The Elbow

The Ulnohumeral Joint ●● the ulnohumeral joint: consists of the articulation between the trochlea of the distal humerus and the greater

sigmoid notch of the ulna (Figs 2.3a, b) ●● the greater sigmoid (trochlear) notch: lies between the olecranon and coronoid processes of the proximal ulna

(Fig. 2.3c): ●● up to 98% of individuals have a transverse central bony ridge crossing the mid-portion of the trochlear

notch, dividing it into anterior and posterior portions ●● the trochlear ridge: lacks articular cartilage and measures approximately 2-3 mm wide and 3-5 mm in

height: ● it is identified in 81% of elbow MRI studies of normal volunteers (Fig. 2.3d) and should not be

mistaken for a central osteophyte or olecranon stress fracture ●● adjacent to the central trochlear ridge, sagittal MR images demonstrate a groove in the articular surface

of the ulna, the ‘trochlear groove’ (Figs 2.3e, f ), which should not be mistaken for a chondral defect ●● during elbow extension, the tip of the olecranon inserts into the olecranon fossa of the distal humerus

(Fig. 2.3g), while during elbow flexion the tip of the coronoid inserts into the coronoid fossa of the distal humerus (Fig. 2.3g)

The Radiocapitellar Joint ●● the radiocapitellar joint: is formed by the capitellum of the distal humerus and the radial head (Figs 2.4a, b) ●● during elbow flexion, the radial head inserts into the radial fossa of the distal humerus (Fig. 2.4b)

●● the anterior 180° of the capitellum is covered by articular cartilage with a bare area of the lateral epicondyle present posteriorly, their intersection forming the ‘pseudodefect’ of the capitellum (Figs 2.4c d): ●● a pseudodefect is observed in 85% of asymptomatic subjects with conventional elbow MRI13 ●● contrast medium may fill the pseudodefect at MR arthrography (Figs 2.4e, f ), and this should not be

mistaken for an osteochondral defect, which tends to occur anteriorly

The Proximal Radio-ulnar Joint ●● the proximal radio-ulnar joint (PRUJ): is formed by the articulation between the radial head and the lesser

sigmoid (semi-lunar) notch of the proximal ulna (Figs 2.5a, b) ●● approximately 240° of the outer circumference of the radial head is covered by hyaline cartilage, while the

anterolateral one-third is not covered ●● distal to the radial head are the radial neck and tuberosity (Fig. 2.5c)

The Humeral Epicondyles ●● the medial and lateral humeral epicondyles are extracapsular structures (Figs 2.6a, b) ●● the medial epicondyle: gives origin to the anterior and posterior bands of the UCL and the common flexor

tendon ●● the lateral epicondyle: gives origin to the lateral ligament complex and common extensor origin

●● Panner’s disease: represents an osteochondrosis of the humeral capitellum ●● pathologically: repeated valgus stress causes chronic compression of the lateral elbow, which is thought to

compromise the immature blood supply to the capitellar epiphysis: ●● the entire capitellar epiphysis is usually involved, which can be helpful in distinguishing this condition

from osteochondritis dissecans (see later) ●● clinically: it typically affects males aged 7-12 years during the period of active ossification of the capitellar

epiphysis: ●● it presents with pain, swelling and tenderness over the lateral elbow, and is a self-limiting process

●● MRI findings: ●● reduced T1W SI and increased T2W/STIR SI in the capitellum ●● irregularity of the capitellar articular surface with a low SI subchondral line consistent with avascular

necrosis (AVN) ●● joint effusion

●● osteochondritis dissecans (OCD): of the elbow most commonly involves the humeral capitellum (~92%): ●● rarely it occurs in the radial head (Fig. 2.7) ●● the trochlea is uncommonly affected by OCD (Figs 2.8a, b): usually involving the posterior inferior

aspect of the lateral trochlea, which corresponds to a watershed zone of diminished vascular supply18

●● pathologically: OCD is likely due to trauma associated with sporting activities resulting in repetitive overuse of the elbow, therefore typically involving the dominant arms of young male baseball pitchers and young female gymnasts: ●● the capitellum is relatively poorly vascularised,19 and therefore prone to ischaemia following repetitive

trauma ●● the anterolateral aspect of the capitellum is most commonly affected, and it is rarely bilateral

●● clinically: it usually affects males between the ages 12 to 15 years by which time the capitellar epiphysis is almost completely ossified, and presents with pain, swelling and tenderness over the lateral elbow

●● lesion stability is the most important prognostic factor in determining the likelihood of healing with conservative management21

●● early stages: may show only marrow oedema (Fig. 2.9a), followed later by focal low T1W SI and high T2W SI with surrounding sclerosis (Figs 2.9b, c)

●● instability: is suggested by a lesion surrounded by cysts (Fig. 2.10a) or a complete rim of hyperintense fluid on T2W images between the lesion and underlying bone marrow (Fig. 2.10b):

● an enhancing rim between the lesion and surrounding bone on post-contrast MRI

● extension of injected contrast around the lesion on MR arthrography ● an osteochondral loose body (Figs 2.10c, d) ● the sensitivity of MRI for detecting unstable lesions reaches 100% when there is a combination of

a high T2W SI rim, cysts, high T2W SI cartilage fracture line and fluid-filled OCD23 ●● following contrast: complete enhancement of the lesion indicates that it is viable, which is associated with

a favourable clinical outcome following conservative treatment: ● marginal or poor enhancement is suggestive of fragment instability24

●● identification of loose bodies:25 in a comparative study with arthroscopy as gold standard, non-arthrographic MRI has a sensitivity and specificity of 88-100% and 20-60% respectively:

● MRI is much more accurate in the diagnosis of loose bodies in the posterior joint compartment (Fig. 2.10d)

●● stress fractures of the olecranon process of the ulna: are usually the result of extension overload, and are described in upper-limb dominated sports such as tennis, baseball, gymnastics and weight-lifting

●● they affect the posteromedial aspect of olecranon with resulting posteromedial elbow pain ●● MRI findings:

●● marrow oedema-like SI in the posteromedial olecranon indicative of a stress response ●● a focal hypointense line extending to the cortex, indicative of a stress fracture with associated oedema

(Fig. 2.11) ●● in the adolescent overhead throwing athlete, marrow oedema may be seen within and surrounding

the olecranon physis ●● occasionally, oedema is present within the radial head, while the UCL is always intact

●● the sublime tubercle: represents the tip of the medial aspect of the base of the coronoid process of the ulna ●● avulsion injury of the sublime tubercle is described in baseball players, and presents with acute onset medial

elbow pain during throwing ●● MRI findings:

●● a small avulsion fracture of the tip of the sublime tubercle, which is optimally demonstrated on GRE sequences ●● it may be associated with a mid-substance injury to the UCL

●● medial epicondylar apophysitis: also called ‘Little League’ elbow, is a valgus stress overuse injury due to repetitive microtrauma to the medial epicondylar growth plate seen in baseball pitchers younger than 10 years of age

●● prior to its fusion, the medial epicondylar physis is weaker than the UCL and is therefore more frequently injured secondary to repeated valgus stress

●● MRI findings: ●● high SI, especially fluid SI, along the physis is characteristic ●● chronic physeal stress appears as widening and irregularity of the physis and is best assessed with coronal

GRE sequences ●● it may be associated with marrow oedema or fragmentation of the medial epicondylar apophysis

Occult Fractures ●● MRI may demonstrate occult elbow fractures in both children and adults ●● in children: MRI has demonstrated occult fractures in 22-57% and soft-tissue injuries in 62% of patients with

traumatic elbow effusions ●● in adults: MRI has demonstrated occult fractures in 47-100% and soft-tissue injuries in 16-24% of patients

with traumatic elbow effusions (Figs 2.12a-e): ●● the majority of patients without fractures had post-traumatic bone bruising

●● MRI in paediatric elbow fractures:32 MRI is useful in assessing radiographically identified fractures and may demonstrate occult injuries (Fig. 2.12f), including: ●● transphyseal fracture extension, extension along the physis, bone bruising, associated ligament/muscle injury ●● however, additional MR findings did not change patient management

●● the joint capsule: invests all 3 elbow articulations to form a single continuous joint space and comprises 2 layers, a deep synovial lining and a superficial fibrous layer

●● intra-capsular fat pads: 3 major fat pads are located between the 2 layers of the capsule: ●● the anterior capitellar and trochlear fat pads are located within the corresponding fossae (Figs 2.13a, b) ●● the posterior fat pad lies within the olecranon fossa (Fig. 2.13b)

●● capsular attachments: ●● anterior: to the distal humerus at the superior margin of the coronoid and radial fossae, and to the coronoid

process of the ulna (Fig. 2.13c) ●● posterior: to the distal humerus just proximal to olecranon fossa ●● medial: to the medial margin of the olecranon and trochlear notch ●● lateral: along the lateral margin of the trochlear notch and annular ligament

●● capsular recesses:4 5 are recognised: ●● the anterior humeral recess: located anteriorly and composed of the radial fossa (Fig. 2.14a) and coronoid

recess (Fig. 2.14b) ●● the olecranon recess: the largest and found along the posterior margin of the joint, having 3 components,

superior (Figs 2.14a, b), medial and lateral (Fig. 2.14c) ●● the annular (periradial) recess: located anteriorly where the capsule passes beneath the annular ligament

(Fig. 2.14d) ●● the medial and lateral collateral ligament recesses: extensions of the olecranon recess along either side of

the olecranon process and limited by the ulnar and radial collateral ligaments respectively (Fig. 2.14e)

(Figs 2.15a, b), and is almost always visible on conventional MRI (~98%), measuring up to 3 mm in craniocaudal dimension in asymptomatic individuals13

●● other synovial plicae include: ● the posterior plica, which is a synovial fold of the superior lateral olecranon recess, measuring up

to 3 mm in asymptomatic subjects and demonstrated in 28% and 73% of non-locking elbows on conventional MRI and MR arthrography respectively35 (Fig. 2.15c)

●● a snapping sensation at the elbow is not uncommon and can be due to extra-articular or intra-articular causes

●● extra-articular causes: include subluxation of the medial head of triceps or the ulnar nerve ●● intra-articular causes: include synovial folds,36,41 a torn/redundant annular ligament,41 and loose bodies ●● elbow synovial fold syndrome:35 is an uncommon condition that presents with symptoms suggestive of a loose

body, in which a thickened, hypertrophied and fibrotic plica may prevent full elbow extension ●● thickening of the radiocapitellar plica in symptomatic individuals has been referred to as a lateral synovial

fringe,42 giving rise to the term ‘synovial fringe syndrome’ ●● snapping plicae may be associated with chondromalacia of the anterolateral radial head43 ●● clinically: there may be a history of previous trauma, and snapping typically occurs between 90-110°

of flexion ●● MRI findings:

●● conventional MRI studies often show no abnormality, but non-contrast MRI with the use of microscopy coils has been reported to show synovial folds36

●● synovial fringe syndrome: a radiocapitellar plica thicker than 2.6 mm is reported in 67% (Fig. 2.15e), although size criteria alone is not entirely specific, as this thickness is also observed in 13% of controls39

●● in patients with elbow synovial fold syndrome, a thickened posterior plica in the olecranon recess has also been described, with mean thickness of 3.1 mm (range 2-5 mm)

●● the medial collateral ligament (UCL): comprises three distinct components, the anterior (oblique) bundle, posterior bundle and transverse bundle

●● the anterior bundle:45,46 is the major stabiliser against valgus and internal rotatory stress, being optimally demonstrated on coronal MR images: ●● it arises from a broad-based origin on the antero-inferior aspect of the medial epicondyle (Fig. 2.16a),

where interdigitation of fat within the proximal ligament may result in focal increased SI (Fig. 2.16b), a phenomenon that is reduced by imaging in the 20° posterior coronal oblique plane4

●● focal linear increased SI deep to the humeral attachment is caused by normal invagination of joint synovium, which could mimic partial tearing

●● it inserts into the sublime tubercle at the medial aspect of the base of the coronoid process of the ulna, the insertion being either at the joint margin (Fig. 2.16a) or up to 3 mm distal to the joint line (Fig. 2.16c), potentially mimicking a partial avulsion of the ligament45

●● the posterior bundle: is a secondary stabiliser against valgus and internal rotatory stress at 120° elbow flexion, and represents a fan-shaped thickening of the posterior capsule: ●● it originates from the posterior surface of the medial epicondyle, and inserts on the medial aspect of

the olecranon process of the ulna, being optimally demonstrated on axial MR images (Fig. 2.16d)

●● the transverse bundle: is also termed the ligament of Cooper, and represents a thickening of the medial capsule between the coronoid process and the tip of the olecranon process: ●● it does not contribute to joint stability and is not routinely identified on MRI

●● anatomical variants: an accessory (extra) bundle of the UCL is identified in approximately 25% of individuals and extends from the posteromedial aspect of the capsule to the transverse bundle

●● UCL injury: results in valgus instability of the elbow and may occur following a fall on the outstretched hand, acute elbow dislocation,50 or sports associated with repetitive overhead action, including tennis, weightlifting, baseball and javelin

●● the majority are full-thickness tears of the anterior bundle, while partial-thickness tears most commonly involve the deep surface of the anterior bundle

●● injury most commonly occurs in the mid-substance, followed by avulsion from the ulnar attachment, and less commonly from the epicondylar attachment

●● avulsion of the sublime tubercle may occur rather than tearing of the ligament (see earlier) ●● clinically: UCL injury manifests with signs and symptoms of medial elbow instability, including medial

elbow pain and opening of the joint on valgus stress: ●● symptoms of ulnar neuropathy may also be present

●● the differential diagnosis includes: medial epicondylitis, flexor-pronator tendon tears, flexor-pronator fascial compression syndrome, valgus extension overload syndrome (VEOS) and ulnar neuropathy

●● MRI findings: ●● a full-thickness tear manifests as focal discontinuity of the ligament, which is replaced by T2W

hyperintensity due to oedema and haemorrhage (Fig. 2.17a)

●● a partial thickness tear manifest as abnormal morphology (thickening, laxity) and increased SI of the UCL, with periligamentous oedema (Fig. 2.17b)

●● acute tears may be associated with lateral compartment (radiocapitellar) bone bruises, or a strain of the common flexor tendon origin

●● low-grade injuries appear as periligamentous oedema, but the majority of ligament fibres remain intact ●● MRI has a sensitivity and specificity of 100% for diagnosing full-thickness tears of the anterior bundle,

and 57% and 100% respectively for partial-thickness tears of the anterior bundle ●● MR arthrography findings:8

●● complete tears show extravasation of injected contrast medium at the site of ligament rupture ●● partial deep surface tears are optimally demonstrated by coronal MR arthrography:

● demonstrates irregularity of the deep surface of the ligament ● extension of contrast medium distally from the joint line beneath the ulnar attachment of the ligament

producing the ‘T-sign’ (Fig. 2.17c) ●● sensitivity and specificity for partial-thickness tears improves to 86% and 100% respectively for MR arthrography ●● indirect MR arthrography demonstrates focal enhancement at the site of the tear10

●● VEOS: is a common condition seen in throwing athletes ●● pathologically: the anterior bundle of UCL is intact but attenuated due to repetitive microtrauma from the

overhead throwing action: ●● a large valgus stress with brisk elbow extension during the late cocking and early acceleration phases

of overhead throwing results in the posteromedial olecranon tip impinging on the medial aspect of the olecranon fossa

●● posteromedial olecranon impingement leads to the development of medial olecranon osteophytes and chondromalacia of the posteromedial trochlea

●● osteophytes may fracture, forming intra-articular loose bodies

●● surgical treatment: of UCL insufficiency involves either ligament repair or reconstruction, with reconstruction being more commonly performed56

●● UCL reconstruction: is used to restore medial elbow stability and relieve medial elbow pain following UCL injury, usually performed in high level overhead throwing athletes

●● the ligament is typically sutured to an ipsilateral PL tendon graft and anchored in placed via a single ulnar and two medial epicondylar tunnels57

●● a normal graft should be taut and typically appears thickened compared with a native UCL ●● the intact graft can demonstrate variable signal intensity, although >70% are reported to have

a homogeneously low SI on T1W and T2W imaging (Figs 2.18a, b) ●● graft degeneration appears as diffuse intermediate signal and graft thickening on T1W imaging, as well as

fibre irregularity or discontinuity on T2W/STIR imaging (Fig. 2.18c) ●● MR arthrography findings:

●● graft tears are evident as sites of contrast material insinuation on FS T1W imaging and fluid signal intensity on T2W images

●● the lateral collateral ligament (LCL): consists of three distinct components, the radial collateral ligament, the annular ligament and the lateral band of the UCL

●● the radial collateral ligament (RCL): originates from the lateral epicondyle of the humerus and inserts into the fibres of the annular ligament, being optimally visualised on coronal MR images (Fig. 2.19a)

●● the annular ligament: is a thick fibrous band that completely encircles the radial head and stabilises the proximal radio-ulnar joint: ●● its anterior portion attaches to the anterior margin of the sigmoid notch, while the posterior portion

divides into several bands, which attach into the posterior margin of the sigmoid notch ●● it is optimally visualised on axial MR images (Fig. 2.19b)

●● the lateral band of the UCL (LUCL): together with the annular ligament, provides the majority of stability against varus and external rotatory stress: ●● it is present in 90% of individuals and originates from the lateral epicondyle of the humerus together with

the RCL, extending distally and obliquely to insert into the supinator crest of the proximal ulna ●● it is optimally visualised on coronal high resolution PDW FSE (Fig. 2.19c) or direct MR

arthrography (Fig. 2.19d) images as an oblique hypointense structure running posterior to the radial neck

●● anatomical variants: an accessory LCL is occasionally identified, and extends from the annular ligament to the supinator crest

●● RCL insufficiency: results in varus instability, which is less common than valgus instability ●● varus stress: may occur as an acute injury or due to elbow dislocation or subluxation:

●● post-operatively due to excessive release of the common extensor tendon or radial head excision ●● rarely as a repetitive stress injury

●● RCL tears: are most commonly full-thickness (Fig. 2.20a), and from the proximal attachment (Fig. 2.20b)

●● posterolateral rotatory instability (PRI): is due to a LUCL tear with an intact annular ligament, and results in: ●● posterior subluxation/dislocation of the radial head relative to the capitellum ●● secondary rotatory subluxation of the ulnohumeral joint

●● LUCL tears: most commonly occur at the lateral epicondylar attachment, and less commonly in the midsubstance

●● clinically: PRI manifests as chronic lateral elbow pain, a catching or snapping sensation with elbow movement and recurrent lateral instability

●● MRI findings: ●● discontinuity of LUCL from its proximal attachment, optimally seen on coronal images ●● posterior subluxation of the radial head with the arm supinated and elbow extended, optimally assessed on

sagittal images (Fig. 2.21)

●● a loose annular ligament: may be a cause of snapping elbow,35 and has been described in association with posterolateral elbow instability47

●● tears of the annular ligament: occur with subluxation or dislocation of the proximal radio-ulnar joint, and may be demonstrated on MR arthrography by escape of joint fluid from the region of the torn ligament (Fig. 2.22)

●● the anterior compartment muscles: include brachialis and biceps, which both flex the elbow ●● the brachialis muscle: arises from the anterior surface of the distal humerus (Figs 2.23a, b) and inserts via its

tendon into the base of the coronoid process of the ulna and the ulnar tuberosity (Figs 2.23a, c) ●● the biceps muscle: lies superficial to brachialis within the distal arm and is both a powerful supinator and

flexor of the elbow: ●● the distal biceps tendon is a paratenon-like extrasynovial structure without a tendon sheath, forming

6-7 cm above the elbow joint and running through the anterior aspect of the cubital fossa (Figs 2.24a, b) to insert into the posterior aspect of the radial tuberosity (Figs 2.24c, d)

●● cadaveric studies have shown that a large proportion of individuals have two independent muscle bellies, from the short and long heads of biceps respectively, with two distinct tendons, one for each muscle, inserting separately onto the radial tuberosity footprint:

● the tendon for the short head inserts slightly distally and anteriorly, whereas the tendon for the long head inserts more proximally65,66

●● the ventral surface of the tendon is flattened and the tendon rotates through 90° prior to its insertion: ● assessment of the distal tendon can be improved with the FABS position (see earlier)

●● the tendon is separated from the anterior aspect of the radial tuberosity by the bicipitoradial bursa ●● the distal biceps tendon gives rise to the bicipital aponeurosis (also termed lacertus fibrosus) (Fig. 2.24e),

which blends with the fascia covering the flexor-pronator group of muscles and may prevent proximal migration of the tendon following complete tendon rupture

●● distal biceps tendon rupture: classically occurs in sports associated with weight training and is much less common than injury to the proximal biceps tendon, accounting for 3-10% of biceps tendon ruptures: ●● it is usually due to a single traumatic event, with ruptures typically occurring 1-2 cm proximal to

the radial tuberosity, where there is commonly a zone of tendon hypovascularity associated with the development of degenerative hypoxic tendinopathy

●● ruptures may be complete or, less commonly partial, and only rarely occur at the musculotendinous junction

●● clinically: ruptures are seen in the dominant arm of males between 40-60 years of age: ● the muscle contracts proximally during elbow flexion with associated marked weakness of flexion and

supination, and a soft-tissue mass may be present in the antecubital fossa ●● MRI findings:

●● complete rupture: detachment of the tendon from the radial tuberosity (Fig. 2.25a) with increased T2W SI in the antecubital fossa due to oedema and haemorrhage (Fig. 2.25b):

● proximal retraction of the biceps tendon/muscle (Figs 2.25c, d)

● if the bicipital aponeurosis remains intact, little or no tendon retraction occurs (Figs 2.25e, f ), in which case tears may be difficult to identify

● additional features include marrow oedema in the radial tuberosity due to microavulsion, and fluid within the bicipitoradial bursa

●● partial rupture:67 increased intratendinous T2W SI, associated with tendon thickening (Fig. 2.25g) or attenuation:

● bicipitoradial bursitis and radial tuberosity marrow oedema are common, being seen in approximately 50% of cases (Fig. 2.25h)

●● a pseudotumour: of the distal biceps muscle has been described following chronic complete distal biceps tendon rupture (Fig. 2.25i)68

●● distal biceps tendinosis: is defined as intrasubstance degeneration and results from repetitive mechanical impingement of the poorly vascularised distal tendon between the radius and ulna

●● it is often seen in sports which involve weight training ●● it may predispose to tendon rupture and can coexist with partial tearing and bursitis ●● MRI findings:

●● swelling and hyperintensity of the distal tendon (Figs 2.26a, b) ●● chronic biceps tendinosis may be associated with:

● osseous proliferation at the radial tuberosity (Fig. 2.26c) ● supinator muscle oedema, and bursitis (Figs 2.26d, e) in the region of the distal tendon (bicipitoradial

or interosseous)

●● the posterior compartment muscles: include triceps, anconeus and anconeus epitrochlearis ●● the triceps muscle: consists of medial, lateral and long heads, which blend together to form a single

musculotendinous unit that inserts via the triceps tendon into the tip of the olecranon process of the ulna (Figs 2.27a-c): ●● rarely, part of the medial head may insert into the medial epicondyle, where it can compress the ulnar nerve ●● the tendon is separated from the olecranon process by the olecranon bursa ●● the muscle functions to extend the elbow

●● the anconeus muscle: arises from the posterior portion of the lateral epicondyle (Fig. 2.28a) and inserts into the posterolateral surface of the proximal ulna: ●● it covers the lateral aspect of the radial head and annular ligament (Fig. 2.28b) but has little role in

stabilising the elbow joint ●● the anconeus epitrochlearis muscle: is an accessory muscle present in less than a third of elbows:

●● it typically measures 2.5 × 2 × 1 cm and replaces the cubital tunnel retinaculum, arising from the medial epicondyle and inserting into the tip of the olecranon process of the ulna (Fig. 2.28c)

●● triceps tendon rupture: is a rare injury, which may occur following a direct blow or a fall on the outstretched hand: ●● it is also seen in sports requiring repetitive elbow extension and may be associated with radial head

fracture ●● full-thickness tears are more common than partial-thickness tears and typically occur at the insertion into

the olecranon process ●● risk factors include: renal insufficiency, hyperparathyroidism, Marfan’s syndrome, osteogenesis imperfecta

tarda, olecranon bursitis and steroid use ●● MRI findings:

●● full-thickness tears: appear as fluid-filled discontinuity of the tendon from the olecranon process (Figs 2.29a, b)

●● partial-thickness tears: appear as a fluid-filled partial defect within the tendon (Figs 2.29c, d) and surrounding oedema:

● disruption and retraction of the superficial layer of the tendon and preservation of the deep layer (Fig. 2.29e) is characteristic of partial-thickness tears72

●● rarely, an avulsion fracture of the tip of the olecranon may occur (Figs 2.29f, g)

●● the medial head of the triceps muscle or tendon may dislocate over the medial epicondyle resulting in snapping, either during elbow flexion or elbow extension from the flexed position

●● clinically: this manifests as painless or painful elbow snapping, with or without ulnar neuropathy ●● predisposing factors: include a congenital or acquired prominent medial head of triceps, an accessory triceps

tendon and developmental or post-traumatic cubitus varus ●● MRI findings:74

●● dislocation may be demonstrated by imaging the elbow in extension followed by full flexion ●● a subluxing or dislocating medial head of triceps and/or ulnar nerve will be identified medial or anterior

to the medial epicondyle in the flexed position

●● distal triceps tendinosis: or posterior epicondylitis, is far less common than medial or lateral epicondylitis (see later), and results from overuse and repetitive microtrauma in overhead throwing athletes, as well as weightlifters

●● it is often associated with other chronic posterior elbow disorders, including olecranon bursitis or a stress reaction of the olecranon

●● MRI findings: ●● thickening of the distal triceps tendon, with intermediate SI on T1W images and intermediate/increased

SI on T2W and STIR sequences (Figs 2.30a, b)

●● oedema of the anconeus epitrochlearis: is a condition of uncertain aetiology, and has also been reported as a potential cause of medial elbow pain

●● MRI findings: ●● increased muscle SI seen on FS T2W FSE/STIR images

●● the medial compartment muscles: include pronator teres (PT) and the 4 superficial flexors, flexor carpi radialis (FCR), palmaris longus (PL), flexor carpi ulnaris (FCU) and flexor digitorum superficialis (FDS) (Fig. 2.31a), which function to flex the wrist and pronate the forearm: ●● PT arises mainly from the medial humeral epicondyle (humeral head) (Fig. 2.31b) and the medial aspect

of the coronoid process (ulnar head) ●● FDS also arises from the proximal radius ●● PL may be absent in 13% of cases ●● FCU has 2 heads arising near the cubital tunnel, from the medial part of the common flexor tendon (CFT)

and the medial aspect of the olecranon (Fig. 2.31c) ●● the arcuate ligament: a fibrous arch, also termed Osborne’s band or the cubital tunnel retinaculum, runs

between the 2 heads of FCU and forms the roof of the cubital tunnel: ●● it may be absent in 23% of cases

●● the CFT: gives rise to the superficial flexor muscles and part of PT at the medial epicondyle, and normally appears diffusely hypointense on all pulse sequences (Figs 2.31b and 2.32a, b): ●● however, it may show thickening and intermediate SI on T1W and T2W images in the absence of

symptoms of medial epicondylitis76 ●● the deep flexor muscles: include flexor digitorum profundus (FDP) (Fig. 2.31a) and flexor pollicis longus

(FPL), which both originate from the proximal ulna, distal to the cubital tunnel

●● medial epicondylitis: is also termed ‘golfers elbow’, but other sports associated with this injury include racquet and throwing sports, bowling, archery, weightlifting and swimming: ●● although the term suggests inflammation of the epicondyle, osseous inflammatory changes such as marrow

oedema are infrequently seen on MRI ●● pathologically: it results from flexor tendinosis due to repetitive valgus and flexion movements, with changes

being most commonly identified in the PT and FCR tendons ●● clinically: it is usually seen in athletes with chronic medial elbow pain and point tenderness over the common

flexor origin (CFO): ●● it is far less common than lateral epicondylitis, although both may occur in some individuals, and it may be

associated with ulnar nerve symptoms ●● in the acute setting, athletes may present following injury with the so-called ‘flexor-pronator strain’3

●● tendinosis manifests as increased SI and swelling at the CFO adjacent to the medial epicondyle, best seen on coronal (Figs 2.33a, b) and axial (Fig. 2.33c) images

●● in the relatively acute stage of symptoms, MRI may be normal ●● additional features: increased SI within the medial epicondyle (Fig. 2.33d) and adjacent muscles, as well

as ulnar neuropathy (see later) ●● increased T2W SI within the tendon and in the surrounding muscles is specific for symptomatic medial

epicondylitis ●● in the skeletally immature, medial epicondylitis must be differentiated from overuse injury to the medial

epicondylar apophysis (‘Little League’ elbow – see earlier) ●● CFT tears may also occur:

● full-thickness tears: of the tendon appear as a fluid-filled gap at the tendon-epicondyle attachment (Fig. 2.33e) ● partial-thickness tears: manifest as thinning of the tendon with surrounding fluid (Fig. 2.33f)

●● fluid SI changes around/within the tendon may also be due to recent steroid or anaesthetic injections ●● in severe cases, injury to the UCL may occur, especially the anterior band (Fig. 2.33d) ●● in ‘flexor-pronator strain’, a feathery pattern of increased T2W SI is seen within the bellies of the flexor-

pronator muscles ●● MR arthrography findings:10

●● indirect MR arthrography shows enhancement at the site of tendinopathy (Fig. 2.33g) and within the epicondyle

●● the lateral compartment muscles: can be divided into 3 components, the superficial group, the common extensors and supinator, which all function to extend the wrist joint and supinate the forearm

●● the superficial group: includes brachioradialis and extensor carpi radialis longus (ECRL): ●● brachioradialis: originates from the supracondylar ridge of the humerus (Fig. 2.34a) and inserts into

the radial styloid ●● ECRL: originates from the supracondylar ridge of the humerus distal to brachioradialis (Fig. 2.34a) and

inserts into the base of the second metacarpal ●● the common extensor group: includes extensor carpi radialis brevis (ECRB), extensor digitorum (ED),

extensor digiti minimi (EDM) and extensor carpi ulnaris (ECU) (Figs 2.34b, c): ●● ECRB, ED, EDM and ECU: all arise from the lateral epicondyle via the common extensor tendon (CET)

(Figs 2.34b and 2.35a, b) ●● supinator: has a bulky deep component and a slim superficial component:

●● it arises from the anterior aspect of the lateral epicondyle and the supinator crest of the ulna, and extends distally and laterally to insert into the radial shaft (Figs 2.36a, b)

●● the posterior interosseous nerve lies between the superficial and deep components of supinator, which can occasionally be differentiated by the presence of a thin layer of fat (Fig. 2.36c)

●● lateral epicondylitis: is the commonest cause of sports related elbow pain, also being termed ‘tennis elbow’: ●● it may also be an occupational injury associated with carpentry and a variety of musical instruments,

such as drums and string instruments (violin and cello) ●● pathologically: it results from repetitive varus stress at the common extensor origin (CEO) causing tendinosis,

tenosynovitis and partial/complete tears, which most commonly affect the ECRB and ED tendons at the lateral epicondyle

●● clinically: it is most commonly seen in the 40-60 year age group and presents with chronic lateral elbow pain and point tenderness over the lateral epicondyle

●● the role of MRI: is not to establish the diagnosis, which is usually clinically evident, but rather to exclude concomitant causes of lateral elbow pain in patients who have not responded to conservative management

●● MRI findings: ●● tendinosis: manifests as swelling and increased intratendinous SI on T1W/PDW FSE (Fig. 2.37a) and

T2W/STIR images (Figs 2.37b, c), with the greatest SI abnormality involving the region of the ECRB tendon

●● partial tears: manifest as tendon thinning with associated adjacent fluid SI (Fig. 2.37d) ●● full-thickness tears: manifest as a complete fluid-filled gap at the tendon-epicondyle interface ●● associated features: include oedema in the adjacent lateral epicondyle (Fig. 2.37e) and increased T2W SI

in the anconeus muscle (Fig. 2.37f): ● fluid in the radiohumeral bursa ● injury to the LUCL has been reported in >90% of patients with lateral epicondylitis79 ● associated injuries of the LCL (Fig. 2.37d) and UCL have also been reported, but are less commonly

encountered ●● MR arthrography findings:

●● indirect MR arthrography shows enhancement at the site of tendinopathy (Fig. 2.37g), and within the epicondyle10

●● the elbow/cubital bursae: include the bicipitoradial, interosseous and olecranon ●● the bicipitoradial bursa:80 covers the anterior aspect of the radial tuberosity, lying between the tuberosity

and the distal biceps tendon insertion, and functions to reduce friction between these structures ●● the interosseous bursa: is identified in approximately 20% of cases and is located in the medial aspect of the

antecubital fossa, adjacent to biceps tendon and brachialis muscle: ●● it occasionally communicates with the bicipitoradial bursa

●● the olecranon bursae: 3 posterior bursae are reported: ●● superficial olecranon bursa: lies in the subcutaneous tissues between the skin and olecranon process ●● deep intratendinous bursa: lies within the substance of triceps near its insertion into the olecranon ●● deep subtendinous bursa: lies deep to the triceps tendon near its insertion

●● clinically: patients present with a mass in the antecubital fossa, which may be painful, and restricted elbow movement: ●● the enlarged bursa may result in compression of adjacent nerves, including the superficial or deep branches

of the radial nerve, but not the median nerve ●● MRI findings:

●● a lobular mass in the antecubital fossa with partial or complete envelopment of the distal biceps tendon (Figs 2.38a, b)

●● the mass is hypointense to muscle on T1W (Fig. 2.38a) and hyperintense on T2W/STIR (Fig. 2.38b) showing variable rim enhancement following gadolinium (Fig. 2.38c), the degree of enhancement being related to the degree of active synovitis

●● it is smooth or irregular in outline, with internal septa and/or heterogeneous hypo-intensity due to chronic synovitis (Figs 2.38d, e)

●● associated findings: ● swelling and hyperintensity of the distal biceps tendon due to tendinosis ● localised cortical bone resorption has been described in cubital bursitis complicating rheumatoid

arthritis (Fig. 2.38a)83

●● olecranon bursitis: may be classified as aseptic or septic ●● aseptic olecranon bursitis: is associated with repetitive trauma, inflammatory arthropathy, obesity, prolonged

pressure against the elbow in patients on haemodialysis (dialysis elbow) and trauma (elbow fracture, triceps tendon tear)

●● septic bursitis: accounts for approximately 33% of cases of olecranon bursitis and may be post-traumatic or occur in immunocompromised patients, with 90% due to Staphylococcus aureus

●● clinically: patients present with a soft posterior elbow mass, which may be painful ●● MRI findings:

T1W (Fig. 2.39a) and hyperintense on T2W (Fig. 2.39b) ●● the mass shows rim enhancement following gadolinium ●● associated features: include elbow joint effusion, surrounding soft-tissue oedema, thickening of the triceps

tendon and marrow oedema in the olecranon ●● no single feature discriminates aseptic from septic bursitis ●● however, marked soft-tissue oedema, increased lobulation, olecranon marrow oedema and thickening of

the triceps tendon are more suggestive of infection (Figs 2.40a, b)

●● the radial nerve: is a continuation of the posterior cord of the brachial plexus ●● at the level of the elbow joint, it runs within the radial tunnel, a space that is ~5 cm in length, extending from

the capitellum proximally to the supinator muscle distally and bounded by brachioradialis anterolaterally, brachialis anteromedially and the joint capsule posteriorly (Fig. 2.41a)

●● at the proximal margin of supinator, it divides into 2 major branches (Fig. 2.41b), the posterior interosseous nerve (PIN) and the superficial radial nerve

●● the PIN: passes between the superficial and deep heads of supinator and extends distally in the posterior compartment of the forearm, together with the posterior interosseous artery: ●● the proximal edge of the superficial head of supinator may form a fibrous arch, the arcade of Frohse,

through which the nerve passes, this being present in 35-65% of individuals and may be seen on MRI as a low SI band overlying the supinator muscle (Fig. 2.41c)

●● in the elbow region, the nerve innervates the common extensor and anconeus muscles ●● the superficial radial nerve: passes distally between supinator and brachioradialis (Fig. 2.41d) and provides

sensory innervation to the dorsal soft tissues of the forearm and hand

●● PIN syndrome: is also termed the supinator syndrome and results from compression of the PIN ●● repetitive pronation-supination movements, as seen in violinists and swimmers can predispose to

pathological PIN compression89 ●● 5 possible compression sites are described, the commonest being the arcade of Frohse:

●● others include: the anterior capsule of the radiocapitellar joint, small vessels from the recurrent radial artery that cross the nerve (the leash of Henry), the fibrous edge of the ECRB muscle and the distal margin of supinator

●● other causes of compression neuropathy include: tumours, ganglion cysts, radiocapitellar synovitis, bicipitoradial bursitis, radial head trauma (fractures/dislocations) and iatrogenic, following internal fixation of the proximal radius

●● clinically: PIN syndrome manifests as the slow onset of pain (without significant sensory loss) and loss of motor function in those muscles innerved by the PIN, mainly the extensor group of muscles, resulting in wrist drop

●● MRI findings: ●● denervation oedema/atrophy of the supinator and extensor muscles (Figs 2.42a, b) ●● the underlying cause (Figs 2.43a, b)

●● radial tunnel syndrome: is due to compression of the PIN in the radial tunnel ●● pathologically: it results from dynamic stress caused by passive compression from repeated elbow flexion,

pronation and supination

●● clinically: it manifests as activity related radial side forearm pain with no motor loss, pain on resisted supination of the forearm and pain on resisted middle finger extension: ●● it may be associated with lateral epicondylitis in ~5% of cases ●● relief of symptoms may occur with local anaesthetic injection into the radial tunnel

●● MRI findings: ●● may be optimally demonstrated with the forearm pronated, the muscle denervation pattern depending

upon the site of compression: ● denervation of triceps, anconeus, brachioradialis and ECRL indicates radial nerve compression prior to

its division into the PIN and superficial radial nerves ●● denervation changes are most commonly seen in supinator (44%), or the proximal forearm muscles (12%) ●● isolated oedema of the PT is a rare occurrence (4%) ●● a mass lesion may be seen along the route of the PIN ●● the nerve itself does not usually demonstrate increased SI on T2W

●● the median nerve: is formed from branches of the medial and lateral cords of the brachial plexus ●● at the level of the humeral epicondyles, it runs between the PT and brachialis (Fig. 2.44a) ●● within the antecubital fossa, the nerve lies deep to the bicipital aponeurosis, medial to the biceps

tendon and brachial artery (Fig. 2.44b), and extends distally between the 2 heads of PT (in 80% of individuals)

●● it innervates the PT and the common flexor muscles, and gives rise to the anterior interosseous nerve (AIN), its final major branch at the inferior border of PT

●● the AIN courses distally along the volar aspect of the interosseous membrane between the FDP and FPL muscles

●● in the absence of fat, the median nerve is difficult to visualise on axial MR images

●● pronator syndrome: is due to compression of the median nerve at the elbow or in the proximal forearm ●● 4 potential sites of compression are described:

●● the supracondylar process of the humerus (avian spur): a bony prominence arising from the anteromedial aspect of the distal humerus, 5-7 cm proximal to the medial epicondyle and present in approximately 3% of individuals:

● a fibrous band (the ligament of Struthers) may extend from the spur to the medial epicondyle, forming a fibro-osseous tunnel through which the median nerve, and occasionally the brachial artery pass

● this represents the least common site of compression ●● a thickened bicipital aponeurosis, or an accessory fibrous band associated with a 3rd head of the biceps

muscle ●● between the humeral (superficial) and ulnar (deep) heads of the PT muscle, the commonest site of

compression neuropathy, due to fibrous bands (found in 50% of individuals) or prolonged pronation of the forearm

●● at the FDS muscle: the second commonest site of compression neuropathy, due to a fibrous band arising 2 cm distal to the PT muscle

●● other causes of compression neuropathy: include an accessory bicipital aponeurosis, intra-articular entrapment following closed reduction of elbow dislocation, aberrant vessels and accessory muscles (the accessory head of FPL [Gantzer’s] muscle and palmaris profundus)

●● clinically: patients experience pain in the volar aspect of the elbow and forearm, which is exacerbated by repetitive pronation and grasping (such as in tennis), and paraesthesia in the thumb to middle fingers

●● MRI findings: ●● the FOV must cover from the distal one-third of the arm to FDS in the forearm ●● denervation oedema/atrophy of the flexor-pronator muscle group and evidence of the underlying cause ●● a low SI band due to the ligament of Struthers or a soft-tissue mass

●● AIN syndrome: is due to compression of the AIN in the proximal forearm ●● causes of compression neuropathy: include entrapment by the tendinous origin of PT, PL, FCR, Gantzer’s

muscle (see earlier), aberrant radial artery, bicipitoradial bursitis and iatrogenic causes ●● most cases are non-mechanical and occur as part of Parsonage-Turner syndrome (see earlier) ●● clinically: purely motor palsy with weakness of flexion of the interphalangeal joint of the thumb, or the distal

interphalangeal joint of the index finger (due to FPL or FDP dysfunction), which can mimic tendon rupture ●● MRI findings:

●● denervation oedema/atrophy of the pronator quadratus muscle is always seen, and FDP and FDL are less commonly involved91

●● the ulnar nerve: arises from the medial cord of the brachial plexus ●● proximal to the elbow, the nerve runs posterior to the medial epicondyle (Fig. 2.45a) ●● at the level of the elbow joint, the nerve runs through the cubital tunnel:

●● the roof is formed by the cubital tunnel retinaculum (arcuate ligament) (Fig. 2.45b) ●● the floor of the cubital tunnel is formed by the posterior bundle of the UCL (Fig. 2.45c) ●● within the cubital tunnel, the nerve is surrounded by fat ●● distally, the nerve passes between the 2 heads of FCU (Fig. 2.45d)

●● in the proximal forearm, the ulnar nerve innervates the FCU and medial part of the FDP muscles

●● sites of potential compression of the ulnar nerve in the elbow and proximal forearm region include: ●● just proximal to the elbow joint: by the medial head of triceps ●● in the cubital tunnel: the commonest site ●● less commonly: by Osborne’s fascia (a fibrous band connecting the proximal edge of FCU to the medial

epicondyle) and the deep flexor-pronator aponeurosis, through which the ulnar nerve exits the cubital tunnel

●● cubital tunnel syndrome (CTS): is the commonest neuropathy of the ulnar nerve at the elbow and may be classified as: ●● physiologic: due to the normal decrease in volume of the cubital tunnel during elbow flexion ●● acute or subacute external compression: following direct force applied to the cubital tunnel ●● chronic compression: due to mass lesions including bursae, medial elbow ganglia93 (account for 8% of cases

of CTS, is the third commonest cause and is almost always associated with OA), inflammatory synovitis, osteophytes and loose bodies, joint deformity such as cubitus valgus and an accessory muscle, the anconeus epitrochlearis94

●● 2 age ranges are described: 20-30 years (typically post-traumatic) and 50-60 years (typically associated with osteoarthritis)

●● clinically: CTS manifests as paraesthesia along the ulnar aspect of the hand, little and ring fingers, medial elbow and forearm pain, with weakness of the muscles innervated by the ulnar nerve

●● MRI findings: ●● swelling and/or hyperintensity of the ulnar nerve within the cubital tunnel on FS PDW/T2W FSE images

(Figs 2.46a, b);95 this should be distinguished from an engorged deep recurrent ulnar vein, which lies just lateral to the ulnar nerve in the cubital tunnel

●● denervation of muscles on the ulnar side of the forearm and hand, including FCU and FDP ●● any underlying cause such as osteophytes, synovitis or soft-tissue masses

● technique: high resolution axial T1W, STIR and FS T2W sequences through the ulnar nerve, the latter with higher echo times (TE >70) than with conventional elbow MRI95

● mean ulnar nerve size is significantly larger in symptomatic individuals (0.12 cm2) compared with control subjects (0.06 cm2)

Ulnar Nerve Subluxation/Dislocation ●● subluxation/dislocation of the ulnar nerve: may be asymptomatic, being reported in 10-16% of individuals ●● however, it may also lead to secondary friction neuritis and ulnar neuropathy ●● ulnar nerve dislocation may be secondary to:

●● congenital absence, tear or laxity of the arcuate ligament ●● a hypoplastic trochlea or post-traumatic cubitus valgus

●● it may also be associated with snapping triceps syndrome: dislocation of the medial head of triceps over the medial epicondyle

●● MRI findings: ●● a dislocated ulnar nerve, optimally visualised on axial images (Fig. 2.47) ●● a subluxing nerve, optimally appreciated with the elbow imaged in flexion ●● absence of the arcuate ligament may be noted