The Wrist and Hand

Introduction ●● the radiocarpal joint: is formed by the articulation between the distal radius and the adjacent scaphoid and

lunate ●● the ulnocarpal joint: is formed by the distal ulna, TFCC and adjacent lunate and triquetrum

●● the distal radius: has 2 concave depressions in its articular surface that articulate with the scaphoid and lunate (Fig. 3.6a): ●● the scaphoid fossa is triangular in shape and the lunate fossa is rectangular

●● radial inclination: describes the angulation of the distal radial articular surface with reference to a line drawn perpendicular to the long axis of the radius on an AP radiograph (coronal MRI) (Fig. 3.6b), with normal values being ~15-35° (mean ~23°)

●● palmar tilt: describes the volar angulation of the distal radial articular surface with reference to a line drawn perpendicular to the long axis of the radius on a lateral radiograph (sagittal MRI) (Fig. 3.6c), with normal values being 0-20° (mean 12° in women and 9° in men): ●● any degree of dorsal tilt is considered abnormal

and 3rd extensor tendon compartments (Fig. 3.6e)

●● the distal ulna: comprises the ulnar head and ulnar styloid (Figs 3.7a-c) ●● ulnar variance: also termed radio-ulnar index or Hulten variance, refers to the relative lengths of the distal

radius and ulna: ●● neutral variance: both articular surfaces are of equal length ●● positive variance: the ulnar articular surface is distal to the radial articular surface (Fig. 3.7d) ●● negative variance: the ulnar articular surface is proximal to the radial articular surface (Fig. 3.7e)

●● ulnar variance: is dependent upon forearm position, being greatest with forearm pronation and the wrist gripped, and least with forearm supination

●● MRI is the most accurate technique for assessing ulnar variance, although the comparison to PA radiographs is not statistically significant28

●● MRI of distal radial fractures: may show features not evident on radiography, including: ●● extension into the DRUJ and radiocarpal joint (Figs 3.8a, b) and occult carpal bone fractures ●● soft-tissue injury: is reported in 48% of cases, including scapholunate ligament rupture (Fig. 3.8c), TFCC

rupture (Fig. 3.8c), extensor carpi ulnaris (ECU) tenosynovitis (Fig. 3.8d) and dorsal radiocarpal ligament rupture

●● tendon entrapment: is reported in 1.3% of distal radial fractures, with extensor tendon entrapment following volar displacement being more common than flexor tendon entrapment following dorsal displacement30

●● MRI can demonstrate extensor tendon sheath fat-fluid levels in radiographically occult distal radial fractures31

●● with clinical suspicion of a wrist fracture on normal radiographs, occult fractures are identified on MRI in ~62% of cases, the distal radius being the commonest location (Figs 3.8e-h)32

●● gymnast’s wrist: is a general term describing pain due to distal radial overuse from repetitive shear or compression stress, most commonly resulting from a non-displaced Salter-Harris type 1 physeal injury in young athletes:

●● aetiology: possibilities include multiple physeal microfractures or localised ischaemic insult to the growth plate causing distal radial physis growth disturbance

●● results in localised separation of the epiphysis from the metaphysis ●● delayed growth may result in permanent loss of length of the affected radius, which less commonly may be

asymmetric, giving rise to an acquired Madelung deformity (see below) ●● MRI findings:35

●● abnormal signal intensity (Figs 3.9a, b) and widening of the lateral margin of the distal radial physis

●● Madelung deformity (MD): represents a developmental growth disturbance due to asymmetrical premature closure of the medial distal radial physis, which may be idiopathic, associated with a variety of syndromes (e.g. Léri-Weill dyschondrosteosis), or post-traumatic in aetiology

●● clinically: idiopathic (primary) MD presents in childhood/adolescence with wrist pain, deformity and weakness

●● MRI findings: ●● a fixed pronated deformity of the distal radius, with a physeal bar that bridges the metaphysis and epiphysis

of the radius on the volar aspect of the ulnar facet (Fig. 3.10a) ●● ulnar and volar curvature of the radius ●● positive ulnar variance with dorsal prominence of the ulnar head (Figs 3.10b, c) ●● ligamentous abnormalities include: an anomalous volar ligament and hypertrophy of the short radiolunate

(so called Vickers) and volar radiotriquetral ligaments ●● extensor tendon rupture may occur in chronic cases

●● the wrist ligaments: can be classified as being extrinsic or intrinsic, volar or dorsal ●● extrinsic ligaments: originate in the forearm and insert into the carpal bones:

●● they are intracapsular but extrasynovial and are enveloped by a continuous layer of capsule superficially while their deep surfaces are coated by synovium

●● they typically have a striated appearance, with alternating bands of high and low SI ●● the intrinsic ligaments (see later): are confined to the carpus and represent capsular thickenings, appearing as

hypointense bands on all MR pulse sequences

●● the volar extrinsic ligaments: are considered to be the most important stabilisers of the wrist joint, preventing ulnar translocation of the carpus and supporting the intra-articular ligaments in controlling carpal motion

●● the radioscaphocapitate ligament (RSCL): is the most radial and superficial of the extrinsic ligaments: ●● an oblique ligament originating from the volar surface of the radial styloid (Fig. 3.11a), running across

the scaphoid waist to insert into the head of the capitate (Fig. 3.11b)

●● it is located radial to the radiolunotriquetral ligament (RLTL), from which it is separated by a normal interligamentous sulcus

●● it also inserts via a fibrous band into the volar aspect of the distal pole of the scaphoid and plays an important role in preventing rotatory subluxation of the scaphoid

●● it is well seen on coronal 3D-GRE images performed at 1 mm slice thickness ●● RLTL: arises from the radial styloid on the ulnar side of the RSCL (Figs 3.11b, c) and runs obliquely

across the wrist, inserting into the volar ridge of the lunate and distally into the volar surface of the triquetrum: ●● it is a major stabiliser of the wrist and also inserts into the volar surfaces of the interosseous scapholunate

and lunotriquetral ligaments at the ‘confluence zone’ ●● it is routinely visualised on coronal and sagittal images (Fig. 3.11d)

the lunate ●● it is a palmar capsular thickening which stabilises the lunate

●● the radioscapholunate ligament (RSLL): is the deepest volar extrinsic ligament, arising from the volar rim of the radius at the junction of the scaphoid and lunate fossae: ●● superficial fibres insert into the scaphoid and lunate bones and deep fibres merge with the scapholunate

ligament (SLL) ●● rather than representing a true ligament, it is considered to be a neurovascular pedicle supplying

the scapholunate ligament,42 accounting for its normal increased SI compared to other wrist ligaments

●● the ulnolunate ligament (ULL): originates from the mid-third of the TFC/volar radio-ulnar ligament and inserts into the volar aspect of the lunate (see later)

●● the ulnotriquetral ligament (UTL): originates from the mid-third of the TFC/volar radio-ulnar ligament and inserts into the volar invagination of the triquetrum (Fig. 3.11e)

●● the dorsal extrinsic ligaments: comprise the RLTL and the UTL ●● the RLTL: is a dorsal capsular thickening composed of 1-3 fascicles, arising from Lister’s tubercle (84% of

cases) or the radial styloid and inserting into the dorsal rim of the triquetrum (Fig. 3.12a), but also into the lunate: ●● it is usually well visualised on thin section 3D coronal imaging and functions as a secondary stabiliser of

the carpal bones, helping to support the lunate dorsally ●● the UTL: arises from the dorsal radio-ulnar ligament and extends to the dorsal aspect of the triquetrum

(Fig. 3.12b)

●● ligament sprains: are a common cause of wrist pain after injury, frequently associated with scaphoid or distal radial fractures

usually associated with lunotriquetral ligament tears and ulnar-sided wrist instability ●● dorsal extrinsic ligament tears: are seen in ~37% of scaphoid fractures49 ●● MRI findings:

●● ligament sprains: manifest as slight diffuse increased SI with surrounding soft-tissue oedema (Figs 3.13a, b) ●● ligament disruption: manifests as thickening, thinning, elongation or absence, with increased T2W SI and

surrounding fluid ●● focal partial tears: manifest as swelling, heterogeneous SI, irregular fraying or partial discontinuity42 ●● chronic injuries: may be associated with ganglion cyst formation

●● MR arthrography findings: ●● leak of injected contrast medium through defects in the ligament/capsule (Fig. 3.13c)

The Collateral Ligaments ●● the radial collateral ligament (RCL): arises from the tip of the radial styloid and inserts into the radial aspect

of the scaphoid waist and flexor carpi radialis (FCR) tendon (Fig. 3.14) ●● the ulnar collateral ligament (UCL): is not a prominent structure and merges with the tendon sheath of ECU,

thus forming part of the TFCC: ●● it arises from the ulnar styloid and inserts into the triquetrum or pisiform ●● it not clearly visualised separately on MRI, but is frequently seen on MR arthrography at both 1.5T and 3T41

●● the collateral ligaments are not considered to be as functionally important as the volar and dorsal extrinsic ligaments of the wrist46

●● the TFCC: stabilises the DRUJ and supports the compression load of the carpal bones ●● components of the TFCC include:

●● the central (articular) disc TFC ●● the volar and dorsal radio-ulnar ligaments ●● the volar ulnolunate and volar ulnotriquetral ligaments ●● the meniscal homologue (ulnocarpal meniscus or ulnomeniscal homologue) ●● the ulnar collateral ligament and tendon sheath of ECU

●● the TFC: appears on MRI as a low SI structure with smooth margins located between the distal ulna and carpus, and is optimally demonstrated at 3T: ●● on coronal images: it appears triangular with its apex at the radial attachment (Figs 3.15a, b):

● it is attached to the hyaline cartilage of the distal radius, resulting in a normal increased SI zone between it and the bone (Figs 3.15a, b)

●● on sagittal images: it appears biconvex with thicker peripheral margins (Fig. 3.15c) ●● on axial images: it appears triangular with its apex at the ulnar styloid (Fig. 3.15d) ●● the TFC originates from the ulnar border of the distal radius between the sigmoid notch and distal

articular surface, where it separates the radiocarpal joint from the DRUJ ●● it extends to the ulnar styloid, where 2 types of attachment are described:

● 1: to both the fovea at the base of the ulnar styloid and the tip of the ulnar styloid (Fig. 3.15e); this type of ulnar attachment is sometimes referred to as the triangular ligament, with the foveal and styloid attachments described as the proximal and distal laminae of the triangular ligament, respectively

● 2: less commonly, a broad-based striated fascicle attaching along the length of the ulnar styloid ●● the ulnar attachment of the TFC normally has a striated appearance on T2W images (Fig. 3.15e) owing

to its composition of a mixture of collagen fibres and vascular connective tissues, which could mimic a sprain or a partial tear:56

● it may be obscured by intervening loose vascular connective tissue (termed the ligamentum subcruentum), which manifests as relatively increased SI on T1W (Fig. 3.15f) and T2W images (Fig. 3.15g)

●● the dorsomedial margin of the TFC is also attached to the ECU tendon and meniscus homologue by fibrous bands

●● the TFC is thicker (~5 mm) at its margins than centrally (~2 mm), with the thickness being inversely proportional to ulnar length (Fig. 3.15h)

●● the thickened dorsal and volar margins of the TFC are also referred to as the dorsal (Fig. 3.16a) and volar radio-ulnar ligaments (Fig. 3.16b), which stabilise the DRUJ:

● they are best visualised on axial imaging as low SI bands that attach to the fovea and styloid tip

●● the volar ulnolunate and ulnotriquetral ligaments are best visualised on coronal images ●● the meniscal homologue: lies on the volar side of the wrist, arising from the dorsoulnar corner of the

radius, in common with the dorsal radio-ulnar ligament and inserting into the triquetrum, separating the pisotriquetral joint from the radiocarpal joint: ●● it is best demonstrated on coronal images (Fig. 3.16c), but MR arthrography (Fig. 3.16d) may offer

better visualisation than conventional MRI57 ●● the prestyloid recess: is an extension of the radiocarpal joint lying just distal to the ulnar styloid, representing

a fluid-filled space located between the TFC and meniscal homologue (Figs 3.16c, d) ●● changes in morphology of the TFCC occur between neutral, supine and prone positioning:58,59

●● no change occurs in the shape of the TFC or radial portions of the radio-ulnar ligaments ●● the TFC is horizontal in the neutral position and tilted to align with the proximal carpal row in pronation

and supination (Fig. 3.16e) ●● the ulnar attachment of the TFC changes orientation from coronal in neutral to sagittal in supination and

pronation ●● the meniscal homologue appears smaller in supination and pronation ●● the ECU tendon is centred in its groove in neutral and pronation, but subluxes in supination by up to 2 mm

●● asymptomatic degenerative change: is a common finding with increasing age, being seen in 38-55% of individuals in the 3rd-4th decades and 100% in the 6th decade: ●● it tends to affect the central portion of the articular disc (Fig. 3.16f) (a relatively avascular zone), and may

progress to a degenerative tear

●● asymptomatic communicating defects have been reported in 46% of wrists, with 69% being bilateral and most occurring on the radial side of the disc

●● non-communicating defects are reported in 27% of asymptomatic discs ●● degeneration manifests as intermediate SI on T1W SE/PDW FSE images without increased SI on

T2W/STIR images ●● a significant improvement in anatomical depiction of the components of the TFCC has been demonstrated at

3T compared with 1.5T imaging6

●● TFCC tears: manifest clinically as non-specific ulnar-sided wrist pain, crepitus and weakness: ●● in relation to sports injuries, they occur following a rapid twisting mechanism with ulnar loading, as seen

with racquet sports, golf and gymnastics, and may be associated with distal radial fractures ●● traumatic injury is also observed in forced axial loading to the wrist in an extension-pronation position

(fall on the outstretched hand), and is typically seen in those younger than 40 years of age ●● ulnar positive variance is an anatomical predisposing factor for TFCC injury

● IA: central perforation (Fig. 3.17a) ● IB: ulnar avulsion with/without distal ulnar/ulnar styloid fracture (Fig. 3.17b) ● IC: distal avulsion from the carpal attachment to the lunate or triquetrum ● ID: radial avulsion with/without sigmoid notch fracture

●● type 2: degenerative injury (represents the progressive stages of ulnocarpal impaction syndrome): ● IIA: TFC thinning and degeneration, predominantly on the ulnar side (Fig. 3.17c) ● IIB: TFC thinning and degeneration with lunate (Fig. 3.17d) or ulnar chondromalacia ● IIC: TFC perforation with lunate or ulnar chondromalacia (Fig. 3.17e) ● IID: TFC perforation with lunate or ulnar chondromalacia and lunotriquetral ligament rupture

(described in 70% of cases) ● IIE: TFC perforation with lunate or ulnar chondromalacia, lunotriquetral ligament rupture and

osteoarthritis ●● degenerative defects are more common than traumatic defects

●● MRI findings: ●● no MRI features reliably differentiate degenerative from traumatic tears, the diagnosis being dependent

upon a history of acute injury, while positive ulnar variance may indicate a type 2 lesion (Fig. 3.17e) ●● TFC tears manifest as discontinuity and/or fragmentation of the normally hypointense TFC disc ●● traumatic tears (central perforations) occur most commonly on the radial side of the disc, 2-3 mm from

the radial insertion and are commonly slit-like (Fig. 3.17a) ●● intermediate SI on T1W (Fig. 3.17f) and high SI on T2W may be seen within the tear due to fluid

(Fig. 3.17g) ●● ulnar-side tears may be associated with fluid in the DRUJ (non-specific) (Fig. 3.17g) and proximal to

the prestyloid recess: ● they may then be associated with subluxation of the ulnar head

●● 3T MRI: is reported to have a sensitivity, specificity and accuracy of 100%, 86% and 90% respectively when compared to surgical findings:63

● direct comparison with 1.5T suggests 3T provides improved capability for detection of TFCC injuries64

● however, the sensitivity, specificity and accuracy for ulnar-side tears is lower and reported as 17%, 79% and 64% respectively when assessed at 1.5T,65 although sensitivity may be improved by imaging the wrist in maximal ulnar abduction

●● MR arthrography findings: ●● direct MR arthrography demonstrates hyperintense fluid within the tear on FS T1W images (Fig. 3.17h)

●● contrast extension into the DRUJ after radiocarpal injection, or in the radiocarpal compartment after DRUJ injection indicates a communicating full-thickness TFC tear

●● central TFC tears are detected with a sensitivity and specificity of ~95% and 100% respectively using 3D volumetric MR arthrography performed at 3T66

●● a cadaveric study has reported a sensitivity and specificity of 100% and 100% for detection of TFC tears at 3T MR arthrography63

●● ulnar impaction syndrome: is also known as ulnolunate abutment or ulnocarpal loading, and is caused by impaction between the ulnar head and the ulnar side of the carpus: ●● it is a degenerative condition most commonly occurring with positive ulnar variance, although

occasionally in the setting of neutral or negative ulnar variance ●● predisposing factors: include congenital positive ulnar variance or secondary positive ulnar variance due to:

●● distal radial fracture (Fig. 3.18a), premature closure of the distal radial physis or previous radial head resection

●● it is also seen with abnormal loading of the ulnar carpus, such as in gymnasts ●● clinically: it manifests with ulnar-side wrist pain, swelling and limitation of movement ●● MRI may be useful in establishing the diagnosis when radiographs are normal, as well as assessing the extent

of chondral wear, marrow oedema and associated soft-tissue involvement

●● MRI findings: ●● early: fibrillation of the ulnar head, lunate and triquetral articular cartilage ●● bone hyperaemia, manifest as marrow oedema in the ulnar head, ulnar aspect of the lunate (Fig. 3.18b)

and adjacent triquetrum (Fig. 3.18c), which may resolve following ulnar shortening ●● progression to marrow sclerosis (Fig. 3.18d) and subchondral cystic change (Figs 3.18c, e, f ), which

tends to be localised to the proximal ulnar side of the lunate as opposed to more generalised lunate involvement of Kienböck’s disease (see later)

●● degenerative tear of the TFCC (Figs 3.18e, f ) ●● end-stage: rupture of the lunotriquetral ligament

●● ulnar impingement syndrome: is caused by a short distal ulna, which impinges on the distal radius proximal to the sigmoid notch resulting in a painful pseudarthrosis

●● a short ulna is most commonly due to surgical resection of the distal ulna: ●● other causes include: negative ulnar variance or post-traumatic premature fusion of the distal

ulnar physis ●● clinically: it manifests as ulnar-side wrist pain, which is exacerbated by forearm supination and pronation ●● MRI findings:

●● a short ulna with impingement against the distal radius proximal to the sigmoid notch (Fig. 3.19a) ●● scalloping of the ulnar side of the distal radial metaphysis (Fig. 3.19a), with mild sclerosis or marrow

oedema (Fig. 3.19b) ●● shortening of the ulna may result in secondary deformity of the TFCC

●● ulnar styloid fractures: may be isolated or, more commonly, associated with distal radial fracture ●● symptomatic non-union of the ulnar styloid may result from:

●● loose body formation with irritation of the proximal ulnar side of the carpus ●● impingement of the ECU tendon or TFCC injury

●● 2 types of ulnar styloid non-union are described: ●● type 1 non-union: affecting only the tip of the styloid process, leaving the DRUJ and TFCC intact ●● type 2 non-union: the fracture occurs at the styloid base with disruption of the TFCC attachment (Palmar

type 1B lesion) resulting in DRUJ instability ●● MRI findings:

●● a non-united ulnar styloid fragment (Figs 3.20a, b) ●● chondromalacia of the ulnar-side of the carpus, notably the triquetrum, as well as associated TFCC and

DRUJ injuries ●● ECU tenosynovitis (Figs 3.20b, c)

●● ulnar styloid impaction syndrome: represents ulnar-sided wrist pain due to impaction between an excessively long ulnar styloid (>6 mm) and the adjacent triquetrum: ●● it is less common than ulnar impaction syndrome (see earlier) and is associated with negative ulnar variance

●● pathologically: single or repetitive trauma results in bone contusion, chondromalacia and synovitis: ●● a single traumatic event may result in dorsal triquetral fracture, while chronic impaction may produce

lunotriquetral instability ●● MRI findings:

●● a prominent ulnar styloid (Figs 3.21a, b) ●● chondromalacia of the ulnar styloid and adjacent triquetrum, with associated marrow oedema or

subchondral cysts (Fig. 3.21b) ●● lunotriquetral ligament tear ●● TFCC injury can occur (see earlier), and MR arthrography may be useful for evaluation

●● the carpus: comprises 2 rows of 4 bones each ●● the proximal row: comprises the scaphoid, lunate, triquetrum and pisiform (Figs 3.22a, b)

●● the distal row: comprises the trapezium, trapezoid, capitate and hamate (Figs 3.22c, d) ●● 3 smooth arcs are described with normal radiocarpal and intercarpal alignment:

●● 1: the proximal articular margins of the proximal carpal row ●● 2: the distal articular margins of the proximal carpal row ●● 3: the proximal articular margins of the distal carpal row

●● disruption of these arcs is seen with ligament rupture and carpal instability ●● the 2 carpal rows are separated by the mid-carpal joint, which is composed of 3 compartments:

●● laterally: the scaphotrapezoid-trapezial (tri-scaphe) and scaphocapitate (Fig. 3.23a) ●● centrally: the capito-lunate (Fig. 3.23b) ●● medially: the hamato-triquetral (Fig. 3.23b)

●● the central column: of the wrist is composed of the lunate and capitate: ●● with normal alignment: in the sagittal plane a line can be drawn through the long axis of the distal radius,

lunate, capitate and the third metacarpal (Fig. 3.23c) ●● the lunocapitate angle: is measured on sagittal images, being formed by the intersection of a line drawn along

the long axis of the lunate and a line drawn along the long axis of the capitate, the normal angle being <20° (Fig. 3.23d)

●● the scapholunate angle: is formed by a line drawn along the long axis of the scaphoid that intersects a line drawn along the long axis of the lunate: ●● it is assessed on separate sagittal MR images by adding the radiolunate (RL) and radioscaphoid

(RS) angles ●● the RL angle: is formed between a line drawn along the long axis of the radius and the long axis

of the lunate (Fig. 3.23e) ●● the RS angle: is formed between a line drawn along the long axis of the radius and the long axis

of the scaphoid (Fig. 3.23f) ●● the scapholunate angle is normally between 30-60°

●● carpal instability: can be determined by measurements of lunocapitate and scapholunate angles which lie outside these ranges, either in a volar or a dorsal direction

●● accessory ossicles: represent secondary ossification centres, which are distinct from the associated underlying bone and are usually congenital: ●● they may also be post-traumatic or degenerative in origin and can mimic fracture fragments or loose

bodies ●● ~ 20 different accessory ossicles are described in the wrist ●● the commonest are: the lunula, os styloideum, triangulare, epilunate, trapezium secondarium and os hamuli

proprium ●● the lunula: is located within the meniscal homologue (Fig. 3.24) and may be fused to the styloid process of

the ulna ●● the os styloideum:72,76 may result in the so called ‘carpal boss’, a bony protuberance on the dorsum of the wrist

for which the differential diagnosis is a degenerative osteophyte: ●● it is located between the bases of the 2nd and 3rd metacarpals and usually affects the dominant hand,

but is bilateral in 21% of cases ●● it has a reported prevalence of 8-26%, but is symptomatic in only 3% of individuals, in which case MRI

may show marrow oedema, surrounding fluid/joint effusion, an associated ganglion or bursa, extensor tendon subluxation, tendinopathy or rupture77

●● the ossicles may or may not be fused to the adjacent metacarpal base, and may simulate a dorsal ganglion ●● the triangulare: is located just distal to the ulnar fovea ●● the epilunate: lies at the dorsum of the lunate and projects into the joint, simulating a loose body ●● the trapezium secondarium: is located at the superomedial aspect of the trapezium ●● the os hamuli proprium: is located at the tip of the hook of hamate, being small with rounded contours

distinguishing it from a fracture, and may be associated with a hypoplastic hook of hamate

●● carpal coalition: represents a cartilaginous, fibrous or osseous fusion between 2 carpal bones, being either idiopathic or acquired: ●● idiopathic coalitions involve bones within the same carpal row, while acquired coalitions usually involve

bones in adjacent rows ●● lunotriquetral: is the commonest idiopathic coalition with a prevalence of ~0.1%, and may be classified into

4 types: ●● type 1: fibrous or cartilaginous coalition (Figs 3.25a, b)

●● type 2: incomplete osseous coalition with distal notch (Fig. 3.25c) ●● type 3: complete osseous coalition (Fig. 3.25d) ●● type 4: type 3 with associated carpal anomalies ●● widening of the scapholunate space is seen radiographically in ~50% of cases, and is considered to be

a normal variant, since arthrography shows an intact scapholunate ligament

●● capito-hamate: is second commonest carpal coalition (Figs 3.25e, f ) ●● pisohamate: is rare and involves abnormal union of the pisiform and hook of the hamate (Fig. 3.25g):

●● osseous coalitions may be prone to fracture, while fibrous coalitions may predispose to ulnar neuropathy78

●● clinically: carpal coalitions are usually asymptomatic, although type 1 coalitions may be painful: ●● they are much more common in the black population (prevalence ~10%) and in women, commonly being

bilateral52 ●● MRI findings:

●● osseous fusion: complete absence of joint space between the involved bones, with continuous bony trabeculae (Figs 3.25c, d, f-h)

●● partial fusion: reduced space between the involved carpal bones with either increased or decrease SI (Figs 3.25a, b) in the case of cartilaginous or fibrous coalitions respectively, and subchondral cystic changes (Fig. 3.25e)

●● lunate morphology: may be classified as type 1 or 2: ●● type 1: has classical anatomy with a single facet at the mid-carpal joint, which articulates with the capitate

(Fig. 3.26a) ●● type 2: has an additional medial facet that articulates with the proximal hamate (Fig. 3.26b) and is

referred to as the hamato-lunate facet, having a reported frequency of 44-73%:79 ● the facet is larger on the dorsal aspect (Fig. 3.26c) and may only be visualised on dorsal sections ● it is associated with a rounded proximal pole of the hamate (Figs 3.26b, c) and results in disruption of

the second carpal arc

●● clinically: type 2 lunate is commonly associated with degenerative change at the proximal pole of the hamate and can result in ulnar-sided wrist pain (see later)

●● on sagittal images, the volar surface of the lunate may appear irregular due to the insertion sites of various ligaments (Fig. 3.26d)

●● the pisotriquetral joint: is comprised of the articulation between the pisiform and triquetrum (Figs 3.27a, b) ●● musculotendinous structures related to the joint include:

●● the flexor carpi ulnaris (FCU) tendon: which inserts into the proximal and palmar aspect of the pisiform (Fig. 3.27c) and has a mean width and depth of 8.3 and 3.2 mm, respectively

●● the abductor digiti minimi (ADM) muscle: which may arise from the pisiform alone or also from the pisohamate ligament (Fig. 3.27d)

●● ligamentous structures related to the joint include: ●● the pisohamate ligament: which arises from the palmar aspect of the distal pisiform bone (64%) or the

radial aspect of the distal pole of the pisiform (36%) and inserts into the hook of hamate (Figs 3.27c, d) ●● the pisometacarpal ligament: which arises from the distal pisiform and extends to the bases of the 4th and

5th metacarpals, running adjacent to the hook of hamate (Fig. 3.27e)

●● the sheath of the ECU tendon: which blends with the dorsal carpal ligament (Fig. 3.27a) on the ulnar aspect of the pisiform

●● the pisotriquetral ulnar ligament: a capsular thickening on the ulnar-side of the joint, lying deep to the extensor retinaculum

●● the transverse carpal ligament: which covers the carpal tunnel, dividing into 2 components on the ulnar side (Fig. 3.27a):

● the ligamentum carpi palmare: which extends over the proximal portion of Guyon’s canal and blends with the FCU tendon

● the ligamentum flexorum: which forms the floor of Guyon’s canal and inserts into the pisiform bone ●● the articular surface and capsule (Fig. 3.27b):

●● normal lipping of the margins of the joint may occur, mimicking osteophytes ●● the proximal joint recess is smooth and round, measuring approximately 8 mm ●● the distal joint recess is smaller and lies parallel to the distal margin of the pisiform ●● the capsule communicates with the wrist joint in 82-88% of cases

●● the scaphoid: is the commonest injured carpal bone, accounting for ~80% of all carpal fractures ●● classically, it occurs due to a fall on the outstretched hand (FOOSH) resulting in tenderness in the anatomical

snuffbox ●● 70% occur through the waist (Fig. 3.28a), with 30% involving the proximal (Fig. 3.28b) or distal poles

(Figs 3.28c, d) ●● fracture of the waist: may be complicated by non-union (50%), avascular necrosis (AVN) of the proximal pole

(30%), carpal instability and OA ●● fracture of the proximal pole: has the greatest propensity for AVN (~100%)84 due to the distal entry point of

nutrient vessels and the retrograde intraosseous nature of the blood supply ●● chronic fracture non-union: is associated with the development of accelerated osteoarthritis of the wrist with

a predictable pattern of deterioration over time, commonly termed scaphoid non-union advanced collapse, or SNAC wrist: ●● stage 1 – degenerative changes at the radioscaphoid articulation ●● stage 2 – radioscaphoid and scaphocapitate joint involvement ●● stage 3 – additional involvement of the capito-lunate joint ●● the radiolunate articulation is consistently spared initially, but eventually is also involved

●● perilunate fracture dislocations: are uncommonly associated with scaphoid fractures, occurring usually in the context of high energy trauma

●● ~15-20% of isolated scaphoid fractures are radiographically occult, but can be identified on MRI (Figs 3.28e, f ),85 which is more sensitive and specific than scintigraphy

●● MRI findings: ●● acute: a low SI band at the fracture site (Fig. 3.28e) with surrounding hyperintense oedema on FS T2W

FSE/STIR images (Fig. 3.28f): ● oedema without an associated hypointense fracture line (Figs 3.28g, h) indicates bone contusion or

bone bruising and is thought to represent trabecular microfracture84 ●● non-union: manifests as the presence of a persistent low SI line on T1W and T2W images, which may also

indicate fibrous union (Figs 3.29a, b): ● a persistent fluid-filled hyperintense line on T2W images allows definitive diagnosis of non-union

(Fig. 3.29c) ●● AVN:83 definitive features include collapse and fragmentation:

● low SI within the proximal pole on T1W/PDW FSE images without collapse (Fig. 3.29d) may be seen in early AVN, but can also occur in revascularisation and new bone deposition in an ischaemic area

● oedema resulting in high T2W SI may be seen in the earliest stages, progressing to low SI when fibrosis or sclerosis supervene

●● post-contrast FS T1W SE MRI is reported to be superior to conventional MRI in assessment of AVN and scaphoid viability:

● the presence of enhancement (Fig. 3.29e) suggests viability of the fragment and correlates well with surgical findings and outcome (Fig. 3.29f)86

● dynamic contract enhanced (DCE) MRI may also be used, but its ability to provide additional information compared to standard post-contrast imaging for the assessment of viable versus non-viable bone based on time-intensity curves is uncertain87,88

●● Preiser’s disease: represents the rare idiopathic AVN of the scaphoid, which commences in the proximal pole: ● collapse of the proximal pole and sclerosis of the entire scaphoid are seen in more advanced cases89

●● hamate fractures: are of two main types, one localised to the hook and the other a fracture of the body, which is far less common

●● they account for ~2% of carpal fractures, being most commonly seen in athletes involved in racquet sports or baseball/golf, and are usually due to direct trauma against the handle of the racquet/golf club: ●● the non-dominant hand is frequently involved in baseball players and golfers, whereas the dominant hand

is usually affected in racquet sports ●● they are less commonly seen following a fall on the outstretched hand when there are often associated

dislocations of the 4th and 5th carpometacarpal joints ●● stress fracture: of the hook of the hamate has also been described in climbers91 ●● hook of hamate fractures: may be radiographically occult but can be demonstrated on axial or sagittal MR

images (Figs 3.30a-d) ●● associated soft-tissue injuries: include trauma to the flexor digitorum profundus (FDP) muscle, and if

diagnosis is delayed/overlooked, 5th finger flexor tendon rupture and ulnar nerve palsy

●● AVN of the lunate: also termed Kienböck’s disease or lunatomalacia, is considered to represent a repetitive traumatic phenomenon

●● clinically: it is typically seen in labourers in the 20-40 year age group and is more common in males, usually being unilateral, affecting the dominant hand and presenting with dorsal/central wrist pain and swelling: ●● it is often progressive, resulting in joint destruction within 3-5 years if untreated ●● it may be associated with ulnar minor variance, but is not limited to this patient group

●● infantile/juvenile lunatomalacia:94 is rare and considered the Kienböck’s disease of childhood, although the aetiology is not well understood: ●● differentiation is made on the basis of age, and in contrast to Kienböck’s disease, lunatomalacia in

childhood is generally self limiting with a good prognosis ●● Kienböck’s disease is classified into 4 stages as detailed below ●● MRI findings:

●● stage I: radiographs are normal while MRI shows marrow oedema (Figs 3.31a, b) ●● stage II: radiographs demonstrate sclerosis of the lunate while MRI shows marrow oedema and early

morphological changes (Fig. 3.31c) ●● stage III: radiographs and MRI demonstrate collapse of the lunate (Figs 3.31d, e) ●● stage IV: marked lunate collapse with secondary OA of the carpus (Fig. 3.31f) ●● in stage IV disease, T2W SI may be relatively normal ●● generalised marrow signal abnormality of the lunate, which initially starts with involvement of the

proximal radial aspect of the lunate as opposed to proximal ulnar-sided signal abnormality typically seen in ulnar impaction syndrome (see earlier)53

●● ulnar minor variance is present in ~78% of cases ●● contrast-enhanced MR: may help identify any viable bone (Fig. 3.31g), distinguishing partial from

complete necrosis and can influence choice of treatment, particularly in stage II but also in certain instances of stage III Kienböck’s disease93

●● marrow oedema: is reported in 36% of patients undergoing MRI for wrist pain ●● the commonest differential diagnoses include:

●● arthritis: focal OA (34%), ulnar impaction syndrome (9%), RA (8%), rarely septic arthritis, gout and scaphonlunate advanced collapse (SLAC)

●● occult fractures: most commonly of the scaphoid, but also other bones (Figs 3.32a-d) ●● AVN: usually of the lunate

●● stress injury of the lunate: is reported in junior tennis players, appearing as marrow oedema-like SI, usually in the distal part of the bone and without an associated fracture line (Figs 3.33a, b)96

●● hamato-lunate impaction: is associated with a type 2 lunate bone and hamato-lunate facet, which results in a higher prevalence of chondromalacia in the proximal hamate97

●● clinically: it may result in ulnar-side wrist pain ●● MRI findings:

●● a type 2 lunate (Figs 3.34a, b) ●● chondromalacia (Fig. 3.34b), with/without marrow oedema/cysts of the proximal hamate (Figs 3.34a, b)

●● pisotriquetral joint OA: is usually primary but may also occur secondary to a pisiform or triquetral fracture/ dislocation, or in association with racquet sports: ●● pain from the pisotriquetral joint occurs in 1% of cases following median nerve decompression

●● clinically: primary OA presents with ulnar-sided wrist pain, which is frequently bilateral and usually affects patients over the age of 50 years, especially females: ●● secondary OA, particularly in the context of overuse/racquet sports usually affects younger women

(mean age 30 years) ●● associated ulnar neuropathy is reported in approximately one-third of cases

●● dislocation of the pisiform: is rare and usually the result of direct trauma to the hypothenar eminence ●● pisotriquetral subluxation/sprain: is suspected when the joint space is wider than 4 mm, there is loss of

parallelism of the joint surface >20°, or there is proximal or distal displacement of the pisiform greater than 15% of the joint surface

●● MRI findings: ●● OA: marginal osteophytes with subchondral cyst formation, marrow oedema and joint effusion

(Figs 3.35a, b) ●● osteochondral loose bodies and synovial cyst formation in the hypothenar eminence, which may extend

into Guyon’s canal and compress the ulnar nerve ●● subluxation/sprain: widening of the joint space (Fig. 3.35c) and displacement of the pisiform (Fig. 3.35d)

●● the commonest causes of synovitis include: OA, trauma (including internal derangement), inflammatory diseases and infection

●● inflammatory arthritis-like changes:99 are not uncommonly seen on wrist MRI studies of asymptomatic individuals and include: ●● cystic or focal areas of marrow oedema-like SI in the carpal bones (Figs 3.36a-c):

● however, symptomatic lunate intraosseous ganglion has also been described101 ●● intraosseous blood vessels, most commonly in the capitate and lunate bones ●● notches at the bases of the 2nd MC, the capitate, hamate and triquetrum (Fig. 3.36d), which commonly

enhance following contrast ●● a small joint effusion and synovial enhancement in ~50% of cases

●● MRI findings: ●● those significantly associated with reactive carpal synovitis include:

● fluid in the pisotriquetral joint (Figs 3.37a, b), radial (Fig. 3.37c) and prestyloid recesses ● synovial enhancement following gadolinium (Fig. 3.37d) and pisotriquetral bone marrow oedema

(Fig. 3.37c) ● intraosseous ganglion: well-defined cystic lesion at the insertion site of the scapholunate ligament (SLL)

(Figs 3.37e, f ) with associated marrow oedema-like SI

●● complex regional pain syndrome (CRPS): also known as reflex sympathetic dystrophy (RSD), post-traumatic osteoporosis, Sudeck’s atrophy or reflex neurovascular dystrophy, is a chronic pain disorder of the sympathetic nervous system: ●● it most often occurs following trauma, burns, cancer or various central nervous system disorders and

usually results in diffuse involvement of the hand or foot ●● ~4% of subjects with conservatively managed wrist fractures develop CRPS within 4 months104

●● clinically: it presents with sustained regional pain, seemingly disproportionate to the original injury in duration and intensity: ●● hyperhidrosis and hypertrichosis, oedema, warmth, redness, stiffness of the skin and limitation of joint

movement ●● three clinical stages are recognised: the hypertrophic/warm stage, the atrophic/vascular instability stage and

the stabilised/cold stage ●● MRI findings:

●● patchy and diffuse foci of increased SI on FS T2W FSE/STIR images (Fig. 3.38) of affected bones and joints as well as soft tissues, including muscles and the overlying skin

●● periarticular oedema and marrow oedema is often seen related to tendon and ligament insertions ●● tenosynovitis, and fatty atrophy/infiltration of skeletal muscles in chronic cases ●● MRI has a relatively poor sensitivity (~43%) and moderate-to-high specificity (~78% at 8 weeks increasing

to 98% at 16 weeks after presentation) in the diagnosis of CRPS

●● the ligaments: responsible for stability of the carpus may be divided into intracapsular and intra-articular

●● intracapsular ligaments: represent those that are integrated in the capsular sheaths and may be either extrinsic (arising in the forearm and inserting in the carpus – see earlier) or intrinsic (arising and inserting in the carpus)

●● intra-articular (interosseous) ligaments: are deep and run transversely between carpal bones, including the scapholunate, lunotriquetral and mid-carpal ligaments

●● the volar intrinsic ligament: is also termed the arcuate (deltoid) ligament, and represents an array of fibres spreading across the scaphoid, capitate and triquetral bones (Figs 3.39a, b): ●● the ligament stabilises the distal carpal row on the proximal carpal row ●● it has an inverted ‘V’ configuration comprised of ulnar and radial limbs:

● the ulnar (capito-triquetral) limb: extends from the volar surfaces of the lunate and triquetrum to the neck of the capitate (Fig. 3.39a)

● radial (capito-scaphoid) limb: runs from the distal pole of the scaphoid to the capitate (Fig. 3.39a) ●● the dorsal intrinsic ligament: is composed of scaphotriquetral and triquetro-trapezoid components

(Fig. 3.39b): ●● it may be a single ligament (14% of cases), a branched structure (44% of cases) or 2 separate bands (38% of

cases) and arises from the dorsal tubercle of the triquetrum, fanning out to insert into the scaphoid and trapezium

●● rupture may result in an avulsion fracture from the triquetral insertion ●● these ligaments are optimally imaged at MR arthrography, but may also be identified utilising 3D MRI with

thin sections

●● the intrinsic ligaments: connect the carpal bones and separate the intercarpal compartments, comprising proximal and distal rows

●● the proximal row: unite the scaphoid with the lunate (scapholunate – SLL), and the lunate with the triquetrum (lunotriquetral – LTL)

●● the distal row: unite the trapezium with the trapezoid, the trapezoid with the capitate and the capitate with the hamate

●● the SLL and LTL: act to stabilise the wrist joint by linking and controlling motion of the proximal carpal row ●● the ligaments are deltoid or linear shaped structures with dorsal, central and volar components, being also

U-shaped and connecting the respective bones along their dorsal, proximal and volar margins ●● they separate the radiocarpal compartment from the mid-carpal compartment ●● the central portion (pars membranacea) attaches to cartilage, while the volar and dorsal segments attach

directly to bone ●● they have homogeneous low-intermediate SI on T1W SE/PDW FSE images but may show the presence of

normal central increased SI on T2W GRE images, which does not reach the same SI as fluid ●● their attachment to cartilage results in a line of increased SI between the ligament and bone, which may

mimic a tear ●● ligament degeneration may result in intermediate SI on T1W ●● asymptomatic perforations of the central portion are reported in ~50% of cases by the 8th decade of life,

while perforations of the dorsal portion are much more commonly symptomatic52 ●● SLL (Figs 3.40a-c):

●● the dorsal and volar components are band-like, with the dorsal component being the most important stabiliser

●● the membranous component varies in shape from volar to dorsal on coronal images: ● at its volar extent it is trapezoidal, centrally it is triangular whilst dorsally it is band-like56

●● it is optimally assessed and consistently visualised on a combination of coronal (Figs 3.40a, b) and axial (Fig. 3.40c) images

●● LTL (Figs 3.40d, e): ●● the dorsal and volar components are best assessed on axial imaging where they appear band-like

(Fig. 3.40e) ●● the membranous portion is best assessed in profile on coronal imaging:

● normal variations: triangular or deltoid shaped in >85%106 (Fig. 3.40d), being band-like or linear in only a minority

● internal moderate increased SI can be observed if the wrist is imaged in radial deviation,56 which should not be mistaken for degeneration or tear

●● improved visualisation of both ligaments is achieved with MR arthrography (Figs 3.40c, e, f )

●● SLL or LTL tears: may be partial (usually involving the volar portion) or complete, while tears of the central portion can be a normal asymptomatic ageing process

●● SLL tears: typically result from a dorsiflexion injury, such as a fall onto the pronated outstretched hand resulting in dorsal wrist pain, swelling, a popping sound with wrist motion and weakness of grip: ●● isolated SLL tears will not result in carpal instability in the presence of intact secondary stabilisers of

the scapholunate joint, which include the volar scaphotrapezio-trapezoidal ligament (STTL), the RSCL, the scaphocapitate ligament (SCL) and the FCR tendon

●● LTL tears: may represent the end stage of perilunate instability, may occur as an isolated injury due to an extension, radial loading mechanism, or may be part of the ulnocarpal impaction syndrome (stages IID or E of the Palmar classification of TFCC injury; see earlier): ●● isolated LTL tears will not result in carpal instability in the presence of intact secondary stabilisers of

the lunotriquetral joint, which include the extrinsic volar and dorsal RLTL ●● MRI findings:

●● non-visualisation of the ligament (rare) ●● fluid SI traversing the ligament on T2W images (highly specific) (Fig. 3.41a) and optimally assessed on

FS T2W FSE/STIR images (Fig. 3.41b) ●● abnormal ligament morphology: fraying, thinning, irregularity or elongation of the ligament with

a widened intercarpal space (Fig. 3.41c) ●● using the above criteria: an accuracy of 90% for SLL and 80% for LTL tears is reported ●● SLL and LTL tears are diagnosed with a sensitivity of 89% and 82% respectively at 3T, and specificity of

100% for both ligaments109 ●● in chronic cases, widening of the SL (Fig. 3.41d) or LT distances may be seen ●● FS T2W FSE axial images may aid assessment of tears involving the confluence zone, and partial tears

(Figs 3.41e, f ) ●● MR arthrography findings:

●● high SI contrast between the ends of the ruptured ligament with extension of contrast into the mid-carpal compartment (Fig. 3.41g)

●● with partial thickness tears, contrast outlines the abnormal morphology of the ligament ●● the presence of a joint effusion or MR arthrography may increase the sensitivity for the detection of tears,

●● ganglion cysts: are the commonest soft-tissue masses of the hand and wrist ●● clinically: they present as painless/painful masses with/without limitation of range of movement:

●● even very small ganglia can be symptomatic despite not being clinically apparent (Fig. 3.42a),113 while ganglion cysts are a common finding in asymptomatic individuals114

●● pressure on adjacent nerves from volar wrist ganglia can result in carpal tunnel (median) or Guyon’s canal (ulnar) syndromes

●● pathologically: ganglia result from degeneration of connective tissues related to tendon sheaths, ligaments and joint capsule: ●● ~30% are associated with internal derangement of the wrist, while 45% of ulnar-sided ganglia are

associated with TFCC tears and may extend in either a volar or a dorsal direction

●● 28% of radial-sided ganglia are associated with ligament tears (usually SLL), while a chronic tear of the dorsal band of the SLL may manifest as a scapholunate ganglion cyst

extensor compartments (Fig. 3.42d) ●● volar ganglia: account for 18-20% of wrist ganglia and are typically located between the 1st extensor

compartment and the FCR tendon (Figs 3.42e, f ): ●● approximately two-thirds arise from the radiocarpal joint and one-third from the scaphotrapezial joint

●● MRI findings: ●● homogeneous low/intermediate SI on T1W/PDW (Figs 3.42b, e, g) and high SI on T2W/STIR images

(Figs 3.42a, c, d, f ) ●● smooth, lobular margins with thin hypointense walls and fine internal septa ●● enhancement of the wall and septa following gadolinium (Fig. 3.42h), although very small cysts can

show almost uniform enhancement

●● carpal instability: is currently defined as ‘any disturbance of the static and dynamic balance of forces at the wrist under the conditions of daily living’

●● both intrinsic and extrinsic ligaments contribute to carpal stability and most instability patterns are caused by acute or repetitive wrist injuries: ●● hyperextension usually results in radial-side ligament tears, possibly with associated radial or scaphoid

fractures ●● rarely, hyperpronation injuries can result in ulnar-side ligament tears

●● non-traumatic causes: of carpal instability include AVN, systemic inflammatory conditions (e.g. RA, calcium pyrophosphate deposition (CPPD) disease), neurological disorders (syringomyelia) and congenital malformations such as Madelung deformity

●● the Mayo clinic classification: is the most commonly used system for carpal instability, where lesions are divided into dissociative (carpal instability dissociative [CID]) or non-dissociative (carpal instability non-dissociative [CIND]) types, which may be either static or dynamic71: ●● static instabilities: are those where carpal malalignment is demonstrated on radiographs ●● dynamic instabilities: are those which become manifest with different wrist positions or using stress

radiography or cine MRI116 ●● in CID: the elements of the proximal carpal row are malaligned relative to each other:

● CID includes scapholunate and lunotriquetral dissociation, and less commonly unstable scaphoid non-union as well as stages IIIb and IV Kienböck’s disease

●● in CIND: the proximal carpal row remains intact, but is dynamically or structurally misaligned with respect to the distal carpal row (mid-carpal instability, either dorsal or volar), or translated in an ulnar direction with respect to the distal forearm (radiocarpal instability/ulnar translocation):

● CIND usually implies injury to extrinsic carpal ligaments with intact intrinsic ligaments ●● they are anatomically differentiated into:

●● lateral: between the scaphoid and lunate, which may also produce dorsal intercalated segment instability (DISI) or SLAC

●● medial: between the lunate and triquetrum, which may also produce volar intercalated segment instability (VISI)

●● proximal: related to a distal radial fracture or massive radiocarpal disruption

●● scapholunate dissociation (SLD): presents with pain, swelling and tenderness over the dorso-radial aspect of the wrist and is associated with partial or complete tears of the SLL, usually from the scaphoid insertion

●● the SLL is the most commonly injured ligament in the wrist

●● SLD is divided into 4 stages: ●● stage I: predynamic, caused by a partial tear of the SLL with normal carpal function ●● stage II: caused by a complete SLL tear with instability manifest under load (dynamic) ●● stage III: caused by a complete tear of the SLL and secondary stabilisers resulting in instability at rest

(static), with volar flexion of the scaphoid (rotatory subluxation) (Figs 3.43a, b) and dorsal rotation of the lunate:

● the latter results in the DISI pattern, dorsal intercalated segment instability with an increased scapholunate angle and increased scapholunate gap (>3 mm)

●● stage IV: as stage III with associated secondary OA ●● SLAC: represents the end-stage of scapholunate instability and is classified into 4 stages:

●● stage 1: isolated OA between the radial styloid and scaphoid ●● stage 2: progression to radioscaphoid OA ●● stage 3: mid-carpal OA at the capito-lunate joint (Fig. 3.43c), with proximal migration of the capitate

into the widened scapholunate gap and reduced carpal height ●● stage 4: radiolunate OA and eventually pan-carpal OA (Fig. 3.43d) ●● although scapholunate injury is the leading cause of SLAC, it may also result from Kienböck’s disease

or CPPD disease ●● MRI findings:

●● features of SLL tear (Fig. 3.41) ●● sagittal images: show abnormal alignment of the radius, lunate and capitate:

● dorsiflexion of the lunate and proximal displacement of the capitate (Fig. 3.44a) with volar rotation of the scaphoid (rotatory subluxation) (Fig. 3.44b)

● an abnormal measurement of the scapholunate (>70°: normal 30-60°) and capitolunate (>30°: normal 0-30°) angles

●● coronal images:118 normally, the most volar portion of the lunate is seen 2-3 slices posterior to the proximal pole of the scaphoid:

● in DISI: volar slide of the lunate on the radial articular surface results in the volar surface being identified before or at the same time as the distal pole of the scaphoid (Fig. 3.44c), an apparent enlargement of the lunate (Fig. 3.44c) and associated ulnar slide of the bone with increased scapholunate distance (Fig. 3.44d)

●● dorsal tilt of the lunate may be simulated on MRI mimicking the DISI configuration, depending upon wrist position119 (Figs 3.45a, b):

● in the neutral position: the mean capitolunate, scapholunate and radiolunate MR angles are approximately 14°, 7°, and 19° larger compared with measurements from lateral radiographs

● with 15° ulnar deviation: the mean capitolunate, scapholunate and radiolunate MR angles are approximately 32°, 17°, and 37° larger compared with measurements from lateral radiographs

● with 15° radial deviation: measurements between MR and radiographs are equivalent ●● cine-MRI: correlates well with cine-radiography for the detection of dynamic scapholunate joint

space widening secondary to SLD, with 85% sensitivity and 90% specificity for the detection of SLD in comparison with arthroscopy116

●● lunotriquetral dissociation (LTD): has a variable aetiology, being associated with the latter stages of perilunate instability, tears of the LTL and secondary stabilisers, or the latter stages (IID and IIE) of ulnocarpal impaction

●● clinically: it presents with ulnar-sided wrist pain and a motion-associated click ●● LTD: results in volar flexion and slight dorsal translation of the lunate, with associated mild volar shift of

the distal carpal row: ●● this produces the VISI pattern of instability, volar intercalated segment instability ●● volar flexion of the lunate results in reduction of the scapholunate angle

●● LTD may be staged in a similar way to SLD, eventually resulting in mid-carpal OA (stage IV) ●● MRI findings:

●● sagittal images: show volar tilt of the lunate and increased capitolunate angle (Fig. 3.46a) with abnormal measurement of the scapholunate angle (<30°: normal 30-60°) due to associated volar tilt of the scaphoid

●● on coronal images:118 the most volar portion of the lunate is seen much later than normally and when seen, the lunate appears smaller than normal:

● the articulation and alignment of the lunate and triquetrum is disrupted ● on dorsal coronal images through the wrist, the dorsally slid lunate appears larger than normal (Fig. 3.46b)

●● radiocarpal instability (RCI): results from failure of the volar and dorsal extrinsic carpal ligaments causing ulnar and volar translation of the proximal carpal row on the distal radius:

●● the commonest causes are rheumatoid arthritis (RA) and Madelung deformity, while traumatic RCI is rare ●● RCI may also be iatrogenic, following excessive resection of the radial styloid process or ulnar head

●● MRI findings: ●● on coronal images: there may be ulnar translation of the entire proximal carpal row, resulting in

a radioscaphoid diastasis of >2 mm and radiolunate contact of <50% (Fig. 3.47) ●● alternatively, in the presence of intact radial-side extrinsic ligaments, the scaphoid maintains a normal

position, while the lunate translates ulnarly, resulting in scapholunate diastasis: ● this latter pattern represents a combination of CIND and CID, being termed carpal instability

complex (CIC)

●● extension of the digits involves the action of both extrinsic and intrinsic extensor muscles ●● the extrinsic muscles: originate in the forearm/elbow and insert in the hand and include:

●● extensor digitorum communis (EDC), extensor indicis proprius (EIP – which is absent or hypoplastic in ~40% of individuals), and extensor digitorum quinti minimi (EDQM)

●● these primarily extend the metacarpophalangeal (MCP) joints, but also the proximal (PIP) and distal (DIP) interphalangeal joints

●● the intrinsic muscles: originate and insert in the hand and include the interossei and lumbricals, which extend the PIP and DIP joints and flex the MCP joints

●● the extensor mechanism: is divided anatomically into 10 zones as follows: ●● zone X: the muscle belly ●● zone IX: the intramuscular tendon ●● zone VIII: the distal forearm ●● zone VII: the wrist extensor compartments ●● zones VI-I: the dorsum of the hand to the DIP joint level (see later)

●● zones X-VIII: comprise a superficial group of 5 muscles (common extensors) and 4 deep muscles: ●● the common extensors: include extensor carpi radialis longus (ECRL) and brevis (ECRB), extensor

digitorum (ED), extensor digiti minimi (EDM) and extensor carpi ulnaris (ECU): ● they originate from the common extensor origin at the lateral epicondyle of the humerus ● ECRL: inserts into the dorsum of the base of the 2nd metacarpal ● ECRB: inserts into the dorsum of the base of the 3rd metacarpal

● ED: inserts into the dorsal surface of the fingers ● EDM: inserts into the little finger ● ECU: inserts into the dorsoulnar side of the base of the little finger metacarpal

●● the deep muscles: comprise from the radial to ulnar side, the abductor pollicis longus (APL), extensor pollicis brevis (EPB), extensor pollicis longus (EPL) and extensor indicis (EI):

● they originate in the mid-forearm and interosseous membrane and travel in an oblique direction to the radial side of the wrist

● APL: inserts into the radial side of the base of the 1st metacarpal ● EPB: inserts into the base of the thumb proximal phalanx ● EPL: inserts into the base of the thumb distal phalanx ● EI: inserts into the dorsal side of the index finger

●● the extrinsic muscles are optimally visualised on axial MR images (Fig. 3.48a) ●● zone VII: the tendons on the dorsum of the wrist are stabilised by the extensor retinaculum, which is formed

from the deep part of the antebrachial fascia and consists of 2 layers: ●● supratendinous: which gives rise to 6 vertical longitudinal septa that insert onto the radius producing

6 compartments containing the respective extensor tendons, which are lined by a synovial sheath (Fig. 3.48b):

● 1st compartment: the floor comprises the radial styloid and insertion of the brachioradialis and contains the APL and EPB tendons, which form the radial margin of the anatomical snuff box: – it may be divided into 2 tunnels by a septum in up to 40% of individuals, 1 containing each tendon

● 2nd compartment: contains the ECRL and ECRB tendons ● 3rd compartment: separated from the 2nd compartment by Lister’s tubercle and contains the EPL tendon ● 4th compartment: contains the ED and EI tendons ● 5th compartment: located above the DRUJ and contains the EDM tendon ● 6th compartment: located along the dorsal aspect of the distal ulna and contains the ECU tendon

●● infratendinous: limited to the most ulnar side of the wrist ●● 2 tendon intersections are described:

●● proximal: at the distal third of the forearm (zone VIII), where the APL and EPB tendons cross the ECRL and ECRB tendons proximal to the extensor retinaculum (Figs 3.49a-c)

●● distal: at the carpus (zone VII), distal to the 3rd compartment, where the EPL tendon crosses the ECRB and ECRL tendons (Figs 3.49d, e) to form the ulnar margin of the anatomical snuff box

●● on MRI, mild increased SI can be seen: ●● within the EPL ( just distal to Lister’s tubercle) and ECU tendons due to magic angle effect (Fig. 3.50a) ●● within the ED tendons due to a small physiological amount of fluid within the tendon sheath (Fig. 3.50b) ●● due to striations within APL resulting from the presence of multiple tendon slips (Fig. 3.50c), which may

simulate longitudinal tears52

●● 1st extensor compartment: de Quervain’s disease is classically thought to represent tendinosis and stenosing tenosynovitis of the APL and EPB tendons, but may instead represent a stenosing tendinosis:125 ●● clinically: it occurs most commonly in middle-aged females, being bilateral in 30% and presenting with

pain and swelling at or just proximal to the radial styloid: ● it is predisposed to by anatomical variation of the 1st compartment, when 2 tunnels are present

●● aetiology: the condition is most commonly idiopathic, may be associated with underlying systemic diseases such as hypothyroidism, RA and gout, or may follow acute or repetitive trauma:

● ‘baby wrist’: occurs in nursing mothers ~8 months post-partum126

● ‘texting thumb’: repetitive injury from prolific mobile phone texting or video game controller use, manifesting as thumb/radial wrist pain related to tendinosis or tenosynovitis of the 1st or sometimes 3rd extensor compartments127

●● MRI findings: ● thickening of APL and EPB tendons, synovial effusion and surrounding soft-tissue oedema

(Figs 3.51a, b) ● diffuse thickening of the 1st extensor retinaculum is described48,128 ● increased tendon SI alone is an unreliable sign

●● 2nd compartment: intersection syndrome represents an inflammatory process (peritendinitis) of the ECRL and ECRB tendons:129 ●● clinically: characterised by pain and swelling 4-8 cm proximal to Lister’s tubercle ●● aetiology: most likely chronic overuse and friction at the proximal extensor intersection, and may also

result from stenosis of the tendon sheath ●● distal intersection syndrome: represents peritendinitis and tenosynovitis at the distal extensor intersection

and is much less common than proximal intersection syndrome130 ●● MRI findings:

● fluid surrounding the 1st and 2nd compartment tendon sheaths at the site of intersection in the distal forearm (Figs 3.51c, d): – soft-tissue oedema may be seen superficial to the intersection as well as in the intervening fat plane

between the two compartments

● distal intersection syndrome: results in peritendinous increased SI and tenosynovitis involving the 2nd and 3rd extensor compartment tendons (Fig. 3.51e)

●● 3rd compartment: EPL tenosynovitis and rupture are usually related to chronic friction against Lister’s tubercle, associated with degenerative or post-traumatic spurring: ●● it is also associated with RA and systemic lupus erythematosus (SLE), can occur 3 weeks to 3 months following

distal radial fracture, or may be secondary to an accessory EPL muscle within the 3rd extensor compartment ●● MRI findings:

● thickening of the EPL tendon and tenosynovial effusion ● chronic cases lead on to stenosing tenosynovitis with resultant scar tissue around the tendon ● acute tendon rupture: a fluid filled gap between the tendon ends ● chronic tear: scar tissue may fill the gap, obscuring the torn ends

●● 4th and 5th compartments: ED, EI and EDM tendon ruptures, which are divided into closed injuries and lacerations and are classified anatomically by a zonal system (see above): ●● injuries at the wrist and proximal forearm (zones VII and VIII) are typically lacerations, which may be

associated with significant proximal tendon retraction ●● 6th compartment: ECU tenosynovitis represents the second commonest site of wrist extensor tendon

inflammation after de Quervain’s disease: ●● aetiology: usually due to ECU tendon instability:

● ulnar subluxation: due to disruption of the ulnar aspect of the ECU tunnel allowing ulnar subluxation during wrist supination and volar flexion: – negative ulnar variance may be associated with ECU subluxation and ECU tendon pathology131 – seen in sports with repetitive wrist movements such as racquet sports requiring a snap of the wrist61

● dislocation: may result from recurrent instability, follow distal radial fracture with disruption of the extensor retinaculum, or be associated with DRUJ subluxation: – it is frequently seen in rheumatoid arthritis132

● central increased SI within an otherwise normal ECU tendon at the level of the DRUJ is a frequent finding of no clinical relevance, due to the formation of the tendon from the 2 muscle bellies of ECU (Fig. 3.52a)52

● abnormal tendon morphology (Fig. 3.52b) ● thickening of the tendon sheath, tenosynovial effusion and peritendinous oedema (Fig. 3.52c) ● chronic stenosing tenosynovitis: manifests as peritendinous low SI due to scarring (Fig. 3.52d) as well

as septation, loculation and synovial proliferation within the tendon sheath ● partial tears: manifest as intrasubstance longitudinal splits resulting in increased SI within the tendon ● instability of the tendon: can be assessed on axial images obtained in supination and pronation

(Figs 3.52e, f ) ● volar dislocation: is identified on axial images where the tendon is located over the medial aspect of

distal ulna (Fig. 3.52g)

●● the flexor muscles: of the wrist and hand originate from the medial epicondyle of the humerus (common flexor origin)

●● the flexor tendons: at wrist level may be classified into 2 groups, those within the carpal tunnel and deep to the flexor retinaculum (Figs 3.53a-c), and those outside the carpal tunnel (Figs 3.54a-d)

●● those within the carpal tunnel are surrounded by a common sheath and include: ●● flexor digitorum superficialis (FDS): which insert into middle phalanx ●● flexor digitorum profundus (FDP): which insert into the distal phalanx ●● flexor pollicis longus (FPL): which inserts into the base of the thumb distal phalanx ●● on low TE MRI sequences, increased SI may be seen within the FPL tendon in the distal carpal tunnel

and palm due to the magic angle effect (Fig. 3.53d)

●● those outside the carpal tunnel include: ●● flexor carpi radialis (FCR): which travels in a fibro-osseous tunnel formed by a reflection of the flexor

retinaculum just proximal to the trapezium and inserts into the trapezial tuberosity and bases of the 2nd and 3rd metacarpals (Figs 3.54c, d)

●● flexor carpi ulnaris (FCU): which together with the pisiform, forms the lateral boundary of Guyon’s canal and inserts into the palmar surface of the pisiform (Figs 3.27c and 3.54b), hamate and base of the 5th metacarpal

●● palmaris longus (PL): which does not have a synovial sheath but has a paratenon and inserts into the flexor retinaculum and palmar aponeurosis:

● the tendon is absent in ~25% of individuals ●● radial and ulnar bursae:134 are synovium-lined structures located on the volar side of the wrist, the radial

being associated with the FPL tendon and the ulnar with the FDS of the little finger (Fig. 3.54e): ●● the ulnar bursa: is composed of 3 invaginations that extend around the flexor tendons at the level of

the carpal tunnel, a superficial extension between the transverse carpal ligament and the FDS tendons,

a middle extension between the superficial and profundus flexor tendons and a deep layer lying deep to the flexor profundus tendons

●● the bursae commonly communicate with their adjacent tendons and an intermediate bursa may allow communication between the radial and ulnar bursae

●● tenosynovitis of the digital flexors: ●● traumatic: due to an acute hyperextension injury or chronic repetitive trauma ●● infective: TB, mostly atypical organisms, which may result in rice bodies135 (Fig. 3.55a) ●● systemic inflammatory disorders: RA, psoriatic arthropathy, SLE, gout ●● MRI findings:

● thickening of the tendon sheath with effusion (Figs 3.55b, c) and peritendinous oedema ● bursitis within the carpal tunnel is an associated feature of RA

●● tenosynovitis of FCR: which may be due to direct injury, chronic repetitive trauma, or may be idiopathic ●● FCR tendinopathy/tears:

●● repetitive trauma: as seen in racquet sports and golf results in shear stresses across the tendon which lead to a cascade of tenosynovitis, tendinosis and eventually tear34

● tendon sheath thickening (Fig. 3.55d), hyperintensity of the tendon on T2W images and inflammatory changes in the tri-scaphe joint

●● tenosynovitis of FCU:80 causes include: ●● chronic repetitive trauma: commonly seen in racket sports and golfers ●● calcific tendonitis: which may occur close to the pisiform insertion of FCU and is associated with

pisotriquetral OA ●● clinically: patients present with pain over the FCU or pisiform with painful ulnar flexion against

resistance, and possibly ulnar nerve symptoms ●● tenosynovitis of the 5th flexor tendon:80

●● digital flexor tendon rupture: closed ruptures are uncommon compared to lacerations, with predisposing factors to closed rupture including: ●● RA, OA, scaphoid non-union, Kienböck’s disease, DM,138 hook of hamate fractures, non-united distal

radial fractures and carpal dislocations ●● acute closed ruptures may occur following sudden hyperextension injuries

●● flexor tendon rupture: is classified according to the anatomical zone, with carpal tunnel level (zone IV) ruptures usually being secondary to RA

●● FPL tendon rupture: may occur secondary to chronic attrition against the scaphoid in RA or following volar carpal subluxation: ●● clinically: it results in loss of active thumb flexion at the interphalangeal joint and may produce carpal

tunnel syndrome due to tendon retraction into the tunnel ●● FCR tendon rupture: may be acute or chronic:

●● acute: following a fall onto the outstretched hand resulting in avulsion from its insertion ●● chronic: partial tears due to friction against bony spicules from the scaphotrapezium-trapezoid joint

●● accessory AbDM muscle: is reported with a prevalence of 24%, with sites of origin including the palmar carpal ligament, the palmaris longus tendon and the antebrachial fascia of the forearm

●● it usually inserts together with AbDM on the medial aspect of the base of the 5th MC ●● the muscle is usually asymptomatic, but if it becomes hypertrophied it may cause compressive neuropathy of

the ulnar nerve within Guyon’s canal ●● MRI findings:

●● a fusiform mass with signal characteristics of muscle located anterolateral to pisiform at the level of origin of the AbDM muscle, and lying anterior to Guyon’s canal

●● EDB manus muscle: is a dorsal accessory muscle with a reported prevalence of 1-3%, which typically originates from the distal radius and dorsal radiocarpal ligament and is located in the 4th extensor compartment

●● it inserts into the index finger, or less commonly into the middle finger ●● it is not commonly symptomatic but may result in pain with heavy activity and extremes of wrist extension ●● MRI findings:

●● an accessory muscle located medial to the extensor tendon(s) of the index finger at or just distal to the carpus

●● the lumbricals: may have a proximal origin from the FDP tendons within the carpal tunnel, with a reported prevalence of 22% and may cause carpal tunnel syndrome

●● MRI findings: ●● muscles within the carpal tunnel associated with the FDP tendons, but only evident with the wrist

scanned when the fingers are extended

●● PL muscle: may be absent in ~20% of individuals ●● the muscle may be fleshy throughout its length (non-tendinous), digastric, or may be bifid for part of its

course ●● the PL inversus variant: is described when the muscle is tendinous proximally and fleshy distally:

●● clinically: it may present with median or ulnar nerve compression or as a palmar soft-tissue mass ●● MRI findings:

●● a mid-line muscle mass identified superficial to the flexor retinaculum at the wrist level ●● PL inversus, non-tendinous and digastric types can only be diagnosed with more proximal imaging of

the forearm

●● digastric FDS: is an anomalous muscle belly of the FDS muscle to the index finger, which presents as a mass at the base of the index finger within the tendon of the FDS

●● MRI findings: ●● a muscle within the index finger FDS tendon at the level of, or just proximal to the metacarpal

●● just proximal to the wrist, the median nerve runs between the FDS and FCR muscles, then passes through the carpal tunnel (CT) with the flexor tendons of the fingers and thumb

●● within the carpal tunnel, the nerve lies superficial and lateral to the FDS tendons ●● the median nerve is optimally visualised on axial images, appearing of intermediate SI ●● the nerve should be assessed at 4 levels:

●● the DRUJ: where it appears round/oval in shape and lies deep to the PL tendon, medial and superficial to the FCR and FPL muscles, and lateral/superficial to the FDS (Fig. 3.56a)

●● the proximal CT: at the level of the pisiform and scaphoid bones, the nerve is slightly flattened and lies deep to the flexor retinaculum and superficial to the flexor tendons (Fig. 3.56b)

●● the distal carpal tunnel: at the level of the hook of hamate and trapezium, the nerve appears flattened (Fig. 3.56c)

●● the metacarpal bases (Fig. 3.56d): where the nerve divides into digital branches, which run superficial to the flexor tendons in the palm (Fig. 3.56e)

●● anatomical variants of the nerve in the carpal tunnel may be seen (Figs 3.56f, g) ●● The CT represents a fibro-osseous channel measuring ~6 cm in length with the following boundaries

(Figs 3.57a, b): ●● lateral: the tubercles of the scaphoid and trapezium ●● medial: the pisiform and hook of hamate ●● palmar boundary: the flexor retinaculum (transverse carpal ligament), a thickening of the deep

fascia running between the hook of hamate and pisiform to the tubercles of the scaphoid and trapezium

●● roof: formed by the carpal bones

●● anatomical variants: within the CT include persistence of the median artery (1-23%), a bifid median nerve144 (bifurcation occurs proximal to the carpal tunnel in ~6% and within the carpal tunnel in up to 18%), less commonly a trifurcated nerve and also various anomalous muscles: ●● reversed PL, palmaris profundus, accessory FDS and anomalous origins of the thenar and lumbrical

muscles ●● the median nerve supplies: the thenar muscles (Figs 3.58a, b):

●● abductor pollicis brevis (AbPB): which originates from the scaphoid, trapezium and flexor retinaculum and inserts into the lateral aspect of the base of the thumb proximal phalanx, together with flexor pollicis brevis (FPB)

●● opponens pollicis: which originates from the flexor retinaculum and inserts into the length of the lateral border of the thumb MC

●● FPB: which originates from the flexor retinaculum and inserts into the lateral aspect of the base of the thumb proximal phalanx, together with AbPB

●● the 1st and 2nd lumbricals ●● the terminal sensory branches: supply the palmar surface of the lateral 3½ fingers ●● the palmar cutaneous branch: arises proximal to the wrist and travels with the FCR tendon, superficial to

the flexor retinaculum, providing sensory innervation to the thenar eminence and proximal radial aspect of the palm

●● CTS: is the commonest compressive neuropathy of the upper limb (reported prevalence of 50-150/100,000)

●● clinically: it presents in the 40-60 year age range with pain and paraesthesia in the median nerve distribution typically affecting the dominant hand, and is more common in women (3:1)

●● aetiology: dynamic compression, mechanical compression by mass lesions, inflammatory conditions (non-specific flexor tenosynovitis, RA, gout), intrinsic nerve lesions, secondary to systemic conditions (DM, pregnancy, hypothyroidism), post-traumatic and musculotendinous anatomical variants: ●● an anatomical variant consisting of proximal division of the median nerve at the inlet of the CT is found

in 10-15% of patients with CTS ●● most cases are diagnosed clinically and with nerve conduction studies, while MRI may show extrinsic causes

of median nerve compression ●● MRI findings:

●● abnormalities of the median nerve: morphological changes including increased girth proximal to the CT, flattening of the nerve within the CT and increase T2W SI of the nerve146 (Fig. 3.59a):

● nerve enlargement assessed by comparing the cross-sectional area (CSA) of the nerve at the DRUJ level with that at the level of pisiform: – in CTS, the pisiform:DRUJ CSA ratio is 1.6 to 3.5

● flattening of the nerve within the CT assessed by the ‘flattening ratio’ (FR is the ratio of major to minor axis of the nerve) at the hook of hamate level (Fig. 3.59b) compared with DRUJ level (Fig. 3.59c): – in normal subjects the FR at the DRUJ is 2.5 and at the hook of hamate is 2.9, while in CTS the FR

at the DRUJ is 1.8 and at the hook of hamate is 3.8 ●● bowing of the flexor retinaculum: is secondary to increased pressure or volume within the CT, being

optimally evaluated at the level of the hook of hamate, where the retinaculum should be either straight (Fig. 3.59b) or slightly convex (Fig. 3.59d):

● bowing is assessed by dividing the distance of palmar displacement of the flexor retinaculum by the distance between the hook of hamate and tubercle of the trapezium (Fig. 3.59e)

● the normal bowing ratio is 0-0.15 (mean: 0.05), while in CTS the bowing ratio is 0.14-0.26 (mean: 0.18), being possibly one of the most specific signs of CTS

●● causes of median nerve compression include: nerve sheath tumours, fibrolipomatous hamartoma, ganglion cyst, fracture, OA and flexor tenosynovitis147 (Figs 3.55a-c)

●● occasionally, muscle oedema and atrophy may be seen ●● contrast-enhanced MRI: is useful in recurrent CTS following open surgical release to assess the

retinaculum, morphology of the median nerve and presence of fibrosis or tenosynovitis: ● reported sensitivity, specificity and positive predictive value for post-operative fibrosis of 60%, 83% and

92% respectively148

●● fibrolipomatous hamartoma: is now termed lipomatosis of nerve (LON) and most commonly involves the median nerve

●● pathologically: it consists of increased fatty tissue interspersed between thickened nerve bundles, with endoneural and perineural fibrosis

●● clinically: LON presents as swelling with/without symptoms of neural compression, with 27-66% of individuals having macrodactyly of the involved region, which if occurring at birth is termed macrodystrophia lipomatosa

●● MRI findings: ●● serpiginous low SI structures representing thickened nerve fascicles (Figs 3.60a, b) ●● evenly distributed fat between the nerve fascicles, appearing hyperintense on T1W (Figs 3.60a, b) and

hypointense on STIR (Figs 3.60c, d) ●● macrodystrophia lipomatosa: features of lipomatosis of the nerve and enlargement of the fingers/thumb

(Fig. 3.60e)

●● the ulnar nerve: together with the ulnar artery runs within Guyon’s canal (the ulnar tunnel) ●● Guyon’s canal: is located superficial and to the ulnar side of the flexor retinaculum, although its location is

dependent upon wrist position: ●● with the hand in a neutral position, the ulnar nerve usually lies medial to the hook of hamate (hamulus) ●● however, its position may vary from a point 7 mm ulnar to the hamulus, to a point 2 mm radial to

the hamulus ●● also, flexion and extension of the wrist induce ulnar and radial displacement of the nerve respectively

●● the canal is approximately 1.5 cm long and has the following boundaries: ●● anterior: the superficial transverse (volar) carpal ligament (Fig. 3.61a) ●● posterior: the deep transverse carpal ligament (flexor retinaculum) (Fig. 3.61b) ●● medial: the pisiform bone and pisohamate ligament (Fig. 3.61a) ●● posterolateral and distal: the hook of hamate (Fig. 3.61c)

●● the canal is divided longitudinally into 3 zones, related to the bifurcation of the ulnar nerve: ●● zone 1: just prior to bifurcation of the nerve, the area being triangular with a mean width of 11 mm and

mean depth of 7 mm ●● zone 2: contains the deep motor branch at the pisohamate hiatus (between the pisiform and hamate

bones), an area that measures ~13 mm by ~4 mm ●● zone 3: lies distally and contains the sensory branch only

●● proximal to Guyon’s canal, the nerve provides sensory innervation to the dorsal ulnar head and hypothenar eminence

●● within Guyon’s canal, the nerve divides into superficial sensory and deep motor branches (in 77% of cases)

●● the superficial branch supplies: ●● the palmaris brevis muscle, a thin subcutaneous muscle that arises from the flexor retinaculum and palmar

aponeurosis and inserts into the skin on the ulnar side of the hand ●● sensation to the little finger and ulnar half of the ring finger

●● the deep motor branch: which curves laterally around the hook of hamate, passes under a fibrotendinous arch (the pisohamate hiatus) (Figs 3.61d, e) to innervate the hypothenar muscles, the adductor pollicis, the 3rd and 4th lumbricals and all of the interossei

●● less commonly, the nerve bifurcates into radial and ulnar trunks, or trifurcates ●● the hypothenar muscles include:

●● AbDM: which usually has 2 bellies, originating from the pisiform, FCU tendon and pisometacarpal and pisohamate ligaments, and inserting into the ulnar side of the base of the 5th proximal phalanx and the adjacent extensor mechanism (Figs 3.62a-c)

●● flexor digiti minimi brevis (FDMB): originates from the hamulus, the adjacent flexor retinaculum and the radial part of pisiform, and inserts with AbDM (Figs 3.62a, c)

●● opponens digiti minimi (OpDM): has 2 layers, superficial (originating from the hamulus and inserting into the ulnar side of the distal 5th MC shaft), and deep (originating from the ulnar aspect of the flexor retinaculum and inserting into the ulnar side of the proximal 5th MC shaft) (Fig. 3.62c)

●● adductor pollicis (AdP): has 2 heads, the oblique and transverse: ●● the oblique head: originates from the volar surfaces of the 2nd and 3rd MC bases and adjacent carpal

bones ●● the transverse head: originates from the volar surface of the 3rd MC shaft (Fig. 3.62d) ●● both insert into the medial side of the base of the thumb proximal phalanx, together with the 1st palmar

interosseous muscle (Fig. 3.62d) ●● muscle variants: may be present in Guyon’s canal in 22-35% of individuals:

●● most commonly, accessory abductor digiti minimi (AbDM) muscles (see above) ●● also recognised are accessory palmaris muscles, anomalous flexor digiti minimi muscles and duplicate

tendons of FCU accompanied by splitting of the ulnar nerve ●● bilateral muscle variants are seen in ~50% of cases

●● ulnar tunnel syndrome: represents a compressive neuropathy of the ulnar nerve within Guyon’s canal and commonly affects sports such as cycling (handlebar palsy), martial arts and racquet sports: ●● it may also affect workers using vibrating tools or may be due to mass lesions in the ulnar tunnel ●● other causes include fracture of the hook of hamate, pisotriquetral OA, an os hamuli proprium (bipartite

hamulus), dislocation of the pisiform and systemic conditions as for CTS ●● clinically: presentation is dependent upon the site of compression, with 3 different zones described within

the canal: ●● zone 1: compression just proximal to or within the canal prior to bifurcation of the nerve, which results in

combined motor and sensory deficit

●● zone 2: compression of the deep motor branch at the pisohamate hiatus, which results in motor weakness (most common site)

●● zone 3: compression of the sensory branch only at the distal end of the canal (least common site), which results in sensory deficit affecting the palmar aspect of the hand only

●● MRI findings: ●● the cause of compression:

● anomalous muscles, which account for ~3% of cases, most commonly an anomalous AbDM ● mass lesions and ganglia (Fig. 3.63a)

●● denervation oedema and atrophy of the affected muscles (Figs 3.63b, c)

●● the 1st carpometacarpal joint (CMCJ): is composed of the articulation between the distal surface of the trapezium and the base of the first metacarpal

●● the joint is stabilised by a combination of ligaments, surrounded by tendons and the thenar muscles ●● 4 main ligaments contribute to 1st CMCJ stability:

●● the anterior oblique ligament (AOL): a short thick band running from the palmar tubercle of the trapezium to the base of the thumb metacarpal (Fig. 3.64a), having a superficial and deep (intra-articular) component

●● the dorsal radial ligament (DRL): arises from the dorsoradial aspect of the trapezium and inserts onto the adjacent thumb metacarpal base (Fig. 3.64b), being reinforced by the APL tendon

●● the posterior oblique ligament (POL): runs from the dorsal-ulnar tubercle of the trapezium to the ulnar tubercle of the thumb metacarpal base

●● the intermetacarpal ligament (IMCL): runs from the ulnar aspect of the thumb metacarpal to the radial aspect of the base of the index finger metacarpal (Fig. 3.64c), and typically has a striated appearance

●● the UCL: is located at the ulnar aspect of the AOL, originating from the flexor retinaculum and inserting onto the ulnopalmar tubercle of the 1st metacarpal (Fig. 3.64d)

●● acute injury: usually occurs following an axial load with flexion of the thumb metacarpal resulting in dorsal dislocation, due to a direct blow, or associated with a fracture to the base of the metacarpal

●● clinically: it presents with pain and focal tenderness deep to the thenar eminence ●● MRI findings:

●● most commonly injury to the superficial AOL (~90% of cases), typically at or adjacent to the distal insertion (Fig. 3.65a):

● tears may be partial or complete, with/without stripping of the periosteum from the thumb metacarpal base

●● DRL injury: occurs in ~80% of cases, usually from the proximal aspect (Fig. 3.65b) ●● isolated dislocation, which is uncommon results in rupture of the DRL and POL ●● additional features: bone marrow oedema on either side of the joint and soft-tissue oedema/haematoma

(Fig. 3.65c) ●● chronic ligament injury:

● manifests as laxity and thickening of the involved ligaments (Fig. 3.65d) and may be associated with OA of the joint, manifest as joint space loss, marginal osteophytes, subchondral sclerosis and cyst formation

● AOL and IMCL rupture is frequently seen in the context of established OA and imaging the thumb in two planes during thumb extension and abduction is reported to improve ligament visualisation157

● subluxation of the thumb metacarpal on the trapezium (Fig. 3.65e) is a common finding in asymptomatic individuals156

●● the 2nd-5th carpometacarpal (CMC) articulations: are formed between the distal surfaces of the trapezoid, capitate and hamate with the adjacent bases of the index, middle, ring and little finger metacarpals: ●● trapezoid with the index finger MC, capitate with middle finger MC and hamate with the ring and little

finger MCs (Fig. 3.66a) ●● the CMCJs: are supported by an assortment of ligaments and tendons

●● 6 carpometacarpal (CMC) ligaments: ●● the dorsal common CMC (CCMC) ligaments: which extend from the dorsal aspects of the distal row

carpal bones to the dorsal aspects of the bases of the index to little finger MCs, thick bands that are optimally demonstrated on sagittal MR images (Fig. 3.66b)

●● the palmar (volar) CCMC ligaments: which extend from the palmar aspects of the distal row carpal bones to the palmar aspects of the bases of the index to little finger MCs (Fig. 3.66b), not routinely seen on MRI since they are very thin structures

●● the pisometacarpal ligament (PML): which extends from the volar aspect of the pisiform to the bases of the volar aspects of the ring and little finger MCs, routinely demonstrated on sagittal (Fig. 3.27e) and axial (Fig. 3.66c) images running on the ulnar side of the hook of hamate

●● RCL: which extends from the dorsoradial aspect of the trapezoid to the dorsoradial aspect of the index finger MC

●● the capito-third ligament (CTL): which extends from the ulnar side of the capitate to the ulnar side of the middle finger MC (Fig. 3.66d)

●● the UCL: extending from the dorsoulnar aspect of the hamate to the dorsoulnar aspect of the little finger MC (Fig. 3.66e)

● the RCL, CTL and UCL are consistently visualised on coronal MR images

●● 3 intermetacarpal ligaments (IMCL): ●● the dorsal IMCL: a thin structure extending between the dorsal aspect of the index to little finger

metacarpals, commonly visualised on axial images (Fig. 3.66f) ●● the palmar IMCL: a thin structure extending between the palmar aspect of the index to little finger

metacarpals, commonly visualised on axial images (Fig. 3.66f) ●● the interosseous IMCL: comprises anterior and posterior bands linking the bases of the MCs, commonly

visualised on axial images (Fig. 3.66f) ●● tendons: comprise 4 insertions into the metacarpal bases:

●● the ECRL (Fig. 3.67a) and flexor carpi radialis longus (FCRL) (Fig. 3.67b) tendons into the dorsal and palmar base of the index finger MC respectively

●● ECRB into the base of the middle finger MC (Fig. 3.67c) ●● ECU into the base of the little finger MC (Fig. 3.67d)

●● injury to the CMC and IMC joints: is usually due to large torsional forces applied to the hand ●● CMC joint dislocations: most commonly result in dorsal displacement of the MCs and most commonly

involve the little finger followed by the index, middle and ring fingers ●● they may be subtle radiographically ●● MRI findings of ligament injuries are not yet described in the literature

●● the MCP joints: are uni-condylar joints that allow a degree of rotation and radial/ulnar deviation, as well as flexion/extension

●● the joint capsule: is attached proximally to an elevated crest surrounding the head of the MC and distally to a ridge separating the concave articular surface of the proximal phalanx (PP) from the shaft of the PP: ●● it is optimally demonstrated on sagittal MR images in the presence of an effusion, or on direct MR

arthrography ●● the collateral ligaments: are situated on the radial (RCL) and ulnar (UCL) sides of each MCP joint and blend

with and reinforce the capsule: ●● they comprise 2 bands, the main (proper) collateral and the accessory collateral ligaments ●● the main collateral ligaments: arise in depressions on the radial and ulnar sides of the MC head and insert

on the base of the PP, being optimally demonstrated on axial MR images with the joint flexed, or on coronal images with the joint extended (Fig. 3.68a)

●● the accessory collateral ligaments: arise in a slightly more palmar location than the main collateral ligaments and insert into the base of the PP, being optimally visualised on axial images with the joint extended

●● the palmar (volar) plate: which represents a dense fibrous structure lying on the palmar surface of the joint (Fig. 3.68b) between the accessory collateral ligaments, to which it is fused and also being attached firmly to the base of the proximal phalanx: ●● a small joint recess is present between the distal palmar plate and its phalangeal attachment, being

optimally visualised on sagittal images (Fig. 3.68c) ●● the deep transverse metacarpal (interglenoid) ligament (DTML): consists of thin fibrous bands that connect

the adjacent palmar plates: ●● the lumbrical muscles and the digital nerve and vessels are located on the palmar aspect of the DTML ●● the interosseous muscles and tendons are located on the dorsal aspect of the DTML ●● the DTML is optimally visualised on axial images with the joint extended (Fig. 3.68d)

●● the extensor hood: comprises the sagittal bands, the transverse fibres and the extensor muscles/tendons: ●● the sagittal bands: are thin bands that extend from the common extensor tendon to the junction of

the palmar plate and DTML ●● they run between the main collateral ligaments and the interosseous tendons and are demonstrated on

axial images (Fig. 3.68d) ●● the transverse fibres: form a triangular lamina distal to the sagittal bands and extend between the extensor

and interosseous tendons, being demonstrated on axial images with the joint extended ●● additional anatomical findings of the 1st MCP joint include:

●● a strong tendinous insertion of the AdP into the base of the proximal phalanx and volar-plate/sesamoid complex (Figs 3.68e, f )

●● some fibres of APL contribute to the adductor aponeurosis, which covers the UCL (Fig. 3.68g) ●● muscles and tendons:

●● the digital flexor tendons: comprise deep and superficial muscle tendons that extend across the joint (Fig. 3.68c):

● tendon sheath position in relation to the palmar plate is maintained by the A1 pulley, which itself is attached to the junction of the palmar plate and DTML, being demonstrated on axial images with the joint extended (Fig. 3.68b)

●● the 7 interosseous muscles and tendons: comprise 3 palmar and 4 dorsal: ● the palmar interossei: originate from the 2nd, 4th and 5th metacarpals and act to flex the MCPJ and

extend the interphalangeal (IP) joints ● the dorsal interossei: originate from the adjacent metacarpals, the 1st and 2nd lie on the radial sides

of the 2nd and 3rd MCs, the 3rd and 4th lie on the ulnar sides of the 3rd and 4th MCs, all act to abduct the fingers, flex the MCP joints and extend the IP joints

● the interossei lie dorsal to the DTML and insert into the proximal phalanx and extensor hood, being demonstrated on axial and coronal images with the joint extended (Figs 3.69a, b)

●● the 4 lumbrical muscles: originate from the deep flexor tendons in the mid-palmar region and lie palmar to the DTML, running on the radial side of the corresponding MCP joint to insert into the distal extensor mechanism:

● they are flexors of the MCP joints and extensors of the IP joints, and are demonstrated on axial images (Fig. 3.69a)

●● dislocation of the MCP joint: is an uncommon injury that results from forced hyperextension resulting in dorsal displacement, and may be classified as simple or complex: ●● simple injuries: the volar plate is not interposed within the joint and treatment is conservative ●● complex injuries: interposition of the volar plate may prevent reduction of the joint and treatment is

surgical ●● in the setting of chronic joint pain/disability:158 the commonest injury demonstrated is to the collateral

ligaments, usually on the radial side and optimally visualised on contrast-enhanced axial T1W images with the fingers flexed: ●● MRI shows ligament discontinuity or detachment, ligament thickening with increased T2W SI,

or extravasation of joint fluid into the adjacent soft tissues ●● associated lesions included injury to the extensor hood, interosseous tendon, volar plate and rarely an

osteochondral lesion ●● ~60% of MCP joint collateral ligament injuries involve the thumb

●● gamekeeper’s thumb:161,162 traditionally refers to a chronic injury of the 1st MCP joint UCL, in contrast to acute UCL injury seen frequently in skiing accidents (termed ‘skier’s thumb’):163 ●● it results from violent hyperabduction of the thumb MCP joint, which results in partial or complete

rupture of the UCL, usually from its distal attachment, with/without associated bony avulsion ●● ligament tears are common, reported to represent up to 86% of all injuries to the base of the thumb163 ●● following complete UCL rupture, the UCL may remain deep to the adductor aponeurosis and retraction

may be minimal ●● alternatively, severe retraction of the UCL may result in interposition of the adductor aponeurosis and

superficial location of the UCL (Stener lesion), which requires surgical management ●● MRI findings:

●● MCP dislocation: MRI findings include ligament discontinuity/detachment, ligament thickening with increased T2W SI, or extravasation of joint fluid into the adjacent soft tissues:

● MR also demonstrates the integrity and location of the volar plate ●● a collateral ligament tear may be seen with lateral/medial deviation injury and MCP flexion

(Figs 3.70a-c) ●● gamekeeper’s/skier’s thumb:

● an undisplaced UCL tear appears as a discontinuity and thickening of the otherwise normally located ligament (Fig. 3.70d)

● with a displaced UCL tear, the UCL is retracted to the proximal margin of the adductor aponeurosis and appears as a rounded/stump-like low SI mass, which has been termed ‘yo-yo on a string’: – the string representing the adductor aponeurosis and the yo-yo representing the rounded and

proximally retracted UCL

– fluid is seen around the adductor aponeurosis (Fig. 3.70e) and there may be soft-tissue oedema or haemorrhage, joint effusion and bone bruising

● MR arthrography is more sensitive and accurate in the demonstration of both acute and chronic UCL injuries162

●● disorders of the intrinsic muscles of the hands: may be due to primary muscle disease, or more commonly secondary to nerve injury

●● MRI may demonstrate the features of muscle injury, including: ●● denervation oedema or atrophy secondary to nerve injury, the pattern of muscle involvement indicating

the site of nerve damage (Figs 3.63b, c)

●● the proximal interphalangeal (PIP) joint: is a bi-condylar hinge joint stabilised by surrounding soft tissues, particularly the collateral ligaments and volar plate

●● dynamic stability: is maintained by the extensor mechanism, flexor tendons and retinacular ligaments

●● the collateral ligament complex (CLC): comprises the collateral ligament proper and the accessory collateral ligament: ●● the collateral ligament proper: arises at the dorsolateral aspect of the proximal phalangeal head and inserts

at the volar and lateral aspects of the base of the middle phalanx ●● the accessory collateral ligament: arises at the same site as the collateral ligament proper and inserts into

the volar plate ●● the CLC is optimally visualised on coronal images (Fig. 3.71a)

●● the volar plate: is a thick fibrocartilaginous structure that forms the palmar aspect of the PIP joint capsule, being attached to the proximal phalanx by 2 lateral bands called the ‘checkrein’ ligaments and extending distally to attach firmly to the volar aspect of the middle phalanx: ●● it prevents hyperextension of the PIP joint and is optimally visualised on sagittal images (Fig. 3.71b)

●● the extensor apparatus: provides dorsal stability to the PIP joint and consists of a central slip that inserts onto the dorsal tubercle of the middle phalanx, and medial and lateral slips that are connected by the retinacular ligaments (Figs 3.71b, c)

●● the PIP joint: is the most commonly injured joint in the hand, with injury resulting in either coronal or sagittal instability

●● coronal instability: occurs following either abduction or adduction forces to the extended joint, with 3 injury patterns described: ●● ligament sprain, partial ligament tear or complete ligament tear ●● complete ligament tears are usually associated with complete or partial avulsion of the volar plate from

the middle phalanx

●● MRI findings: ● discontinuity, detachment or thickening of the ligament with increased T2W SI, periarticular oedema

and swelling ●● sagittal instability: occurs following hyperextension or rotational axial compression of the joint:

●● hyperextension lesions are divided into 3 types: ● type 1: avulsion of the volar plate from the base of the middle phalanx, or less commonly

from its proximal attachment, resulting in hyperextension or pseudoboutonniere deformity respectively

● type 2: volar plate injury plus injury to the CLC resulting in dorsal subluxation of the middle phalanx

● type 3: fracture-dislocation of the volar base of the middle phalanx resulting in either a stable injury (<40% of the articular surface involved) or an unstable injury (>40% of the articular surface involved) with resulting dorsal subluxation, the latter requiring open reduction and internal fixation

●● compression-rotation injury: of the semi-flexed PIP results in volar subluxation of the middle phalanx with unilateral disruption of the collateral ligament and partial/complete disruption of the volar plate:

● there may be an associated lesion of the extensor apparatus ● if untreated, the injury may result in a chronic boutonniere deformity with PIP flexion and DIP

extension ●● MRI findings:

● depend upon the lesion grade ● oedema and swelling of the volar plate with detachment and soft-tissue oedema ● intra-articular fracture of the volar base of the middle phalanx and joint deformity

●● the extensor tendons: at the level of the MCP joints, are stabilised over the dorsum of the metacarpals by the extensor hood

●● distal to the MCP joints, the tendons of the extrinsic and intrinsic muscles fuse to form the dorsal apparatus, comprising the central slip and medial/lateral slips (bands) (Fig. 3.71c): ●● the central slip inserts on the base of the middle phalanx (Fig. 3.71b)

●● the fusion of fibres from the intrinsic tendons to the medial/lateral slips forms the conjoined tendons, which converge distally to form the terminal tendon which inserts into the distal phalanx

●● the extensor mechanism is optimally assessed on sagittal and axial MR images (Figs 3.72a, b)

●● extensor tendon injury: may be classified as open or closed ●● open injuries: are classified into 8 zones (zone 1 = distal interphalangeal joint (DIPJ): zone 8 = distal forearm):

●● odd zones: correspond to articular areas, thus injuries in these regions may be associated with articular disruption

●● laceration of the tendon in zone 1: results in a flexion deformity of the distal phalanx (open mallet deformity) ●● laceration of the central slip in zone 3: can result in boutonnière deformity (flexion of the PIP and

hyperextension of the DIP) ●● injury in zone 5: may result in rupture of the EDC tendon and the sagittal bands, resulting in tendon

subluxation/dislocation ●● MRI findings:

● partial-thickness tears: appear as areas of increased SI on T1W and T2W images in a portion of the tendon ● complete tears: appear as an area of complete tendon disruption, fraying of the tendon ends and

hyperintense fluid/haemorrhage within the gap ●● closed injuries: include mallet finger (also termed ‘baseball finger’), boutonnière deformity and subluxation/

dislocation of the extensor tendon: ●● mallet finger: is usually due to acute, forced hyperflexion of the extended DIPJ, typically with the

fingertip being struck by a baseball/basketball while the finger is held in rigid extension: ● associated with avulsion fracture of the dorsal base of distal phalanx or disruption of the terminal

extensor tendon without fracture ● clinically: manifests as a flexion deformity of the DIPJ and if left untreated, the injury may progress to

a ‘swan neck’ deformity (hyperextension of the PIP joint) ● surgery is usually indicated if there is a fracture of the base of the distal phalanx with a dorsal fragment

involving >30% of the articular surface, fragment separation by >3 mm, or palmar subluxation of the distal phalanx166

●● boutonnière deformity: occurs following forced flexion injury to the extended PIP joint, palmar dislocation of the middle phalanx, or a direct blow to the back of the hand resulting in avulsion of the central slip from its middle phalangeal base insertion:

● a similar appearance commonly occurs in inflammatory arthritis due to synovitis and capsular distension at the PIP joint resulting in chronic elongation and attrition of the central slip167

●● subluxation/dislocation of the extensor tendon: occurs secondary to rupture of the sagittal bands of the extensor hood, most commonly ulnar subluxation of the middle finger

●● MRI findings: ● tenosynovitis ● disruption and increased SI of the affected portion of the extensor mechanism (Figs 3.73a, b)

●● the digital flexor tendons: pass through the carpal tunnel before spreading out in the palm of the hand towards their respective fingers

●● each finger has 2 flexor tendons, FDS and FDP (Figs 3.74a, b) ●● the FDS tendon: splits at the distal metacarpal, passes around the FDP tendon and reunites deep to the FDP

tendon at the level of the PIP joint to insert into the mid-portion of the middle phalanx ●● the FDP tendon: inserts into the volar aspect of the distal phalanx (Fig. 3.74c) ●● from the metacarpal neck to the distal phalanx, each tendon runs along a fibro-osseous canal within

a synovial sheath ●● the floor of the canal is formed by the volar aspect of the respective bone and the volar plate at each

joint level

●● the fibrous portion of the canal is formed by 5 annular pulleys (A1-5) and 3 cruciform pulleys (C1-3) ●● the annular pulleys (Fig. 3.74d): represent focal transverse thickenings of the tendon sheath:

●● A1: spans the volar plate of the MCP joint to PP base (Fig. 3.68b) ●● A2: arises from the volar aspect of the PP base and extends to just proximal to the neck of the PP ●● A3: is located at the level of the PIP joint ●● A4: is located at the mid-portion of the middle phalanx (MP) ●● A5: is located at the level of the DIP

●● the cruciform pulleys: represent crossing fibres between the annular pulleys: ●● C1: is located between A2 and A3 ●● C2: is located between A3 and A4 ●● C3: is located between A4 and A5

●● the pulley system functions to stabilise the flexor tendons during finger flexion

●● flexor tendon injuries: may be classified as open or closed injuries, and injuries to the pulley system ●● open injuries: comprise lacerations most often involving the mid-substance of the tendon and are classified

into 5 zones: ●● zone 1: the distal insertion of FDP to the distal insertion of FDS ●● zone 2: the distal insertion of FDS to the distal palmar fold ●● zone 3: the proximal part of the A1 pulley to the distal part of the flexor retinaculum ●● zone 4: the carpal tunnel ●● zone 5: the forearm proximal to the flexor retinaculum ●● the thumb has 3 zones:

● T1: extends from the A2 pulley to the FPL tendon insertion ● T2: extends between the A1 and A2 pulleys ● T3: extends between the distal wrist crease and the A1 pulley

●● MRI findings: ● partial or complete tendon disruption ● complete disruptions may be associated with tendon retraction ● associated findings include: tenosynovitis, subluxation or dislocation of the tendon and pulley lesions

●● closed injuries: include avulsions of the FDP and FDS tendons and are classified into 4 types: ●● type 1: retraction of the tendon into the palm ●● type 2: retraction of the tendon to PIP joint ●● type 3: avulsion of a bony fragment, which is held in place by the A4 pulley ●● type 4: a type 3 lesion with additional avulsion of the FDP tendon from the bone fragment ●● the commonest injury is termed ‘Jersey finger’ and represents an avulsion of the FDS and FDP tendons

from their respective insertions: ● it is due to forced hyperextension of the DIP joint while the DIP joint is actively flexed and usually

involves the ring finger ●● isolated avulsion of the FDS tendon is rare and is usually associated with FDP rupture ●● MRI findings:

● tendon disruption without/with retraction (Fig. 3.75a) ● peritendinous oedema (Fig. 3.75b)

●● pulley injuries: are particularly associated with activities such as rock climbing: ●● the injury begins at the distal aspect of the A2 pulley, and complete rupture can extend to involve the A3

and A4 pulleys, and rarely the A1 pulley ●● MRI findings:

● displacement of the flexor tendon from the underlying phalanx (bow-stringing sign) shown on sagittal images obtained during forced flexion (Fig. 3.75c)

● axial images may show fluid/haemorrhage between the flexor tendon and underlying bone

●● proliferative periosteal processes: include florid reactive periostitis, bizarre parosteal osteochondromatous proliferation (BPOP), periostitis ossificans, turret exostosis and subungual exostosis

●● they represent a related group of disorders that may have as a common precursor a focus of subperiosteal haemorrhage, with the different lesions representing different stages of healing

●● florid reactive periostitis: is a rare benign lesion most commonly affecting the small bones of the hands and feet ●● it is also referred to as: parosteal fasciitis, panniculitis ossificans, benign fibro-osseous pseudotumour,

pseudomalignant osseous tumour of soft tissue, nodular fasciitis and pseudosarcomatous fibromatosis ●● clinically: it usually presents in the 2nd-3rd decades, with a history of trauma being present in 10-50% of cases ●● sites of involvement include the proximal phalanx, middle phalanx, metacarpal and distal phalanx in

decreasing order of frequency ●● MRI findings:171

● a soft-tissue paraosseous mass with a low SI rim and associated soft-tissue oedema (Figs 3.76a, b), possibly with associated adjacent bone marrow oedema (Fig. 3.76c)

●● BPOP: is also termed ‘Nora’s lesion’ and appears radiologically as a well-defined, calcified or ossified lesion arising from the cortex

●● ~55% of cases arise in the hand, usually involving the proximal or middle phalanx ●● clinically: it presents in the 3rd-4th decades as a painless, slowly enlarging swelling, usually without a history

of trauma ●● pathologically: BPOP is typically differentiated from an osteochondroma by the lack of continuity of the

lesion with the medulla of the underlying bone, although a few cases with cortico-medullary continuity have been reported173

●● most lesions are 0.5-3.0 cm in size

●● MRI findings: ●● a lobular mass arising on the surface of the bone, with SI characteristics depending upon the degree of

maturation and calcification/ossification of the lesion ●● an immature lesion may show intermediate T1W SI (Fig. 3.77a), increased T2W/STIR SI

(Figs 3.77b, c) and enhancement following contrast (Fig. 3.77d)

●● a heavily calcified BPOP typically has intermediate/low SI on all pulse sequences (Fig. 3.77e), whereas the presence of mature ossification results in central marrow SI (Fig. 3.77f)

●● marrow invasion is not seen, although cortical invasion, marrow and soft-tissue oedema may rarely be present

●● periostitis ossificans: is rare in the hand, being similar to myositis ossificans though occurring in a periosteal location

●● radiologically: it is characterised by the typical peripheral zoning pattern of soft-tissue mineralisation ●● MRI findings:

●● soft tissue and medullary oedema is seen (Figs 3.78a, b), together with periosteal reaction (Fig. 3.78c) ●● as the lesion progresses, the typical peripheral mineralisation may be demonstrated as a low SI ring

(Fig. 3.78d)

●● turret exostosis: is a rare complication of minor hand trauma that is thought to result from ossification of a subperiosteal haematoma, most commonly involving the middle or proximal phalanx

●● clinically: there is almost always a history of trauma, with progressive symptoms over the next few months ●● radiologically: as with other post-traumatic lesions, there is initially soft-tissue swelling followed by slowly

maturing juxta-cortical bone formation terminating in the development of a dome-shaped ossified lesion ●● MRI findings:

●● will depend upon the stage at which imaging is performed ●● the mature lesion appears as a well-defined bony mass protruding from the cortex of the phalanx (Fig. 3.79)

●● soft-tissue masses: of the wrist, hand and fingers may be either non-neoplastic, benign or malignant (least common) neoplasms

●● the MRI findings of common soft-tissue tumours are as described elsewhere (see Chapter 7; The Limbs)

●● Dupuytren’s contracture (palmar fibromatosis): represents a proliferation of fibrous tissue within the palmar aponeurosis of the hand, most commonly affecting the 4th ray

●● clinically: patients usually present in the 6th-7th decade with nodules in the distal palm crease that eventually progress to flexion contractures, with bilateral lesions in 40-60% ●● Caucasians, particularly those of northern European descent are predominantly affected, with patients of

African or Asian origin rarely affected ●● plantar fibromatosis, knuckle pad fibromatosis and Peyronie’s disease are more frequently seen in patients

with Dupuytren’s contracture

●● MRI findings: ●● hypointense fibrous nodules or cords arising from the palmar aponeurosis extending distally and

superficially parallel to the flexor tendons ●● the cords terminate in the superficial tissues at the level of the distal metacarpal ●● highly cellular lesions may be relatively hyperintense on T2W images (Figs 3.81a, b)

●● GCTTS: now referred to as tenosynovial giant cell tumours, localised type according to the World Health Organisation (WHO) classification 2013,177 represents the localised (nodular) form of extra-articular pigmented villonodular synovitis (PVNS) and is the second commonest soft-tissue mass of the wrist and hand after ganglion cyst: ●● conversely, 67% of all GCTTS occur in this region

●● clinically: it usually presents as a slowly growing, painless mass in adults in the 3rd-4th decades with a slight female predominance

●● pathologically: the lesion more commonly occurs on the volar aspect of the first 3 digits, although lateral and circumferential location is also reported, as is multifocal disease: ●● GCTTS arises from the synovium of the tendon sheath, small joints or bursae of the hand and is typically

a multi-lobular mass surrounded by a collagenous capsule ●● MRI findings:

●● GCTTS typically has intermediate T1W SI (Fig. 3.82a), variable T2W SI depending upon the degree of cellularity (Fig. 3.82b) and increased SI on PDW/STIR (Fig. 3.82c)

●● areas of low SI are commonly identified, being most prominent on T2W GRE images, and enhancement is seen following contrast

●● pressure erosion of the underlying bone is reported in 23% of cases (Fig. 3.82b), and the lesion may present radiologically as an intraosseous tumour,182 which may expand the bone in 11% of cases

●● the tumour is round or oval, being located eccentrically to the tendon, or encasing the tendon partially or completely (Figs 3.82a-c)

●● glomus tumours: represent small hamartomas of the neuromyoarterial apparatus of the glomus body, and account for ~5% of soft-tissue tumours of the hand

●● they are most commonly located at the finger tip, either in the pulp space or under the nail, although occasionally they may be intraosseous186

●● clinically: they most commonly present in the 4th-5th decades as exquisitely painful lesions, with symptoms affected by temperature changes: ●● disappearance of pain following application of a tourniquet proximally is diagnostic (the Hildreth sign)

●● MRI findings: ●● if the lesion is large enough, it may cause smooth pressure erosion of the adjacent bone (Fig. 3.83a) ●● these small tumours are typically of low/intermediate SI on T1W images and homogeneously

hyperintense on T2W/STIR (Figs 3.83a, b), showing uniform enhancement following contrast