this results in fat pad atrophy causing heel pain, which is made worse by standing and may be confused with plantar fasciitis: ●● inflammation of the fat pad may occur as a sports injury in young adults

●● MRI findings: ●● fat pad atrophy: low SI fibrous bands/scarring and decreased height of the fat pad (Figs 6.76a, b) ●● fat pad inflammation: poorly-defined fat pad oedema (Figs 6.76c, d)

●● the tarsal tunnel: is a fibro-osseous canal located in the posteromedial aspect of the ankle/hindfoot, which may be divided into upper (tibiotalar) and lower (talocalcaneal) compartments: ●● the tibiotalar compartment: is covered by the deep aponeurosis of the calf, with the floor formed by the

posterior aspect of the tibia and talus (Figs 6.77a, b) ●● the talocalcaneal compartment: is covered by the flexor retinaculum and the AbH muscle with its fascia,

with the floor formed by the posteromedial aspect of the talus, the inferomedial aspect of the navicular and the medial aspect of the calcaneus and sustentaculum tali (Figs 6.77c, d), together with the quadratus plantae muscle (Figs 6.77c, e)

●● the tarsal tunnel: contains the tibialis posterior, FDL and FHL tendons and the posterior tibial neurovascular bundle (artery, vein and nerve)

●● the tibial nerve: trifurcates into its terminal branches ~1.5 cm proximal to the medial malleolus: ●● the terminal branches are: the medial (MPN) and lateral plantar (LPN) nerves, and the medial calcaneal

(MCN) nerve, which may also arise from the lateral plantar nerve in 16% of individuals ●● within the distal tarsal tunnel:

● the MPN: runs between the AdH and FDB muscles together with the median plantar artery and inferior to the FHL tendon (Figs 6.77f, g)

● the LPN: runs between the FDB and AbDM muscles together with the artery (Fig. 6.77g) ● the MCN: supplies sensory innervation to the medial heel and plantar fat pad

●● the inferior calcaneal nerve (ICN): is a mixed nerve arising from the LPN at the level of the medial malleolus, providing: ●● motor supply to the FDB, quadratus plantae and abductor quinti digiti muscles ●● sensory supply to the long plantar ligament and calcaneal periosteum

●● tarsal tunnel syndrome (TTS): is an entrapment neuropathy of the tibial nerve or its branches in the tarsal tunnel, and may be due to compression or tension neuropathy

●● nerve compression: occurs secondary to trauma (calcaneal fracture) or mass lesions, including synovial or ganglion cysts (Figs 6.78a, b), bone or soft-tissue tumours (Figs 6.78c, d), tenosynovitis (Fig. 6.78e), varicosities (Fig. 6.78f ), talocalcaneal coalition and an accessory or hypertrophied AdH muscle

●● tension neuropathy: occurs secondary to foot deformity, including varus deformity of the heel with forefoot pronation, and heel valgus with forefoot abduction

●● clinically: the presentation of TTS is variable depending upon the site of nerve compression: ●● patients complain of paraesthesia and a burning sensation in the plantar aspect of the heel and foot ●● examination findings include a positive Tinel sign (pain radiation on percussion of the nerve), and muscle

weakness, which is late and uncommon ●● neuropathy of the MCN: may be due to repeated microtrauma in joggers, fat pad atrophy associated with

sudden weight-loss, or diabetes ●● compression of the ICN (Baxter’s neuropathy):188 may be due to a hypertrophied AdH muscle

(e.g. in runners) or microtrauma (from a calcaneal spur or foot deformity) (Fig. 6.79a) and is often overlooked, likely accounting for up to 20% of cases of chronic heel pain: ●● it may occur in association with plantar fasciitis, resulting in denervation oedema (Figs 6.79b, c) or fatty

atrophy (Figs 6.79d, e) of the abductor digiti minimi (AbDM) muscle and possibly also quadratus plantae (Fig. 6.79f)190

●● entrapment of the MPN: between the AdH muscle and the Knot of Henry (cross-over point in the sole of the FDL and FHL tendons) may result in Jogger’s foot

●● MRI findings: ●● are related to the causes of nerve compression as listed above (Figs 6.78a-f) ●● rarely, there may be associated denervation oedema/atrophy of the plantar muscles (Figs 6.79a-f)

●● the sural nerve: at the ankle runs in the subcutaneous tissues lateral to the Achilles tendon, then inferior to the peroneal tendon sheath into the lateral aspect of the foot (Figs 6.80a-c), providing sensory supply to the lateral heel, ankle and foot

●● clinically: patients with sural neuropathy present with pain and paraesthesia of the lateral heel and foot ●● causes of sural nerve entrapment include:

surgical approach to the ankle joint or stripping of the lesser saphenous vein

●● the DPN: runs deep to the extensor retinaculum, lying lateral to the anterior tibial artery (Fig. 6.81a) and providing sensory supply to the 1st interspace and motor supply to the EDB muscle

●● DPN compression: may occur at 2 main sites, the anterior tarsal tunnel and the dorsum of the foot, being described in skiers wearing tight-fitting boots, and also in footballers and ballet dancers due to repetitive trauma

●● the anterior tarsal tunnel: is a flattened space between the IER and the fascia covering the talus and navicular, containing the DPN and tendons of EHL and EDL (Fig. 6.81b): ●● anterior tarsal syndrome: results from compression of the DPN by the EHL tendon as it runs through the

tunnel, resulting in dorsomedial foot pain and weakness of EDB (Fig. 6.81c) ●● the dorsum of the foot: where the sensory branch of the DPN runs between the extensor hallucis brevis

tendon and the deep fascia at the level of the 1st and 2nd tarsometatarsal joints: ●● compression: may be due to dorsal osteophytes from the talonavicular, naviculocuneiform or

cuneometatarsal joints, an os intermetatarseum, a high longitudinal arch or direct trauma

●● the mid-tarsal joint: is also termed Chopart’s or the transverse tarsal joint, and comprises the talocalcaneonavicular and the calcaneocuboid joints

●● the talocalcaneonavicular joint: is formed between the convex distal articular surface of the talus and the concave articular surface of the navicular (Figs 6.82a, b): ●● the articular surface of the navicular covers only a portion of the talar head ●● the talocalcaneonavicular joint can be considered as the ‘acetabulum pedis’, where the talar head

articulates with a socket (acetabulum) formed by the anterior and middle facets of the subtalar joint, the medial limb of the bifurcate ligament laterally, the spring ligament complex inferomedially and the navicular distally

●● dorsally, the joint is supported by a capsular thickening called the talonavicular ligament (Fig. 6.82a) ●● the calcaneocuboid joint: is formed by the distal articular surface of the calcaneus and the adjacent

proximal articular surface of the cuboid (Figs 6.82c, d), with ligamentous/capsular support being provided by: ●● the inferior (plantar) calcaneocuboid ligament (PCCL or short plantar ligament) inferiorly: which lies

between the bifurcate ligament and the long plantar ligament, arises from the antero-inferior calcaneus and inserts into the inferior aspect of the proximal cuboid, and is formed of a superficial (long) and stronger deep (short) layer (Figs 6.82c, e)

●● the medial calcaneocuboid ligament superomedially: which represents the lateral limb of the bifurcate ligament

●● the dorsolateral calcaneocuboid ligament: which originates from the anterior process of the calcaneus and extends over the dorsum of the cuboid (Fig. 6.82f)

●● the spring ligament complex: comprises a series of ligaments running from a superomedial to inferior direction between the anterior calcaneus and the navicular

●● it has 2 major functions: to support the talar head and provide support to the longitudinal arch of the foot

●● the spring ligament has 3 distinct components: ●● the superomedial calcaneonavicular ligament (CNL): which originates from the medial aspect of the

sustentaculum tali and inserts into the superomedial aspect of the navicular, being consistently visualised on coronal oblique (Fig. 6.83a) or axial (Fig. 6.83b) MR images:

● it has a mean thickness of 3.2 mm, blends with the tibiospring ligament (a division of the superficial deltoid ligament) at the consistently visualised transitional zone (Fig. 6.83c)195 and is commonly indistinguishable from the adjacent superficial TPT

●● the inferoplantar longitudinal CNL: which originates from the coronoid fossa of the calcaneus and inserts into the inferior beak of the navicular, being visible in 91% of MRI studies and optimally visualised on coronal images (Fig. 6.83d), but also seen in the sagittal plane (Fig. 6.83e):

● it has a mean thickness of 4 mm ●● the medioplantar oblique CNL: which originates in the coronoid fossa, just anterior to the middle

articular facet of the calcaneus and inserts into the medioplantar aspect of the navicular, being visualised in 77% of MRI studies, optimally in the axial oblique plane (Fig. 6.83f):

● it has a characteristic striated appearance and mean thickness of 2.8 mm

●● the spring ligament: blends laterally with the bifurcate ligament (of Chopart), a ‘Y-shaped’ ligament composed of medial and lateral parts: ●● medial: lateral CNL (Fig. 6.83f) ●● lateral: medial calcaneocuboid ligament (Fig. 6.83g) ●● it joins the anterior process of the calcaneus to the navicular and cuboid bones

●● the spring ligament recess:197 is a synovium-lined, fluid-filled space between the inferoplantar longitudinal CNL and the medioplantar oblique CNL, which communicates with the talocalcaneonavicular joint

●● acute tears: of the spring ligament have been reported but are rare ●● spring ligament abnormalities: are typically seen as a degenerative phenomenon in acquired flatfoot

deformity, being reported in 39-92% of patients with TPT dysfunction, with tears usually involving the superomedial CNL98,200

●● MRI findings: ●● ligament thickening, typically involving the proximal portion of the superomedial CNL (>5 mm), is

reported in 92% of surgically proven spring ligament injuries (Figs 6.84a, b):199 ● attenuation of the distal fibres of the superomedial CNL (<2 mm) is seen in up to 85% of cases

(Fig. 6.84c), and ligament discontinuity in ~80% ● a ‘wavy’ contour to the ligament may be present and increased ligament SI is seen in all cases

●● medioplantar ligament thickening (>7 mm) is seen in ~31% of cases while increased intrasubstance SI (away from its calcaneal attachment) is reported in ~38% of ligament injuries:199

● increased SI at its calcaneal sustentacular attachment is not considered pathological, usually representing interposed fat

●● associated TPT abnormality is present in 93% of cases (Fig. 6.84d) ●● however, surgically intact ligaments may also show thickening and increased T2W SI, although the

ligament appears continuous

●● the midfoot bones include: the navicular, cuboid and cuneiforms (medial, intermediate and lateral) ●● the navicular: is a disc shaped bone with posterior, anterior, dorsal and plantar surfaces:

●● the posterior surface articulates with the talar head at the talonavicular joint (Fig. 6.85a), although the posterior surface is larger than the talar head:

● the articular surface is typically biconcave, but may be flat, and is completely covered with articular cartilage

●● the anterior surface has a nephroid appearance, being concave inferiorly, while the anterior articular surface is convex, being divided into 3 articular surfaces by 2 slight crests (Fig. 6.85a):

● the medial surface: is the largest and articulates with the medial cuneiform bone ● the middle (intermediate) surface: articulates with the intermediate cuneiform ● the lateral surface: is the smallest and articulates with the lateral cuneiform

●● the dorsal surface: is convex and wider medially (Fig. 6.85b) ●● the plantar aspect: is irregular and continuous medially with the navicular tuberosity:

● a small prominence termed the ‘navicular beak’ may occasionally be present ●● the medial aspect: constitutes the navicular tuberosity, into which the TPT inserts (Figs 6.85a, b) ●● the lateral aspect has superior and inferior facets:

● the superior facet: provides insertion for the medial limb of the bifurcate ligament (lateral CNL) ● the inferior facet: articulates with the cuboid (Fig. 6.85b) and is continuous with the articular surface

of the lateral cuneiform

●● accessory navicular (os naviculare): 3 types are described with a collective prevalence of 4-21% of the population ●● type 1 (~11%): represents a separate ossicle/sesamoid bone lying within the distal tibialis posterior tendon (the

os tibiale externum): ●● it is round or oval, measuring 2-6 mm in dimension and is located up to 5 mm proximal to the navicular

tuberosity (Figs 6.86a, b) ●● type 2 (~4%): is triangular and measures 9-15 mm in size:

●● it has a fibrous or cartilaginous bridge to the adjacent navicular tuberosity (Figs 6.86c, d) and is bilateral in 50-90% of cases

●● type 3 (~5%): a cornuate navicular represents a secondary ossification centre, which is completely fused to the navicular tuberosity (Figs 6.86e, f )

●● stress fracture:204 is typically a sagittally orientated fracture involving the central third, due to the relatively decreased vascularity and high mechanical load present at this site: ●● clinically: it typically presents with vague midfoot pain aggravated by running or jumping, most

commonly described in athletes including basketball players and footballers ●● they are considered at high risk for delayed union, non-union or complete fracture ●● MRI findings: a sagittal hypointense fracture line with adjacent marrow oedema (Figs 6.87a, b), with

non-union manifesting as a persistent fluid SI gap at the fracture site ●● ON:145 when occurring in children is termed Kohler’s disease, while spontaneous ON of the navicular in

adults is termed Mueller-Weiss syndrome: ●● Mueller-Weiss syndrome: is four times more common in females and is often bilateral:

● typically, it follows a more painful course than Kohler’s disease and may progress to permanent, often disabling deformity

●● secondary ON: is most commonly post-traumatic, but also occurs due to any systemic cause predisposing to ON, typically being unilateral

●● deformity and collapse initially involve the lateral aspect of the bone, which consequently becomes comma-shaped, leading on to superior protrusion of the fragments

●● MRI findings: oedema/sclerosis in the navicular (Figs 6.87c, d), with collapse and fragmentation in the later stages (Figs 6.87e, f )

●● symptomatic accessory navicular109,205: type 2, and less commonly type 3 accessory navicular bones may become symptomatic, resulting in focal medial midfoot pain: ●● MRI findings: oedema within a type 2 accessory navicular is seen in all cases (Figs 6.88a, b):

● occasionally, oedema is present within the adjacent navicular (Fig. 6.88c) and high SI is seen in the synchondrosis (Fig. 6.88d), which may be widened (Fig. 6.88e)

● adjacent soft-tissue oedema occurs in 67% (Fig. 6.88d) and TPT pathology (see above) in 75% of cases

● a symptomatic type 3 navicular: may show overlying soft-tissue oedema or adventitial bursa formation

●● subarticular geode: of the proximal navicular articular surface is a not uncommon finding and may be a cause of midfoot pain, the lesion often associated with prominent marrow oedema (Figs 6.89a-c)

●● navicular OCD: is a rare lesion with a combined chondral and subchondral defect and associated reactive marrow changes (Figs 6.89d-f)

Cuboid and Cuneiforms ●● cuboid/cuneiform oedema may be seen in the setting of BMOS (Fig. 6.64) ●● oedema in the inferolateral aspect of the cuboid is a feature of peroneus longus tendinopathy and tears

(Figs 6.42e, f )119

●● the tarsometatarsal (TMT) joint: comprises the articulation between the cuneiforms and cuboid with the bases of the metatarsals (MT) (Figs 6.90a, b): ●● the base of the 1st MT articulates with the medial cuneiform ●● the base of the 2nd MT articulates with the intermediate cuneiform, and is recessed proximally compared

to the remaining metatarsal bases, adding stability to the joint (Fig. 6.90a) ●● the base of the 3rd MT articulates with the lateral cuneiform ●● the bases of the 4th and 5th MTs articulate with the cuboid

●● minor malalignment between the components of the 1st-3rd TMT joints is frequently seen;205 these may be either medial or lateral, most commonly at the 1st and 2nd TMT joints

●● pseudosubluxation:26 of the Lisfranc joint occurs at the 2nd TMT joint on coronal MR images, due to incongruent articular surfaces caused by variation in shape of the base of the 2nd metatarsal bone

●● the Lisfranc ligament complex (first interosseous ligament):206 is the largest of the ligaments supporting the Lisfranc joint: ●● it arises from the lateral aspect of the medial cuneiform (MC), inserts into the medial base of the 2nd

metatarsal (MT2) and is composed of three distinct, obliquely orientated bands (Figs 6.90c-e): ● the interosseous MC-MT2 ligament (Lisfranc ligament proper) (Figs 6.90c, e) ● the dorsal Lisfranc ligament, which connects the dorsum of C1 and M2 (Fig. 6.90e) ● the plantar Lisfranc ligament, which is stronger and most commonly has a single origin from the

plantar aspect of the MC with separate bundles to the plantar surface of MT2 and MT3 (Figs 6.90d, e)

●● the plantar band is intimately associated with the adjacent MC-IC interosseous ligament, plantar ligaments and peroneus longus tendon

●● the ligament is optimally demonstrated in the axial plane ●● the TMT ligaments: bridge the dorsal and plantar aspect of each TMT joint ●● the intermetatarsal ligaments: connect the bases of the 2nd-5th metatarsals (Fig. 6.91a) and have dorsal,

interosseous and plantar components ●● additional midfoot ligaments: include the dorsal intercuneiform ligaments (DICL) (Fig. 6.91b) and the

cuneometatarsal ligament (CML) (Fig. 6.91c) ●● the long plantar ligament (LPL) (Figs 6.91d-f): arises from the plantar surface of the calcaneus and cuboid

bones, inserts into the 2nd-5th metatarsal bones and aids in maintaining the longitudinal arch of the foot

●● injury to the Lisfranc joint: can be caused by high or low velocity trauma resulting in different patterns of injury

●● high impact injury: refers to a Lisfranc fracture-subluxation or fracture-dislocation and is rare, being reported in 1:55,000 individuals: ●● it most commonly follows severe trauma from an road traffic accident (RTA), crush injury or a fall from a

height with resulting abduction and/or plantar flexion applied directly to the joint ●● fracture types include:

● homolateral: where all 5 metatarsal bases are displaced in the same direction in the coronal plane ● divergent: when there is separation of the 1st and 2nd metatarsal bases

●● low impact Lisfranc injury: is also referred to as a midfoot sprain, being fairly common in athletes and reported in up to 4% of American football players per season:212 ●● it typically follows indirect trauma to the Lisfranc joint, including a twisting injury, forced plantar flexion

or forefoot abduction and results in ligamentous failure, although a small avulsion fracture of the base of the 2nd metatarsal may occur

●● MRI may reveal unstable Lisfranc ligament injuries in suspected midfoot sprains despite normal weightbearing radiographs213

●● periligamentous soft-tissue oedema, manifest as increased SI on FS T2W/STIR images (Figs 6.92a, b) or elongation of the interosseous ligament in lower grade injury

●● partial tears of the Lisfranc ligament complex more commonly affect the dorsal or interosseous ligament than the stronger plantar component207,214

●● complete discontinuity of the interosseous fibres or plantar Lisfranc ligament may occur in higher grade injuries (Figs 6.92a, b)

●● tears of the intermetatarsal ligaments, which typically involve the weaker dorsal fibres before the stronger plantar fibres

●● loss of alignment between the medial cortex of the second MT base and the intermediate cuneiform (Fig. 6.92c), fractures of the MT bases and tarsal bones (Fig. 6.92d)

●● on sagittal images, slight dorsal subluxation of the 2nd TMT joint may be evident (Fig. 6.92d)

●● neuropathic arthropathy: occurs in ~0.1-0.4% of patients with DM, which is the commonest cause of neuropathic foot and typically affects the TMT, intertarsal and metatarsophalangeal joints

●● clinically: it typically occurs in the 5th-6th decades in patients with dense, symmetrical neuropathy and who have been diabetic for >10 years:

●● in diabetic patients with established peripheral neuropathy, the incidence of neuropathic arthropathy is 29-35%219

●● in the acute stage, it commonly presents with pain, erythema and swelling, while chronic disease results in foot deformity that may be complicated by skin ulceration, which itself predisposes to cellulites and osteomyelitis

●● typical foot deformities include: ● superior displacement of the metatarsal bases ● the tarsal bones, particularly the cuboid may become weight-bearing, with collapse of the longitudinal

arch and ‘rocker-bottom’ feet ● lateral splaying of the MT bases and lateral splaying at Chopart’s joint

●● bone and joint involvement may be classified into 5 types: ● type 1: metatarsophalangeal and interphalangeal joints ● type 2: tarsometatarsal joints ● type 3: the tarsal joints ● type 4: the subtalar joints ● type 5: the calcaneus

●● forefoot disease carries a good prognosis, whereas hindfoot deformity is rare and carries a poor prognosis

●● MRI findings: ●● acute disease: diffuse soft-tissue oedema (Figs 6.93a, b), rupture of the Lisfranc ligament, with little

deformity or malalignment: ● joint effusion and subchondral oedema with reduced T1W SI and hyperintensity on FS T2W/

STIR (Figs 6.93a, b), marginal erosions and subchondral and periarticular soft-tissue enhancement following gadolinium (Fig. 6.93c)

●● in subacute disease: joint destruction with subchondral cyst formation (Fig. 6.93d), erosions and bone fragmentation (Figs 6.93e) and fractures, which may be subchondral in location (Fig. 6.93f)

●● chronic neuroarthropathy: manifests as cortical fragmentation with joint subluxation/dislocation/ disorganisation (Figs 6.94a, b):

● altered marrow SI, with hypointensity on both T1W and T2W images, corresponding to marrow sclerosis

● periarticular cysts, periostitis in the metatarsals and phalanges ● soft-tissue callus and ulcer formation at pressure points (Figs 6.94c, d)

●● neuropathic arthropathy: and osteomyelitis in diabetics may appear radiologically similar features that are more suggestive of infection include:

● 1: osteomyelitis most commonly occurs due to direct spread from adjacent skin ulceration and cellulitis and therefore, marrow SI changes without adjacent skin changes are unlikely to be infective in aetiology

● 2: the distribution of osteomyelitis mirrors that of ulceration/cellulitis and therefore, infection is most common at the toes, MT heads, calcaneus and malleoli

● 3: osteomyelitis tends to remain localised or spreads contiguously, whereas neuropathic arthropathy tends to involve several joints in the same region

●● neuropathic arthropathy with superadded infection is suggested by:220 ● the presence of joint effusion with diffuse joint fluid/synovial enhancement, as opposed to thin rim

enhancement ● fluid collections in the soft tissues are more common (10-50% of cases) and are larger than those seen

with non-infected joints (Figs 6.94e, f ) ● soft-tissue fat replacement and sinus tracts (Figs 6.94c, d) ● diffuse or extensive (rather than subchondral) marrow oedema, especially with enhancement

(Figs 6.94e, f ) ● the absence of subchondral cysts ● the ‘ghost sign’:221 areas of osteomyelitis are more conspicuous on contrast-enhanced T1W images

●● MRI has a sensitivity and specificity of 90% and 79%, respectively, for detecting osteomyelitis underlying diabetic foot ulcers222

●● osteomyelitis in the foot: is a common complication of DM and bone infection may spread to the soft tissues and involve the adjacent tendons

●● tendon involvement: is reported to occur in 43% of cases of forefoot pedal osteomyelitis and 44% of cases of hindfoot osteomyelitis

●● it is invariably associated with adjacent skin ulceration and with a soft-tissue abscess in 21% of cases ●● forefoot involvement: more commonly affects the flexor tendons, most commonly of the 1st and 2nd rays, with

proximal spread possibly resulting in central plantar abscess formation ●● hindfoot involvement: most frequently results in peroneal tenosynovitis (adjacent to lateral malleolus

ulceration), or distal Achilles tendon infection (adjacent to calcaneal ulceration) ●● MRI findings:

●● increased tendon SI, tendon swelling and enhancement following contrast ●● peritendinous fluid and adjacent soft-tissue abscess (Fig. 6.94f) ●● these findings can be seen with both tendon infection and peritendinous infection

●● the midfoot muscles: can be divided into the plantar and dorsal compartments ●● the plantar compartment includes:

●● the abductor hallucis (AbH) muscle: arises from the medial process of the calcaneal tuberosity and flexor retinaculum (Fig. 6.95a) and runs in the medial aspect of the foot (Fig. 6.95b) to insert into the medial side of the base of the proximal phalanx of the great toe

●● the flexor hallucis brevis (FHB) muscle: has 2 muscle bellies, between which the tendon of FHL passes to its insertion (Fig. 6.95c):

● FHB arises from the plantar aspect of the cuboid (Fig. 6.95d), the adjacent lateral cuneiform, the TPT and the medial aspect of the 1st metatarsal bone

● the tendon of the medial belly joins the AbH muscle and inserts into the medial base of the proximal phalanx of the great toe

● the tendon of the lateral belly joins the adductor hallucis (AdH) and inserts into the lateral base of the proximal phalanx of the great toe

● the medial and lateral sesamoids are embedded in the medial and lateral tendons of FHB ●● the flexor digitorum brevis (FDB) muscle: arises from the medial tuberosity of the calcaneus and

posterior third of the plantar aponeurosis (Fig. 6.95e) and is the most superficial plantar foot muscle (Fig. 6.95b):

● its insertion consists of 4 tendons that insert into the lateral 4 toes ●● the quadratus plantae (QP) muscle: is also known as flexor digitorum accessorius and has 2 heads, a large

medial muscular head that arises from the medial calcaneus (Figs 6.95a, e) and a flat tendinous head that arises from the lateral margin of the inferior calcaneus and long plantar ligament:

● it joins the FDL tendons (Fig. 6.95b) to insert into the MTs and acts to assist flexion of the 2nd-5th toes

●● the AbDM muscle: arises from the calcaneal tuberosity (Fig. 6.95a), runs in the lateral aspect of the foot (Fig. 6.95b) and inserts into the base of the little toe proximal phalanx, abducting and flexing the little toe

●● the dorsal compartment comprises: ●● the EDB and EHB muscles and tendons: which arise from the superior and lateral aspect of the calcaneus

(Fig. 6.95f) and extensor retinaculum and lie deep to the EDL tendon (Fig. 6.95b): ● the EDB muscle divides into 4 tendons that insert into the medial 4 toes ● the most medial is the EHB tendon, which inserts into the base of the proximal phalanx of the

great toe, and is frequently described as a separate muscle

Introduction ●● the forefoot consists of:

●● bones: the metatarsals and phalanges ●● joints: the metatarsophalangeal and interphalangeal joints ●● associated: muscles, tendons and nerves

The Bones Normal Anatomy ●● the MT bones: are long tubular bones composed of a base, body and head (Figs 6.96a, b), which provide an

important site of attachment for both ligaments and muscles: ●● the bases: articulate with the tarsal bones at the Lisfranc joint ●● the bodies: are triangular in cross-section, becoming tapered distally (Fig. 6.96c) ●● the heads: expand distal to the neck and form the proximal articular surfaces of the metatarsophalangeal

(MTP) joints ●● the flattened sides of the heads have small tubercles for the attachments of the collateral ligament complex

(CLC) (Fig. 6.96d) ●● the 1st MT is the shortest and widest, having 2 flat surfaces on the plantar aspect of its head for articulation

with the tibial and fibular sesamoid bones ●● the 2nd MT is usually the longest

●● the os intermetatarseum (OI):109,224 is an accessory ossicle located on the dorsum of the foot between the bases of the 1st and 2nd metatarsals (Figs 6.96e, f ): ●● it has a reported incidence in cadaver studies of 8-12.5% and in radiographic studies of 0.2-6.8%, being

bilateral in 33% of cases ●● symptomatic OI: produces pain over the dorsum of the midfoot at the metatarsal base level due to

compression of branches of either the deep or superficial peroneal nerves ●● the phalanges (proximal, middle and distal): provide attachment points for the extensor and flexor tendons

(Figs 6.96g, h)

●● stress injuries: may be classified as either fatigue or insufficiency ●● fatigue fractures: are most commonly seen in runners (accounting for 20% of their lower limb stress fractures),

ballet dancers, gymnasts and military recruits: ●● stress fractures typically occur in athletes who have rapidly increased their training, or subjects

undertaking unaccustomed exercise, e.g. military recruits, within their first 3 months94,228 ●● insufficiency fractures: are most commonly seen in osteoporosis, as well as conditions that result in altered

weight-bearing, including: ●● hallux valgus deformity, recent surgery to the hallux, a low longitudinal arch to the foot, tarsal coalition

and tendon abnormalities ●● they most commonly involve the middle or distal portions of the 2nd, 3rd or 4th metatarsals, while ballet

dancers have a propensity to stress fractures of the MT bases (Fig. 6.97a):229 ●● subchondral fractures of the metatarsal heads may occur in diabetic neuropathic arthropathy and stress

reactions may be associated with long-term pain if not appropriately treated with avoidance of weightbearing

●● MRI findings: ●● stress fracture: appears as a hypointense band running perpendicular to and in contact with at least

1 metatarsal cortex (Fig. 6.97a): ● marrow SI abnormality with hypointensity on T1W (Fig. 6.97b) and hyperintensity on FS

T2W/STIR images due to oedema (Figs 6.97c, d) ● periosteal/soft-tissue oedema (Figs 6.97b-d)

●● stress reaction/response: is diagnosed in the presence of marrow oedema with no evidence of an associated fracture line (Fig. 6.97e), although soft-issue oedema and contrast enhancement may also be seen

●● fracture healing: manifests as the development of circumferential callus with reduction of marrow and soft-tissue oedema (Figs 6.97f, g), with healed lesions showing mature callus and normal marrow SI (Figs 6.97h, i)

●● Freiberg’s infraction: represents a disorder affecting the metatarsal head, usually the 2nd (68% of cases) or 3rd (28%) ●● pathologically: it is characterised by collapse of the subchondral bone, ON, cartilaginous fissures and, eventually,

secondary OA, and is thought to result from acute or repetitive trauma, being bilateral in 10% of cases ●● clinically: it is most commonly seen in adolescent females presenting with pain and reduced joint motion, but

may be asymptomatic until the development of secondary OA: ●● primary ON of the metatarsal heads in older individuals is uncommon

●● early: marrow oedema in the MT head with reduced SI on T1W images (Fig. 6.98a) and increased SI on FS T2W/STIR images (Fig. 6.98b):

● these are non-specific changes, which may also represent a stress response in the metatarsal head ● a subchondral fracture line with flattening of the MT head (Figs 6.98c, d)

●● late: fragmentation of the MT head with intra-articular loose bodies (Figs 6.98e, f ), reduced SI on T2W images, widening of the joint space and, eventually, OA

●● the medial (tibial) and lateral (fibular) hallux sesamoids: are embedded within the medial and lateral tendon slips respectively of the FHB muscle at the level of the 1st metatarsal head (Figs 6.99a-c)

●● additional tendinous attachments include: the abductor hallucis (AbH) tendon on the medial side and the adductor hallucis (AdH) tendon on the lateral side

●● the sesamoids: are separated by a small ridge, the crista (Fig. 6.99c), on the plantar surface of the MT head and articulate with the head via hyaline cartilage, forming a synovial joint

●● the sesamoids: are embedded in the plantar plate, connected by the thick intersesamoid ligament (Fig. 6.99d) and further stabilised by the medial and lateral capsular ligaments and phalangeal-sesamoid ligaments

●● the distal FHL tendon: runs between the sesamoids (Figs 6.99d, e) and is stabilised by the fibrous plantar plate ●● the tibial sesamoid: is typically elliptical while the fibular sesamoid is cylindrical in shape, and is more

commonly bipartite, with reported incidence of 4-33.5% (Figs 6.99f-h), and a combined bipartite sesamoid is typically larger than a non-partite sesamoid

●● the function of the sesamoids: includes protecting the FHB tendons, acting as a fulcrum to increase the mechanical advantage of these tendons, and serving as a primary weight-bearing portion of the foot

of the foot ●● stress injuries: may involve the sesamoids (Figs 6.100a, b) or the synchondrosis between a bipartite sesamoid

(Figs 6.100c, d), and is usually an overuse injury affecting people who perform exercises that produce forced propulsion off a dorsiflexed toe, such as ballet dancers and sprinters

●● acute fractures: are also seen but are less common and are typically transverse in orientation (Fig. 6.100e): ●● delayed union and non-union frequently complicate sesamoid fractures, but are more prevalent in stress

fractures ●● ON: is difficult to differentiate clinically and radiologically from a stress fracture/sesamoiditis ●● all of these conditions are more common in young women and usually affect the tibial sesamoid ●● hyperextension injury: may result in rupture of the plantar plate or intersesamoid ligament, the latter being

associated with sesamoid subluxation/dislocation ●● the hallux-sesamoid complex: may also be affected by arthritic conditions such as OA, RA and seronegative

arthropathy ●● MRI findings:

●● sesamoiditis: manifests as normal or reduced T1W marrow SI (Fig. 6.100a) with increased FS T2W/ STIR SI (Fig. 6.100b):

● these SI changes are similar to those seen with stress injuries ● however, sesamoiditis is the more likely diagnosis if the SI is normal on T1W images, if both sesamoids

are involved and if associated reactive soft-tissue abnormalities (tendinosis, synovitis, bursitis) are present (Fig. 6.100f)

●● acute fractures: typically result in irregular, non-sclerotic margins with some degree of separation of the fragments, while a bipartite sesamoid typically demonstrates rounded fragments with smooth sclerotic margins:

● symptomatic non-union within a sesamoid fracture fragment manifests as persistence of marrow oedema234

●● the presence of extensive fragmentation is indicative of ON and usually excludes acute or stress fractures ●● in advanced cases, cortical irregularity, cyst formation, sclerosis and fragmentation may occur ●● hallux-sesamoid OA: manifests as articular cartilage loss, subchondral oedema/cysts and marginal

osteophytes (Figs 6.100g, h)

●● the metatarsophalangeal joints (MTPJs): are synovial ball-and-socket joints between the metatarsal heads and the bases of the proximal phalanges

●● the lesser MTPJs (2nd-5th): are stabilised by a fibrous capsule, the fibrocartilaginous plantar plate and the intracapsular CLC: ●● the fibrous capsule: appears as a thin hypointense structure around the joint margin (Fig. 6.101a) ●● laterally, the capsule is thickened by the CLC (Figs 6.101a, b), while on the plantar surface of the joint,

it is replaced by the plantar plate ●● the CLC: is formed of 2 components (which are not easily separable on MRI), the main collateral ligament and

the accessory ligament, both of which originate proximally from the dorsal tubercles of the metatarsal head: ● the main collateral ligament attaches distally to the base of the proximal phalanx (Fig. 6.101b), while

the accessory ligament takes a more vertical orientation, attaching distally to the plantar plate

●● the tendons: of the interosseous muscles also insert at the base of the proximal phalanx (Fig. 6.101c) ●● the plantar plate: is demonstrated on sagittal (Fig. 6.101d) and coronal (Fig. 6.101e) images as a

hypointense biconcave structure attached laterally to the CLC, proximally to the metatarsal head and distally to the base of the proximal phalanx:

● on sagittal images it measures ~20 mm in length and 2 mm in depth, while on coronal images it measures ~9 mm in width

● a normal high SI zone at the mid-line insertion of the plantar plate represents hyaline cartilage undercutting the plantar plate: – this is visible in all 3 planes as a discreetly marginated bright PDW/T2 SI zone measuring up to

2.5 mm in length (Fig. 6.101d) ●● the deep transverse metatarsal ligament (DTML): is identified on coronal images as a thick hypointense

structure running between the lateral margins of the adjacent plantar plates (Fig. 6.101e) ●● plantar to the joint: are the FDL and FDB tendons, which are contained within a common tendon sheath

stabilised by a fibrous pulley attached to the plantar plate (Figs 6.101d, e), with the FDB tendon lying plantar to the FDL

●● dorsal to the capsule: is the extensor hood, which arises from the sides of the EDL tendon sheath (Fig. 6.101f) and inserts into the plantar plate, DTML and base of the proximal phalanx

●● the abductor digiti minimi (AbDM) and flexor digiti minimi brevis (FDMB) tendons also insert into the lateral aspect of the 5th metatarsal base

●● the intermetatarsal spaces:240 are separated into 2 levels (superior and inferior) by the DTML: ●● the superior level: lies above the DTML and between the MTPJs and contains the interosseous tendons,

the AdH tendon (in the 1st interspace) and the intermetatarsal bursae (Fig. 6.101g): ● normally, intermetatarsal bursae are not identifiable on conventional MRI but may measure up to

3 mm in transverse diameter as a physiological finding226 ●● the inferior level: lies under the DTML, above the superficial transverse metatarsal ligament (STML)

(Fig. 6.101h) and between the perforating fibres (thin fibrous septa that run vertically between the margins of the plantar plate and the STML, containing the flexor tendon sheath):

● it contains the lumbrical muscle and the neurovascular bundle (Fig. 6.101h)

●● hallux valgus (HV) and hallux rigidus (HR): are the commonest degenerative disorders of the 1st MTPJ ●● HV: represents lateral deviation of the big toe at the MTPJ and is often associated with primary metatarsus

varus: ●● lateral deviation of the toe is measured by the metatarso-phalangeal angle, which is normally <15°

(Fig. 6.102a) ●● medial deviation of the 1st metatarsal is measured by the intermetatarsal angle, which is normally <9°

(Fig. 6.102b) ●● HR: represents a painful, motion limiting OA ●● MRI findings:

●● HV: medial bony eminence from the 1st MT head (95%) (Fig. 6.102a): ● sesamoid proliferation and displacement (90%) (Figs 6.102c, d) and bursa formation around the 1st

MT head (70%) (Figs 6.102e, f ) ● less common findings include rounding of the MT head and a lateral osteophyte from the base of the

MT head (Fig. 6.102g) ● shift of tendon position at the 1st MT head:242 a more plantar insertion of the AbH muscle tendon and

bowstringing of the flexor and extensor tendons across the 1st MTPJ ●● HR: dorsal (77%) and lateral osteophytes (69%) from the 1st MT head:

● subarticular geodes (54%) and marrow oedema (31%) (Figs 6.103a-c)

●● instability of the MTPJs: may occur as a consequence of chronic synovitis and stretching of the joint capsule and CLC

●● plantar plate disruption: involving the 2nd-5th MTPJs most commonly occurs in women resulting from increased weight-bearing load and hyperextension associated with wearing high-heeled shoes, and typically affects the 2nd MTPJ

●● turf toe: most commonly occurs in football players using lightweight flexible shoes on hard surfaces or artificial pitches, and represents a hyperextension injury of the 1st MTPJ resulting in sprain, partial rupture or complete rupture of the fibrocartilaginous plantar plate: ●● more severe hyperdorsiflexion injury may result in an associated sesamoid fracture or MTPJ

dislocation227,245 ●● up to 45% of professional American football players are reported to experience a turf toe injury at least

once during their careers246,247

●● MRI findings: ●● plantar plate disruption: increased FS T2W/STIR SI in and around the plantar plate (Figs 6.104a, b),

more common distally and on the lateral side: ● discontinuity of the plantar plate (Figs 6.104a, b), MTPJ and flexor tendon sheath synovitis with

persistent hyperextension of the proximal phalanx ● focal full-thickness defects of the plantar plate may result in formation of a submetatarsal synovial

cyst/ganglion (Figs 6.104c, d) ● sprains/partial thickness tears of the plantar plate manifest as an indistinct plantar plate with attenuation

(Fig. 6.104e) or thickening237 ● MRI has a reported sensitivity, specificity and accuracy of ~74%, 100% and ~88%, respectively, for

plantar plate injury when compared with surgical findings248,249 ● MR arthrography: may also be useful in the diagnosis of plantar plate disruption and capsular tears,

reportedly improving visualisation of the capsule, plantar plate and CLC:250,251 – contrast medium extension to the flexor tendon sheath is considered diagnostic of a plantar

plate tear252,253 ●● turf toe: partial or complete discontinuity of the plantar plate (Fig. 6.104f), with increased FS

T2W/STIR SI in the soft tissue on the plantar side of the sesamoid bones and associated injury to the articular cartilage and subchondral bone (Figs 6.104f, g):

● proximal retraction of the sesamoids may be seen with complete plantar plate disruption ● chondral injuries may be seen, the presence and extent of which can affect surgical management

●● bursitis: may involve either the intermetatarsal bursae or adventitial bursae beneath the metatarsal heads ●● causes include: trauma, RA (Figs 6.105a, b) and gout ●● intermetatarsal bursitis: is a relatively common differential diagnosis for Morton’s neuroma and may cause

pain by direct compression of the digital nerve or contribute to perineural fibrosis ●● MRI findings:

●● adventitial bursa: a well-defined fluid collection with low-intermediate T1W/PDW SI and high FS T2W/ STIR SI deep to the MT head (Figs 6.105c, d), showing rim enhancement following gadolinium, or a more solid appearance when chronic with low T2W SI (Figs 6.105e, f )

●● intermetatarsal bursa: a well-defined fluid-filled structure between the metatarsal heads above the DTML, with high SI on T2W/STIR images and low SI on T1W images (Figs 6.105g, h):

● however, this may represent a non-specific finding for bursitis since fluid in at least 1 intermetatarsal space is visible in ~70% of asymptomatic individuals, being limited to the first 3 interspaces and rarely exceeding 3 mm in transverse diameter (Fig. 6.101g)

● subtle peripheral enhancement following contrast administration is usually seen

●● the forefoot muscles: include the AdH muscle, the FDMB muscle and the deep intrinsic muscles ●● the AdH muscle: serves to adduct the great toe, flex the MTPJ and maintain the transverse arch of the foot:

●● it has an oblique head arising from the 2nd-4th metatarsal bases (Fig. 6.106a) and a transverse head originating from the plantar ligaments of the 2nd-5th MTP joints (Fig. 6.106b), which insert together into the lateral base of the proximal phalanx of the great toe (Fig. 6.106c), together with the lateral tendon of FHB

●● the FDMB muscle: flexes the little toe at the MTP joint: ●● it arises from the base of the 5th metatarsal and peroneus longus tendon sheath and runs

adjacent to the AbDM tendon (Fig. 6.106d) to insert into the lateral base of the proximal phalanx of the little toe

●● the deep intrinsic muscles: consist of the lumbricals (total 4) and interossei (3 plantar and 4 dorsal): ●● the lumbricals (Fig. 6.106e): originate from the FDL tendons and insert into the bases of the lateral 4

proximal phalanges ●● the plantar interossei (Fig. 6.106f): are adductors and originate from the medial 3rd-5th metatarsals and

insert into the medial bases of the 3rd-5th proximal phalanges ●● the dorsal interossei (Fig. 6.106f): are abductors and originate from the adjacent sides of the 2 metatarsals

between which they lie: ● the 1st inserts medially on the 2nd toe proximal phalanx and the 2nd-4th insert laterally on the 2nd-4th

toe proximal phalanges

●● the medial plantar nerve: has 4 digital branches, the most medial of these being a proper digital nerve running to the medial aspect of the great toe: ●● the remaining 3 are called 1st, 2nd and 3rd common digital nerves ●● each of these divides into 2 branches (digital nerves) at the levels of the 1st, 2nd and 3rd intermetatarsal spaces

●● the lateral plantar nerve: divides into a superficial branch that runs to the lateral side of the little toe forming a proper digital nerve, and a common digital nerve running to the 4th intermetatarsal space

●● the nerves: are optimally visualised on images obtained perpendicular to the metatarsal heads (Fig. 6.101h)

●● Morton’s neuroma: represents a perineural fibrosis and nerve degeneration of the common digital nerve, usually occurring in the 3rd and/or 2nd plantar intermetatarsal spaces

●● it does not represent a true neuroma, but rather a fibrous lesion resulting from repetitive irritation: ●● intermetatarsal bursitis may be a contributing factor to subsequent perineural fibrosis due to its close

proximity to the digital neurovascular bundle

●● clinically: it is more common in women, with highest prevalence in 5th and 6th decades of life, most commonly presenting with localised forefoot pain which may be sharp or dull, and can radiate to the toes or into the leg: ●● the symptoms are typically worsened by wearing shoes or by walking, and relieved when the foot is not

weight-bearing ●● however, Morton’s neuromas may be identified in 30-33% of asymptomatic individuals, although

asymptomatic neuromas are significantly smaller in diameter than symptomatic neuromas, there being a large overlap between the 2 groups

●● it is suggested that neuromas greater than 5 mm in transverse diameter are likely to be symptomatic, as well as those associated with intermetatarsal bursitis259

●● in the presence of a smaller neuroma, an alternative cause for forefoot pain should be sought ●● MRI findings:

●● a well-defined, spindle shaped mass between the MT heads (Figs 6.107a-c) on the plantar side of the DTML

●● isointense to muscle on T1W/PDW images (Fig. 6.107a) and homogeneously or inhomogeneously hypointense to fat on conventional T2W FSE images (Fig. 6.107b), usually best seen in the axial plane

●● variable SI on FS T2W/STIR (Fig. 6.107c) with/without minor peripheral oedema and associated bursitis (Figs 6.107b, c)

●● they show variable enhancement following gadolinium, with ~50% showing little or no enhancement and the remainder showing marked enhancement

●● the diagnostic accuracy of MRI is almost 100%, while the reported sensitivity and specificity is 93% and 68%, respectively260

●● transverse dimensions are typically 3-9 mm, but are dependent upon scanning position:261 ● when imaged with the patient prone and the foot plantar-flexed (Fig. 6.107e), neuromas are on

average 2 mm wider

●● the flexor tendons: in the forefoot, the FDL tendons lie deep to the flexor FDB tendons (Fig. 6.108a): ●● at the level of the proximal interphalangeal joint (PIPJ), the FDB splits to straddle the FDL tendon, the

2 slips inserting into the base of the middle phalanx (Fig. 6.108b) ●● the FDL tendon continues distally to insert into the base of the distal phalanx (Fig. 6.108b)

●● the extensor tendons: the EDL tendons run in the dorsum of the foot with 4 tendon slips (Fig. 6.109a), each passing to the lateral 4 digits: ●● at the level of the MTPJs of the 2nd-4th toes, the EDL tendon is joined on its lateral side by the EDB

tendon slip (Fig. 6.109b)

●● the combined extensor tendon: runs over the dorsum of the 2nd-4th toes to join the extensor expansion (Fig. 6.109c)

●● at the level of the PIPJ, the extensor expansion divides into 3 parts (Fig. 6.109d): ● the central part inserts into the base of the middle phalanx (Fig. 6.109e), while the 2 lateral parts

converge to insert into the base of the distal phalanx

●● tendinosis: is characterised pathologically by angiofibroblastic hyperplasia, degeneration and necrosis with little or no associated inflammation

●● tenosynovitis: represents inflammation of the tendon sheath due to synovial inflammatory disorders, infection or mechanical irritation: ●● mechanical irritation may affect the FHL tendon between the sesamoid bones, where it is subject to

repetitive impact and may also occur under the base of the 1st MT bone, where the FHL and FDL tendons cross at the knot of Henry

●● hammer toe or cross toe deformities and injuries to the plantar plate can often predispose to FDL tenosynovitis ●● stenosing tenosynovitis: results from chronic inflammation leading to fibrosis and tendon entrapment ●● tendon rupture: occurs in tendons weakened by degeneration, repetitive microtrauma, or associated

with systemic disorders such as DM, crystal deposition diseases and inflammatory arthritides: ●● rupture of a normal tendon: is caused by laceration or a sudden traction injury, such ruptures being partial

or complete ●● MRI findings:

●● tendinosis: fusiform or diffuse tendon thickening, with mild SI abnormality on T1W/PDW images and increased T2W SI in the presence of mucoid degeneration

●● tenosynovitis: normal tendon morphology with increased fluid within the tendon sheath (Figs 6.110a, b) and tendon sheath enhancement following contrast

●● stenosing tenosynovitis: thickening of the tendon or tendon sheath due to fibrosis, increased fluid within the tendon sheath and tendon sheath enhancement following contrast (Fig. 6.110c)

●● tendon rupture: partial (Fig. 6.110d) or complete tendon discontinuity with intervening and surrounding oedema (Fig. 6.110e) and haemorrhage

●● patchy bone marrow SI: with reduced T1W and increased FS T2W FSE/STIR SI is a normal finding in children’s feet, reported to occur in 63% of symptomatic and 57% of asymptomatic children263

●● it is most commonly seen in the calcaneus (54%), talus (35%) and navicular (35%) bones, commonly at the endosteal surface

●● these changes are typically seen before the age of 16 years, and are believed to represent residual red marrow, or physiological stress related to normal skeletal growth

●● MRI findings: ●● focal or confluent areas of reduced SI on T1W and increased SI on FS T2W/STIR (Figs 6.111a, b),

which may be bilateral and symmetrical

●● Kohler’s disease: refers to osteochondrosis of the tarsal navicular, which is classically seen in boys between the ages of 3-10 years and is a self limiting condition, resolving with rest: ●● stress/trauma results in medial foot pain and swelling, which is bilateral in 25% of cases

●● other bones affected: include the medial cuneiform in young boys and the posterior calcaneal apophysis (Sever’s disease)

●● ON: may affect anywhere in the foot or ankle and is described in those receiving long-term corticosteroid treatment: ●● common sites include the talar dome, navicular and 2nd or 3rd metatarsal heads

abnormalities ●● MRI findings:

●● Kohler’s disease: reduced SI on T1W and increased SI on T2W images in the ossified navicular, with a normal appearance of the surrounding cartilage (Figs 6.112a, b)

●● Sever’s disease: oedema adjacent to the calcaneal apophysis (Figs 6.112c, d)

●● ON: of the talar dome in children manifests similarly to other sites in the skeleton: ● focal subchondral marrow oedema in the early stages ● progressive ON results in subchondral linear low SI on all pulse sequences with surrounding marrow

oedema ● late stages: manifest as diffuse sclerosis, fragmentation and collapse

●● congenital club foot (talipes equinovarus): is classified into 4 types: ●● teratologic, syndromic, positional and congenital

●● congenital: is the commonest type with a reported prevalence of 1:1000 live births, being more common in males and bilateral in 50% of cases

●● pathologically: abnormalities include lateral rotation of the talus, talar and calcaneal equinus, medial rotation of the calcaneus, medial subluxation of the navicular and cuboid, and soft-tissue contractures

●● MRI may be valuable for preoperative evaluation since it demonstrates the position of the unossified tarsal bones and intertarsal joints

●● MRI findings: ●● reduction of the talocalcaneal angle in both axial (normally 20-40°) and sagittal (normally 35-50°) planes ●● mild dorsal displacement of the navicular

●● flatfoot: is a term that includes both flexible and rigid flattening of the longitudinal arch of the foot ●● hindfoot deformity: includes valgus rotation of the calcaneus on the talus, resulting in vertical rotation of the

talus ●● ligamentous laxity contributes to flexible flatfoot (planovalgus foot) and may be considered a normal variant

●● rigid flatfoot: can be either acquired or congenital: ●● acquired rigid flatfoot: may be due to tarsal coalition with associated peroneal spasm, or cerebral palsy ●● congenital rigid flatfoot: in its most severe form is due to congenital vertical talus, in which case the

talus is vertically aligned to the calcaneus, the navicular is dorsally dislocated and the calcaneus is plantar flexed

●● MRI will demonstrate the precise orientation of the talus when it is still unossified

●● soft-tissue masses: of the foot and ankle may be non-neoplastic, neoplastic benign or neoplastic malignant ●● ~8% of all benign masses and 5% of all malignant masses (sarcomas) arise in this location ●● non-neoplastic lesions: ganglia, bursae and Morton’s neuroma are the commonest ●● benign neoplastic lesions: excluding tumours of the skin, the commonest benign lesions are plantar

fibromatosis, giant cell tumour of tendon sheath (GCTTS), pigmented villonodular synovitis (PVNS), aggressive fibromatosis, lipoma and haemangioma

●● malignant lesions: excluding skin tumours, synovial sarcoma is the commonest ●● the imaging features of these lesions are as described elsewhere (Chapter 7)

●● ganglia (ganglion cysts): represent tumour-like lesions that arise due to myxoid degeneration of connective tissues and are therefore related to tendons, ligaments, joint capsules and aponeuroses, and do not communicate with adjacent joints

●● they are usually detected in young adults and are slightly more common in women ●● pathologically: they are round, oval or lobular cystic lesions filled with mucinous fluid and surrounded by a

fibrous capsule, commonly with internal fibrous septa ●● clinically: many ganglia are asymptomatic, but depending upon their location, they can result in sinus tarsi

syndrome (Figs 6.70c, d) or tarsal tunnel syndrome (Figs 6.78a, b) ●● in a large study of ankle and foot ganglia:271 ~42% of all clinically suspected soft-tissue masses were ganglia,

with a reported prevalence of 5.6% and 0.4% for masses around the ankle and foot, respectively: ●● the commonest locations were the sinus tarsi/canal (34%), the Lisfranc joint (23%), the cuneonavicular

joint (12%), the tarsal tunnel (12%), the talonavicular joint (9%), the EDL tendon (8%), the distal tibiofibular joint (8%) and the calcaneocuboid joint (7%)

●● MRI findings: ●● well-defined oval, round or multi-lobulated masses with internal fluid SI characteristics, being

hypointense to muscle on T1W images (Fig. 6.113a), mildly hyperintense on PDW FSE images (Fig. 6.113b) and markedly hyperintense on T2W FSE (Fig. 6.113c) and FS T2W FSE/STIR images

●● following contrast, rim and septal enhancement is seen

●● the medial malleolar bursa: is an adventitial bursa that may develop over the medial malleolus in response to abnormal pressure from footwear that closely approximates the ankle

●● in asymptomatic individuals: the soft tissues around the medial malleolus show normal subcutaneous fat in 80% of cases or mild oedematous changes, which measure <2 cm in dimension and show no mass effect

●● in symptomatic patients: a discrete mass with fluid SI characteristics can be seen in 60% of cases, representing an adventitial medial malleolar bursa, with dimensions of up to 6 × 3 × 2 cm ●● alternatively, poorly-defined extensive soft-tissue oedema may be seen (Fig. 6.114)

●● MR assessment: of the post-operative ankle and foot requires a detailed knowledge of the primary diagnosis, the surgical treatment undertaken, the time interval since surgery, the current clinical complaints and a knowledge of the range of normal post-operative MR appearances

●● technical considerations: reduction of metallic artefact can be achieved by use of SE or FSE imaging (possibly with the addition of gadolinium contrast), STIR sequences and avoidance of GRE and frequency-selective FS sequences

●● other technical aspects: such as FOV, matrix, slice thickness and imaging planes are as for standard ankle and foot imaging

●● aims of tendon repair: are to produce a union of adequate tensile strength and rapid restoration of gliding function

●● tendon repair: may be by suturing of the tendon ends, or the interposition of a graft if tendon lengthening is required: ●● options for autograft: include the plantaris, peroneus tertius or peroneus brevis tendons (PBT) for

relatively long grafts, and portions of the EDL, EDB or EHB tendons for shorter grafts ●● the diameter of the donor tendon should match that of the repaired tendon as closely as possible to reduce

formation of adhesions ●● the graft should appear identical to the recipient tendon by 10-12 weeks

●● Achilles tendon: repair may be either open or percutaneous, the latter recommended for recreational as opposed to high level athletes, due to the slightly higher re-rupture rate: ●● partial tears or small (<3 cm) complete tears can be repaired by end-end suture anastomosis ●● complete tears with a 3-6 cm gap can be repaired using an autogenous tendon-graft flap, while complete

tears with >6 cm gap can be repaired using either a free tendon graft or a synthetic graft (carbon or Marlex mesh)

●● tendon lengthening: may be performed in diabetics with foot ulceration to increase the range of dorsiflexion and reduce plantar pressure, this being achieved using a Z-plasty technique

●● for Haglund’s syndrome: surgery requires removal of the posterosuperior bony calcaneal prominence and adventitial bursa, debridement of the tendon and re-attachment to the calcaneus

●● MRI findings: ● an increased FOV should be used to include the musculotendinous junction ● at 1 year post-repair: the tendon shows generalised thickening and moderate heterogeneity of SI

(Figs 6.115a, b), with tendon oedema, tendon defects and peritendinous reactions (Fig. 6.115c) being seen in a minority of cases

● augmentation of Achilles tendon repair may be identified by an alteration in the course of the tendon used for augmentation, such as the FHL (Figs 6.115d, e)

● tendon defects or re-tears: appear as focal, intratendinous regions of increased SI on T2W or PDW images

● other post-operative complications include: infection, sural nerve injury and tendon ossification: – tendon ossification: appears as areas of marrow SI within the tendon which may result in tendon

dysfunction and predispose to tendon re-tear

●● tibialis anterior: surgical repair is recommended for young/middle-aged patients who present within 3-4 weeks of injury: ●● with early presentation and a small tendon gap, end-to-end repair is performed ●● with a larger gap a tendon graft may be used, options including free tendon grafts from EDL or peroneus

brevis, or a sliding tendon lengthening using a split portion of the intact proximal TAT, or suturing the proximal tendon stump to the EHL tendon

●● extensor hallucis longus (EHL): ruptures/lacerations may be treated surgically by direct end-to-end repair, or in the case of extensive tendon retraction, by a free tendon graft from EHB

●● tibialis posterior (TPT): ruptures are usually secondary to acute/chronic stress on an already degenerate tendon, usually posterior to the medial malleolus and resulting in acquired flatfoot deformity in the adult

●● TPT dysfunction:278 can be managed by primary repair or tendon grafting, with direct suturing of longitudinal splits or tendon reinforcement in the case of large defects, the latter by augmentation with the FDL or a portion of the tibialis anterior tendon (Cobb procedure): ●● the resulting flatfoot deformity requires correction using a variety of techniques, including triple

arthrodesis (Fig. 6.116a) or calcaneal osteotomy (Figs 6.116b, c)

●● peroneal tendons: chronic longitudinal peroneus brevis tears can be repaired, together with treatment of any associated predisposing bony causes, including resection of a sharp posterior fibular ridge, deepening of the retromalleolar fossa (Figs 6.117a, b) and/or reconstruction of the superior peroneal retinaculum, in associated subluxation/dislocation: ●● in the presence of a complete tendon disruption, surgical repair can be achieved using a plantaris graft or

attachment of the proximal tendon end to the peroneus longus tendon ●● complete rupture of the peroneal tendons can be treated by tenodesis to the cuboid/calcaneus ●● recurrent dislocation of the peroneal tendons: may be treated by deepening of the retromalleolar fossa,

tenoplasty or bone block

●● lateral ankle ligament repair: is performed in patients with ankle instability following recurrent inversion injury and who have failed conservative therapy

●● surgical options: include direct ligament repair and a variety of procedures using the peroneus brevis tendon

●● direct ligament repair: the Brostrom procedure involves suturing of the 2 ends of the ATFL, which may be reinforced by the adjacent peroneus brevis tendon: ●● MRI findings: suture anchors/artefact anterior to the lateral malleolus (Figs 6.118a, b), with thickening

of the anterior capsule and repaired ATFL (Fig. 6.118c) ●● direct repair of the CFL: is also described, possibly augmented by the lateral extensor retinaculum, the

lateral talocalcaneal ligament or periosteal flaps ●● procedures involving the PBT include:

●● PBT rerouting: called a modified Evans procedure, the PBT is transected proximally, passed through a surgically created oblique fibular tunnel, then re-attached at the proximal transection site:

● MRI findings: suture artefact is seen at the proximal PBT re-attachment site together with an oblique (from superoposterior to antero-inferior) fibular tunnel containing the hypointense PBT

●● PBT loop: also called the Lee procedure, this involves proximal transection of the tendon, with the free tendon end passed through a horizontal fibular tunnel, looped around the lateral malleolus and sutured back upon itself:

● the Watson Jones procedure: is a modification in which 2 fibular tunnels and a talar tunnel are also present

● MRI findings: suture artefact at the PBT anastomosis site just anterior to the lateral malleolus with a horizontal fibular tunnel containing the PBT loop, together with suture artefact at the proximal tendon transection site, where the PBT is sutured to the adjacent PLT

●● PBT split and re-routing: also termed the Chrisman-Snook procedure, the PBT is split longitudinally, with half of the tendon separated distally from the muscle, passed posteriorly through the talar periosteum, then through a horizontal fibular tunnel, then deep to the calcaneal periosteum, finally directed anteriorly and sutured upon itself near the 5th MT base, thus serving to repair both the ATFL and CFL:

● MRI findings: suture artefacts are seen at the lateral surfaces of the talus and calcaneus, where the tendon is passed subperiostially, and at the anastomosis site at the 5th MT base, with an associated horizontal fibular tunnel

●● plantar fascia release (fasciotomy): is performed for resistant plantar fasciitis, and can be achieved either through an endoscopic technique or an open procedure, with success rates of 90-95%

●● these procedures aim to transect ~80% of the medial plantar fascia, since complete transection can result in loss of the longitudinal arch and damage to the nerve supply to abductor digiti minimi

●● MRI findings: ●● following fasciotomy: several appearances of the plantar fascia can be seen, with a persistent defect at the

fasciotomy site being present in ~20% of cases ●● the commonest asymptomatic post-operative finding at 1 year is irregular thickening of the fascia,

typically to 2-3 times normal, with no oedema either within or around the fascia but residual areas of intermediate internal SI on PDW images, the features being the same for both open and endoscopic techniques

●● imaging findings in patients with persistent post-operative pain can be divided into 3 groups: ● those with features of recurrent plantar fasciitis, manifest as intra-and perifascial oedema ● those with features of midfoot instability due to loss of the supportive effect of the fascia on the

longitudinal arch, resulting in an increased incidence of tears to the TPT, PBT and PLT, together with mid-tarsal OA

● those with acute rupture of the plantar fascia at or near the fasciotomy site

●● surgery for tarsal tunnel syndrome: is required in cases of failed conservative treatment and consists of division of the flexor retinaculum, with mobilisation of the medial and lateral plantar nerves and the fibrous origin of abductor hallucis

●● surgical outcome is optimal when a specific mass lesion is the cause of symptoms

●● MRI findings: ●● scarring of the subcutaneous fat and fascia along the medial aspect of the foot adjacent to the medial

malleolus ●● causes of failed surgery include re-growth of the flexor retinaculum, recurrent ganglia or fibrosis

impinging on the nerves, which can be demonstrated with the use of post-contrast studies

●● arthrofibrosis: of the foot and ankle refers to pain and stiffness that does not allow a functional range of movement, and is due to adhesions or contractures of the joint

●● surgery and trauma are the commonest causes, with infection and CRPS also representing potential risk factors: ●● anterior capsular fibrosis is often seen following ankle arthrotomy for internal fixation of fractures ●● posterior ankle capsular fibrosis is described following posterior ankle impingement surgery ●● MTPJ arthrofibrosis: is described at the 1st MTPJ following HV surgery and at the lesser MTPJ following

Weil osteotomy ●● abnormal fibrous tissue proliferation is seen, which may be localised or diffuse, and may be intra-or extra-

articular ●● patients are often managed conservatively, although arthroscopic or open debridement may be required ●● MRI findings:

●● ankle arthrofibrosis: intermediate SI capsular and pericapsular thickening (>3 mm at the ankle joint) on T1W/PDW images (Fig. 6.119) is usually seen within the first 6 months, which subsequently becomes of lower SI:

● however, ankle capsular thickening is also described in asymptomatic subjects ●● posterior subtalar joint arthrofibrosis: typically involves the anterior capsule with focal capsular thickening

on sagittal PDW images, with/without oedema in the adjacent sinus tarsi ●● MTP joint arthrofibrosis usually involves the dorsal capsule

●● Morton’s neuroma: resection is associated with persistent pain in up to 35% of cases: ●● imaging appearances consistent with a recurrent Morton’s neuroma are seen in 50% of symptomatic

individuals post-operatively, but can also occur in up to 26% of asymptomatic subjects ●● recurrent Morton’s neuroma-like abnormalities are often larger in symptomatic cases than in

asymptomatic individuals (mean transverse diameter 6.8 mm vs. 5 mm)

●● cartilage repair: procedures used to treat osteochondral lesions in the talar dome are similar to those in the knee (see Chapter 5) and include local marrow stimulation techniques, biological tissue grafts and cell-based therapies, all of which are reported to have good clinical outcomes at mid-term follow up