Elbow magnetic resonance imaging: imaging anatomy and evaluation.

REVIEW ARTICLE

Elbow Magnetic Resonance Imaging: Imaging Anatomy and Evaluation Jennifer Hauptfleisch, MBChB, FRCR, Collette English, BMBS, FRCR, and Darra Murphy, MBBCh, BAO, FFR(RCSI), FRCPC Abstract: The elbow is a complex joint. Magnetic resonance imaging (MRI) is often the imaging modality of choice in the workup of elbow pain, especially in sports injuries and younger patients who often have either a history of a chronic repetitive strain such as the throwing athlete or a distinct traumatic injury. Traumatic injuries and alternative musculoskeletal pathologies can affect the ligaments, musculotendinous, cartilaginous, and osseous structures of the elbow as well as the 3 main nerves to the upper limb, and these structures are best assessed with MRI. Knowledge of the complex anatomy of the elbow joint as well as patterns of injury and disease is important for the radiologist to make an accurate diagnosis in the setting of elbow pain. This chapter will outline elbow anatomy, basic imaging parameters, compartmental pathology, and finally applications of some novel MRI techniques. Key Words: elbow, anatomy, magnetic resonance imaging, sports injury, imaging parameters (Top Magn Reson Imaging 2015;24: 93–107)

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he elbow is a complex joint and often the source of pain not only to radiologists but also to family physicians, sports medicine specialists, orthopedic surgeons, and rheumatologists, not to mention the patients themselves. Traumatic injuries affecting musculotendinous, cartilaginous, and osseous structures can all contribute to discomfort, and complex anatomic and physiologic structures crossing the joint including the ligaments, vessels, and nerves all play a role. Magnetic resonance imaging (MRI) is often the imaging modality of choice in the workup of elbow pain, especially in younger patients who often have either a history of a chronic repetitive strain such as the throwing athlete or a distinct traumatic injury. Knowledge of the complex anatomy of the elbow joint as well as patterns of injury and disease is important for the radiologist to make an accurate diagnosis in the setting of elbow pain. This article outlines some basic imaging parameters and then is divided by compartment followed by separate sections on the upper-limb nerves and finally applications of some novel MRI techniques.

OPTIMIZING IMAGE ACQUISITION Magnetic resonance imaging evaluation of the elbow begins with proper patient positioning. Typically, the patient is placed in the supine position with the arm held in the anatomical position. This position has the advantage of comfort for the patient, thereby minimizing motion. A disadvantage of this position is that the elbow joint is away from the isocenter of the magnet, and image quality can be degraded because of decreased signal to noise and field inhomogeneity. Many radiologists prefer imaging in From the Department of Radiology, St Paul's Hospital, Vancouver, British Columbia, Canada. Reprints: Darra Murphy, MBBCh, BAO, FFR(RCSI), FRCPC, Department of Radiology, St Paul's Hospital, 1081 Burrard St, Vancouver, British Columbia, Canada (e‐mail: [email protected]). The authors report no conflicts of interest. Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.

the prone position with the shoulder extended and the arm raised above the head (“superman” position). Dedicated surface coils help to improve image quality. Coronal, axial, and sagittal images are acquired using T1- and T2-weighted images (Table 1). It is important to include the radial tuberosity in the axial images as the biceps tendon attaches here. The distal biceps tendon has an oblique course, and partial volume averaging can be problematic. The extent of the distal tendon can be better seen with the flexed abducted supinated view.1 In this position, the elbow is flexed with the shoulder abducted and the forearm supinated.

MEDIAL COMPARTMENT Anatomy The pronator teres and the flexors of the hand and wrist arise from the medial epicondyle as the common flexor tendon. The common flexors mass includes the flexor carpi radialis, palmaris longus, flexor carpi ulnaris, and flexor digitorum superficialis, and its primary function is as a flexor of the wrist and hand. The pronator teres has 2 origins, one at the humeral head and the other at the medial coronoid process, and it functions as a pronator of the forearm. The medial collateral ligaments (MCLs) lie deep to the common flexor origin (CFO) and consist of 3 bundles: the anterior, posterior, and transverse bundles. The largest and most important component is the anterior bundle, providing the most stability, particularly to a valgus stress. It is a broad ligament arising from the inferior margin of the medial epicondyle and inserting into the sublime tubercle along the medial coronoid margin (Fig. 1). The posterior bundle is a fan-shaped structure that arises from the medial epicondyle and inserts into the medial aspect of the olecranon. It is a constraint against internal rotation. The transverse bundle has a horizontal orientation and extends between the olecranon and the coronoid process. It does not contribute to elbow stability. Both the posterior and transverse bundles are not well demonstrated on MRI and are of overall little importance. Variant osseous anatomy to be aware of includes a pseudolesion of the trochlea2 and the supracondylar process, a horn-shaped bony excrescence arising from the anteromedial aspect of the distal humerus, found in 0.2% to 3% of subjects.3

MCL Trauma Medial collateral ligament trauma is most commonly seen in athletes participating in overhead sports such as baseball, tennis, volleyball, javelin, and football and is due to the chronic repetitive valgus stress of throwing motion. Injury of the MCL occurs in the late cocking and early acceleration phases of the throwing cycle where there is medial distraction and lateral impaction with the elbow flexed and the forearm supinated.4–6 The anterior band of the MCL is the main stabilizer in the extremes of motion, and significant and repetitive valgus stress often leads to chronic microtrauma. Medial collateral ligament injury from a single acute event may also occur but is much less common than chronic repetitive injury.

Topics in Magnetic Resonance Imaging • Volume 24, Number 2, April 2015

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TABLE 1. Standard Pulse Sequences for MRI Examination of the Elbow Pulse Sequence

Field of View, cm

Slice Thickness, mm

Matrix

Repetition Time/Time to Echo

14 14 12–14 12–14 12–14

3 3 3 3 3

256 192 256 192 256 192 256 192 256 192

500–700/12–14 >4000/54 400–750/10–11 >3500/47 >3500/47–52

Coronal T1 Coronal T2 Axial T1 Axial T2 FS Sagittal T2 FS

The MCL is best assessed on coronal and axial T2-weighted sequences with fat saturation. The anterior band is normally a homogenous hypointense structure that is flared in its proximal portion at the medial epicondyle and tapers distally. Mild linear high signal may be seen in the proximal portion deep to the humeral attachment and is caused by the normal invagination of the joint synovium and should not be interpreted as abnormal. The distal insertion on the olecranon has a very discrete tight-appearing osseous attachment. Thickening of the insertion greater than 3 mm should raise the suspicion of an undersurface tear.6 Partial-thickness tears appear as focal partial discontinuity of the fibers or focal intracapsular extension of joint fluid. In throwing athletes, partial tears most commonly occur in the deep undersurface fibers of the anterior bundle at the distal insertion site on the sublime tubercle and manifest as a partial-thickness avulsion of the deep fibers. A detached bone fragment in continuity with the MCL can typically be seen. Diagnosis with routine MRI can be difficult and magnetic resonance arthrography can increase the conspicuity of the tear. A small focus of fluid between the distal deep fibers of the MCL and the coronoid tubercle is specific for a partial-thickness tear and has been called the T sign.7,8 Complete tears of the MCL most commonly occur in the midsubstance of the MCL. Magnetic resonance shows a fluidfilled gap extending through the ligament and ligament laxity. The torn fragments of the ligament may also be seen. In the acute setting, there is often a joint effusion, periligamentous edema and strain of the overlying common flexor tendon origin (Fig. 2). Magnetic resonance imaging had a reported sensitivity and specificity of 100% for diagnosis of complete UCL tears, but only 14% sensitivity and 100% specificity for diagnosis of partial tears.7 Chronic ligament injury is characterized by absence of the edema

and effusions with thickening and scarring of the ligament, and occasionally, foci of calcification or heterotopic bone is seen.9 Operative management of an MCL injury is indicated if there is severe valgus instability due to a complete tear of the MCL and CFO. High-level throwing athletes with an acute complete tear and patients who have ongoing symptoms despite rehabilitation are further indications. The most common surgery for an MCL injury is harvesting a free tendon graft from either the semitendinosus or the palmaris longus. Osseous tunnels are created in the humerus and ulna, and the graft is orientated in a similar plane to the MCL. The surgery is now referred to as the “Tommy John surgery,” made famous by Dr Frank Jobe,10 who performed it on a former major league baseball pitcher, Tommy John, in 1974. He went on to win 164 games after the procedure.

FIGURE 1. Coronal PD sequence with fat saturation illustrating the normal anatomy of the MCL with its origin at the medial epicondyle (ME) of the humerus and distal insertion on the coronoid process of the ulnar (U).

FIGURE 2. Coronal PD sequence with fat saturation demonstrating an acute complete tear of the MCL from its proximal insertion on the ME with distal retraction (arrow). Edema within the surrounding soft tissues (asterix).

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Medial Epicondylitis Medial epicondylitis or “golfer’s elbow” (or “medial tennis elbow”) is most typically seen in athletes who are repetitively stressing the flexor pronator mass in addition to excessive valgus force. Golfers and athletes involved in overhead throwing such as tennis, racquetball, squash, and javelin throwing are most commonly implicated.11 The flexor carpi radialis and the pronator teres are the most commonly involved sites for the development of medial epicondylitis.12 Persistent tension and stress at the CFO cause microtearing, which in turn results in disorganized, immature collagen formation with immature fibroblastic and vascular elements.13 The range of pathology varies from tendinosis to partialand full-thickness tears of the common flexor tendon. In most cases, conservative management with rest, icing, bracing, physical therapy, or injections is successful. Surgical intervention is reserved for chronic refractory cases, and unlike the arthroscopic

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techniques used in the treatment of lateral epicondylitis, surgical reports of medial epicondylitis have been limited to open and percutaneous procedures because of the proximity to the ulnar nerve. Removal of the abnormal portion of the tendon the normal healthy tendon is reattached or repaired. The normal CFO is seen as homogenous low-signal-intensity structures on both T1- and T2-weighted images originating from the medial epicondyle. The CFO is best evaluated on coronal and axial images. In tendinosis, thickening and intrinsic intermediate signal change is demonstrated often in conjunction with edema in the adjacent soft tissues (Figs. 3A, B). Partial-thickness tears often manifest as diminution or attenuation of the tendon with intrasubstance linear high-signal change. If a partial tear occurs at the CFO attachment, an associated avulsion and retraction of the tendon may be seen. Full-thickness tears are identified as complete discontinuity of the CFO fibers with mild retraction, fluid in the region of the tear, and often edema in the adjacent soft tissues.

Posteromedial Impingement Posteromedial impingement or valgus extension overload is most commonly seen in throwing athletes,11 especially baseball pitchers and is due to repetitive excessive valgus forces during the early acceleration phase of the throwing cycle.12 The mechanism of injury is secondary to medial joint distraction, lateral joint compression, and rotatory forces at the olecranon.13 Repetitive microtrauma of the anterior MCL occurs and results in attenuation of the ligament. Consequently, abnormal valgus rotation of the elbow affects the mechanics of the posterior elbow joint, and bony impingement in the posteromedial compartment occurs. Chronic impingement and increased shear forces on the olecranon result in posteromedial olecranon osteophyte formation causing pain and decreased range of motion during flexion. The osteophytes may occasionally fracture forming intra-articular loose bodies.11 Injury and valgus laxity of the MCL may place increased stress on the adjacent medial tendons and soft tissues resulting in common flexor tendinosis and ulnar neuropathy.14,15 Compression on the lateral compartment may produce osteochondral injuries and early osteoarthritis of the radiocapitellar joint.12

Little Leaguer’s Elbow In school-aged athletes, the incidence of baseball-related overuse injuries is 2% to 8% with a 20% to 40% incidence of

Elbow MRI: Imaging Anatomy and Evaluation

elbow pain in baseball players aged 9 to 12 years.16 In 1960, Brogdon and Crow described 2 cases of separation and fragmentation of the medial epicondylar apophysis in the elbows of little league pitchers and coined the term “little leaguer's elbow.”14,15 Over time, it has been associated with several other injuries of the elbow such as osteochondritis dissecans (OCD) of the capitellum and trochlear and olecranon apophysitis.17 The medial epicondyle is 1 of the first apophyses to ossify at 6 years old, but the last ossification center to fuse with the distal humerus in the mid to late teens.18 The classic “little leaguer’s elbow” is a medial epicondyle apophysitis and is most commonly seen in baseball pitchers younger than 10 years.19,20 The initial radiographic findings are normal in the majority of patients with manifestations of displacement and fragmentation of the medial epicondyle apophysis seen later in the injury.19–21 Repetitive chronic traction on the medial epicondyle apophysis can result in bony overgrowth and overlying soft tissue swelling.22 Magnetic resonance imaging is useful for evaluation of the medial epicondyle apophysis and the physis, particularly when the initial radiograph is normal. Coronal images best depict the abnormality. Manifestations include widening, irregularity, and T2 hyperintensity of the physis between the distal humerus and medial epicondyle. Bone marrow edema and fragmentation of the apophysis may also occur. The CFO can also be affected, manifesting as thickening and high signal on both T1 and T2 sequences.22 Conservative management is indicated in the majority of patients. Surgical intervention is reserved for those where there is greater than 5-mm separation of fragments, instability, or incarcerated fragments.

Osteochondral Lesions of the Capitellum Injury to the articular surface of the joint is most common on the radial aspect where the convex surface of the capitellum is most vulnerable.21–23 The most common osteochondral lesions affecting the capitellum are Panner disease and OCD. The term osteochondrosis encompasses both entities. Panner disease is similar to Legg-Calvé-Perthes disease of the proximal femoral epiphysis and attributed to avascular necrosis of the capitellum. The dominant elbow in boys between the ages of 5 and 12 years is most commonly affected.22 The initial radiographic appearances can be subtle, most frequently manifesting as radiolucency with surrounding sclerosis at the

FIGURE 3. Coronal PD (A) and axial PD (B) sequences with fat saturation showing thickening of the proximal CFO at the ME of the humerus (ME) with surrounding edema (arrow). © 2015 Wolters Kluwer Health, Inc. All rights reserved.


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articular surface of the capitellum. As it progresses, larger areas of lucency coexisting with diffuse sclerotic changes are seen, and fragmentation may occur.24,25 Typically, MRI demonstrates diffuse capitellar edema but no morphological changes.26 With conservative management and limitation of activity, there is excellent recovery and long-term prognosis.24 Resolution of the MRI and radiographic abnormalities typically occurs after 1 to 2 years and lags behind the improvement in clinical symptoms.25 Osteochondritis dissecans of the capitellum typically occurs in older adolescents between the ages of 11 and 15 years. Unlike Panner disease, it is believed to be caused by repetitive microtrauma to the radiocapitellar joint and limited healing due to its weak blood supply.26 The entire capitellum receives its blood supply from 1 or 2 small blood vessels that enter posteriorly and extend through all of the capitellar cartilage. No collateral flow exists, thereby limiting healing of the capitellum after repetitive trauma.26 The condition is most commonly reported in young baseball players where the late cocking phase of the throwing cycle produces compressive forces on the lateral elbow. Young gymnasts may also be affected, and the mechanism of injury is due to compressive, shearing forces across the radiocapitellar joint.27 As with Panner disease, the initial radiographic appearances may be subtle. Magnetic resonance imaging depicts a range of abnormalities including abnormal bone marrow signal, cartilage defects, subchondral cystic change, fragmentation, and intra-articular loose bodies.28,29 Typically, an intermediate- to low-signal subchondral lesion on T1-weighted sequences with or without involvement of the overlying cartilage is seen28,29 (Figs. 4A–D). Magnetic resonance imaging arthrography can improve staging of the OCD. Unstable lesions are characterized by contrast surrounding the bony fragment or cystic change seen adjacent to the lesion.22 The bony fragment may displace from the humerus into the elbow joint. Treatment of the OCD depends on the extent of fracture displacement. Conservative management is indicated if there is no displacement with cessation of activity, rest, and gradual return to gentle exercise. Surgical management is used if there is failure of conservative management, an unstable fragment, or an intraarticular loose body. Procedures vary from fixation of the bony fragment, fragment removal, drilling of the lesion or the residual defect, and reconstruction with osteochondral autograft.30–32

LATERAL COMPARTMENT Anatomy The lateral aspect of the elbow joint is centered on the radiocapitellar joint, stabilized by the lateral (or radial) collateral ligamentous complex, and surrounded by the joint capsule. The lateral compartment contains the extensor muscles of the wrist and the supinator. The radiocapitellar joint laterally, together with the radioulnar joint, allows flexion and extension at the elbow as well as pronation and supination of the forearm. The lateral ligamentous complex of the elbow consists of 3 components, the radial collateral ligament (RCL), the lateral ulnar collateral ligament (LUCL), and the annular ligament. The RCL of the elbow (Fig. 5) originates from the anterior margin of the lateral epicondyle with a fan-shaped insertion distally into the annular ligament of the radius and the fascia of the supinator muscle. The RCL provides varus stability to the elbow joint.14,15 The annular ligament is wrapped around the radial head without attaching to it with anterior and posterior attachments at the anterior and posterior aspects of the lesser sigmoid notch on the ulna.17 The annular ligament is the primary stabilizer of the proximal radioulnar joint. The primary constraint of the elbow against posterolateral rotational instability (PLRI) is the LUCL. The LUCL is part of the lateral capsuloligamentous complex; at its origin at the lateral epicondyle, it is indistinguishable from the RCL, and it courses around the dorsal aspect of the radial head, posterior to the annular ligament where some fibers may blend with the annular ligament, inserting on the supinator crest of the posteromedial aspect of the proximal ulna (Fig. 6). Because of the oblique course of the LUCL, it can be difficult to image; however, it is usually best demonstrated on coronal images with axial and sagittal images useful to confirm suspected pathologies. The ligaments are normally uniformly low signal on all sequences; cadaveric studies have suggested that intermediate-weighted imaging with high spatial resolution and magnetic resonance arthrography were best suited to the diagnosis of LUCL tears.16 The common extensor origin (CEO) originates at the lateral epicondyle (Fig. 5). This conjoint tendon gives rise to, from medial to lateral, the extensor carpi ulnaris, extensor digiti minimi,

FIGURE 4. A, Coronal T1-weighted sequence demonstrating an ovoid lesion in the capitellum with a central area of intermediate signal intensity and a linear hypointense surrounding ring. B, Sagittal T1-weighted sequence again demonstrating the osteochondral lesion. C, Sagittal PD sequence showing the osteochondral lesion with deficiency of the overlying cartilage. D, Sagittal GRE sequence showing a displaced intra-articular fragment of cartilage.

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overload syndrome, occult fractures, and arthritis,21 and to assess cases of recalcitrant epicondylitis especially with poor response to treatment. Pathologically, lateral epicondylitis almost always involves the ECRB tendon with involvement of extensor digitorum communis in a further one-third of all patients21–23; however, on MRI, signal alternation most commonly affects the whole mass of the CEO.24 In the early stages of disease, edema of the CEO is the most consistent finding24 and together with intrasubstance tears is in keeping with CEO tendinosis. Edema presents with thickening and increased intratendon signal intensity of the CEO (Figs. 7A, B), whereas intratendon signal intensity similar to fluid, as in other tendons in the body, represents intrasubstance partialthickness tears. Other findings included peritendon edema and signal changes in the lateral epicondyle representing focal bone edema. Less commonly, there may be a radial bursitis and changes in the anconeus muscle or within the subjacent RCL. The LUCL must be carefully assessed as lateral epicondylitis has been shown to be associated with thickening and tears of the LUCL.25

FIGURE 5. Normal RCL and CEO. T2-weighted imaging demonstrates the RCL (solid arrow) is seen deep to the CEO with its proximal insertion at the anterior margin of the lateral epicondyle with a fan-shaped insertion distally into the annular ligament of the radius(R).

extensor digitorum, and extensor carpi radialis longus and extensor carpi radialis brevis (ECRB). The supinator has a broad-based origin from the lateral epicondyle, the lateral collateral ligament of the elbow, the annular ligament, and the supinator crest of the ulna and an oblique insertion on the lateral anterior surface of the upper third of the radius covering the upper third of the radius. The orientation of the CEO is parallel to the lateral or RCL and is therefore also best visualized on the coronal images and should be uniformly low signal. The CEO should also be assessed on the axial images, in particular regarding thickening of the tendon, similar to the collateral ligaments at the knee. Variant soft tissue anatomy includes the accessory lateral collateral ligament and congenital absence of the LUCL.18 The accessory lateral collateral ligament can be present in up to onethird of people, running from the annular ligament to the supinator crest, and acts to reinforce the annular ligament. A common osseous variant not to be confused with a pathological process includes the pseudodefect of the capitellum.19,20

Trauma Disruption of the lateral collateral ligament complex can result in PLRI; tears of the LUCL in particular predispose to this as the LUCL, which is the primary constraint of the elbow joint against PLRI. Lateral collateral ligament complex tears are best visualized in the coronal plane on magnetic resonance images. Injury of the RCL is less common than that of the MCL; the RCL is usually injured on a fall on an outstretched hand with the forearm supinated or during elbow dislocation. Disruption of the RCL can also occur during elbow dislocation or against a background of lateral epicondylosis. Ligamentous avulsions from the humeral origin (Fig. 8) are most common in this setting, followed by midsubstance rupture; tears from the radial insertion are rare.26 Magnetic resonance appearances of RCL injuries

Lateral Epicondylitis Lateral epicondylitis, often referred to as tennis elbow, is a common condition and together with medial epicondylitis is the most common cause of discomfort at the elbow. It is most often the result of repetitive stress injury. This results in microtears within the CEO and subsequent degeneration, immature repair with neovascularity, and tendinosis. The extensor carpi radialis brevis tendon in particular is in direct contact with the capitellum placing it at increased risk for repeated undersurface abrasion during elbow extension. Clinically, patients present with focal pain and tenderness at the CEO, and the diagnosis is usually made on clinical examination. Diagnostic imaging may be used with atypical presentations, to exclude differential diagnoses, which include nerve entrapment syndromes, posterolateral rotatory instability, posterolateral plica syndrome, Panner disease (typically in younger children aged 5-12 years, usually dominant elbow), OCD of the capitellum (occurs in the older child or adolescent), radiocapitellar

FIGURE 6. Normal LUCL. Coronal oblique, T1-weighted image through the posterior aspect of the elbow demonstrates the LUCL (arrowheads), which originates at the lateral epicondyle, deep to the CEO (short arrow), passes posterior to the radial head (R), and attaches distally on the supinator crest (dashed arrow) of the posteromedial ulna.



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FIGURE 7. Lateral epicondylitis. Axial (A) and coronal (B) proton density (intermediate-weighted) images with fat saturation reveal signal hyperintensity with the CEO consistent with epicondylitis. There is subtle marrow edema in adjacent lateral epicondyle (LE). Radial head (R).

include thickening of the ligament, signal hyperintensity consistent with edema, foci of hemorrhage in the acute phase (best appreciated on gradient echo sequences), and discontinuity of the ligament. Tears of the ligament can be partial or full thickness and present with increased signal intensity on fat-saturated proton density, T2-weighted, and short tau inversion recovery sequences. Injury to the LUCL may occur on acute varus extension, during elbow dislocation, or as a complication of lateral epicondylitis. The LUCL may also be disrupted during overaggressive release of the CEO in lateral epicondylitis treatment or during resection of the radial head. Tears of the LUCL occur most commonly at the humeral origin, at the common attachment with the RCL. The LUCL is best assessed on oblique coronal images where the oblique coronal plane is parallel to a line drawn between the humeral epicondyles.16 On MRI, there is signal hyperintensity with disruption of the ligament, which normally returns low signal. However, accurate assessment of the LUCL can be difficult because of its oblique course, and even the intact LUCL is rarely seen as a distinct low-signal band; the LUCL can generate artifact that can be confused with ligament rupture.27 Secondary supporting evidence can be used that includes inability to achieve full extension because of apprehension and posterior subluxation of the radial head relative to the capitellum consistent with PLRI, best appreciated in the sagittal plane.28,29 Magnetic resonance arthrography greatly improves the conspicuity of LUCL tears with hyperintense contrast disruption of the low-signal ligament.16

estimated area of 3 mm2.34 The superficial short head inserts more distally and anteriorly on the radial tuberosity contributing on average 12 mm to the total footprint, allowing for increased flexion power than the long head, which contributes the remainder of the footprint and inserts more proximally, farthest from the axis of rotation of the radius and thus providing a greater lever arm for supination.35 Partial or complete separation of both heads all the way to the distal insertion is common, seen in up to 40% (Fig. 9). There is no tendon sheath surrounding the distal tendon; rather, it is covered in an extrasynovial paratenon. The bicipitoradial bursa lies interposed between the distal tendon and the radial tuberosity, facilitating smooth motion in elbow flexion and supination. A

ANTERIOR COMPARTMENT Anatomy The brachialis and biceps brachii comprise the tendons of the anterior compartment and are the main flexors of the elbow. The brachialis muscle originates along the distal aspect of the anterior humeral shaft and extends along the anterior elbow joint capsule. Distally, it forms a short thick tendon and inserts on the ulnar tuberosity. The biceps muscle lies superficial to the brachialis in the arm. It has 2 heads, the long head that originates at the supraglenoid tubercle and superior labrum, and the short head originating at the coracoid process of the scapula. Supernumerary heads have been described in between 9% and 21% of the population in cadaveric studies,30–32 most commonly arising from the humeral shaft. The tendon footprint inserts distally onto the radial tuberosity with an average footprint length of 21 mm33 and an

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FIGURE 8. Radial collateral ligament tear. Coronal PD intermediate-weighted images with fat saturation in a patient following trauma to the elbow. There are ligamentous avulsions of the RCL from its humeral origin. There is associated edema in the lateral epicondyle. The CEO remains intact. © 2015 Wolters Kluwer Health, Inc. All rights reserved.




FIGURE 11. The “hook test” is a clinical test to assess for rupture of the distal biceps tendon.

FIGURE 9. Axial PD magnetic resonance image with fat saturation of the elbow demonstrating a bifid biceps tendon (arrow).

separate adjacent bursa, the interosseous bursa, lies medially and abuts the interosseous membrane. Neither of these is visible on imaging in the normal state. The biceps is at least in part kept in position by the lacertus fibrosis (or bicipital aponeurosis), a thin fibrous band that connects the short head of the biceps tendon medially with the deep fascia of the forearm overlying the flexor compartment. When intact, this can prevent proximal retraction of the biceps in the setting of tendon disruption (Fig. 10).

Distal Biceps Rupture of the distal biceps tendon represents only 3% of all biceps ruptures33,36 with a reported incidence of 1.2 per 100,000 people. Rupture most typically occurs in men with an average age of 50 years, the dominant arm affected in the majority of cases. The reported risk factors include male sex, anabolic steroid use, body building, and smoking.37–39 Most injuries occur during heavy lifting, resulting from a sudden, forceful contraction

FIGURE 10. Normal anatomy of radial nerve (RN), ulnar nerve (UN), and median nerve (MN). T1-weighted axial plane. Normal anatomy of the elbow at the level of the radial head (R). The lacertus fibrosis (LF) is best seen on T1-weighted axial image without fat saturation. The rim of fat enables visualization of the UN and the RN. The nerves are isointense to muscle and difficult to visualize without a rim of fat as in the case of the MN.

or prolonged overload of the biceps tendon with the elbow in midflexion. The vast majority of the tears are complete; however, partial tears have also been described,40–45 as well as isolated tears of 1 of the 2 tendons in the setting of a bifid tendon,46 which may be more common than previously thought. Partial tears are often associated with bicipitoradial bursitis. The typical history is a male patient presenting with a sudden episode of severe pain during forced eccentric contraction of the biceps. A popping or snapping sensation is often felt followed by marked diminution of strength, particularly elbow flexion and supination. Ecchymosis on the medial aspect of the elbow is often seen. Proximal migration of the tendon with a complete tear results in absence of the biceps from the antecubital fossa and prominence of the anteromedial aspect of the forearm, the so-called “Popeye deformity.” The “hook test” is used clinically to assess integrity of the distal biceps (Fig. 11). The degree of retraction can depend on the integrity of the lacertus fibrosis. If it remains intact, there may be little or no retraction of the biceps tendon, which can make clinical diagnosis difficult. When imaging with MRI, it is important that axial images extend from the musculotendinous junction to the distal insertion on the radial tuberosity. Axial images are useful for assessing the extent of disruption distally (Fig. 12), and sagittal images are best suited for demonstrating the degree of musculotendinous retraction (Fig. 13). The flexed abducted supinated view (Fig. 14) has been shown to be of use in evaluating the distal biceps.1,47 This involves imaging the flexed elbow with the shoulder abducted

FIGURE 12. Axial PD sequence with fat saturation of the elbow showing absence of and extensive edema in the line of the biceps tendon. This was a complete rupture of the distal biceps tendon with retraction.



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FIGURE 13. Sagittal GRE sequence of the elbow in the same patient as Figure 4 demonstrating complete rupture of the distal biceps tendon with retraction (arrow). Extensive edema in the expected course of the tendon (asterix).

and the forearm in supination view. Magnetic resonance imaging findings of partial tears include either focal or diffuse changes in signal intensity and caliber of the tendon. A complete tear of the tendon results in a gap between the proximal and distal aspects with variable degrees of retraction depending on the involvement of the lacertus fibrosis. An intact lacertus fibrosis results in a

FIGURE 15. Flexed abducted supinated T2-weighted sequence demonstrating a complete rupture of the distal biceps tendon, which is retracted (broken arrow) from its insertion on the radial tuberosity (arrow) with edema in the soft tissues (asterisk).

complete tear or avulsion distally with little or no retraction. On the other hand, a tear in the lacertus fibrosis demonstrates thickening and edema in the aponeurosis and significant proximal retraction (Fig. 15). The size of the gap is important to comment on for operative planning. Tendinosis is most often seen with repetitive activities such as weight lifting and commonly results in focal or diffuse thickening and alteration in signal within the tendon.

Brachialis Isolated injuries of the brachialis tendon are rare48 and most commonly occur with posterior or posterolateral dislocation of the elbow.34 A mild (grade 1) muscle strain may occur occasionally in the distal brachialis tendon when the distal biceps tendon is torn.

Bursitis Bursitis typically presents with pain, occasionally restriction of motion, and a well-defined cystic mass in the location of either of the 2 previously described bursae, the bicipitoradial and/ or interosseous bursae.49 Bursitis is most often due to repeated mechanical trauma50; however, inflammatory arthropathy,51 infection, chemical synovitis,52 synovial chondromatosis,53 and lipoma arborescens54,55 have all been described.

POSTERIOR COMPARTMENT Anatomy FIGURE 14. Flexed abducted supinated T2-weighted sequence showing a normal distal biceps tendon as it courses to its insertion on the radial tuberosity (arrow).

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The posterior compartment of the elbow contains the elbow extensors. The triceps brachii muscle is the major extensor of the elbow. It is a tripennate muscle: the long head has its origin © 2015 Wolters Kluwer Health, Inc. All rights reserved.




FIGURE 16. Triceps avulsion. A small avulsed fragment of the olecranon on the lateral plain film of the elbow (A). The avulsed fragment (*) can be subtle on MRI. The triceps tendon (TrT) has been avulsed with a small fragment of bone (*) from the olecranon (U). Soft tissue edema and bone edema of the olecranon (U) are demonstrated on the sagittal T2-weighted magnetic resonance images with fat suppression (B). The lateral aponeurotic extension of the triceps (C) (straight arrow) blends with the anconeus and proximal forearm fascia. This typically remains intact despite a full-thickness biceps tendon tear.

at the infraglenoid tubercle of the scapula, the lateral head originates at the upper posterior humerus, and the medial head has a broad-based origin at the lower posterior humerus. On MRI images, it can appear to have a bipartite insertion at the olecranon, with a deep medial head that has a very distal myotendinous junction; however, the triceps tendon inserts as a single unit on the olecranon56 with a further small lateral aponeurotic extension57 that extends over the anconeus muscle to blend with the anconeus and proximal forearm fascia (antebrachial fascia) (Fig. 16C). There is normal interposition of fat between the fascicles of the distal triceps tendon, giving it a striated appearance (Fig. 17), and this should not be misinterpreted as tendinosis.

FIGURE 17. Triceps tendon striated. Coronal T1-weighted magnetic resonance image demonstrating the normal striated appearance of the distal TrT (solid arrow) at its insertion on the olecranon (U).

At the posterolateral aspect of the elbow, the anconeus muscle originates at the lateral epicondyle posteriorly and inserts on the radial surface of the olecranon. The anconeus epitrochlearis (Fig. 18) is an anomalous muscle, which originates at the ulna aspect of the olecranon and inserts on the medial epicondyle of the humerus; the belly of the muscle lies posterior to the ulna nerve, and the muscle can vary in size. This muscle can have a prevalence of up to 34% and if present is more commonly bilateral.58 The anconeus epitrochlearis lies within the cubital tunnel and has been associated with ulnar nerve compression syndromes. A common joint capsule surrounds the elbow, having a fibrous outer layer and a deep synovial layer. The fat pads of the elbow are situated between these 2 layers. The posterior fat pad lies within the olecranon fossa. The superficial olecranon bursa overlies the dorsal bony prominence of the olecranon and deep

FIGURE 18. Anconeus epitrochlearis (AE) muscle is seen superficial to the UN on T1-weighted axial MRI. The muscle replaces the fat normally seen deep to the cubital tunnel retinaculum (Osborne ligament). The muscle takes the same course as Osborne ligament, running from the medial cortex of the olecranon to the inferior surface of the ME. Often, however, the proximal insertion of the RCL cannot be differentiated separate from the CEO.



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FIGURE 19. Triceps partial tear sagittal and axial. Sagittal (A) and axial (B) T1-weighted magnetic resonance image demonstrating a partial-thickness tear of the distal TrT. The deep, medial head (dashed arrow) remains intact, and the superficial conjoined lateral and longitudinal heads (solid arrow) have torn and are partially retracted. Olecranon of the ulna (U).

to the overlying skin and allows the elbow to flex and extend freely under the skin.

POSTERIOR ELBOW TRAUMA Triceps Distal triceps tendon tears are relatively rare with a prevalence of 1% to 3.8%59; however, they are increasingly being diagnosed on MRI, in particular partial-thickness tears that are more common than complete tears (Figs. 19A, B) and avulsions (Figs. 16A–C). Triceps tendon tears most commonly occur following sports injuries where eccentric loading of a contracting triceps has been implicated. They are also often the result a fall on an outstretched hand or a direct blow. Local and systemic risk factors include local steroid injection, olecranon bursitis, and hyperparathyroidism. Magnetic resonance imaging can distinguish between partial- and full-thickness tears.17 A complete rupture is usually associated with extensive adjacent soft tissue edema and retracted tendon margins on the sagittal images (Figs. 20A–C). The lateral

head insertion, which is contiguous with the anconeus muscle, is invariably intact even in the setting of a complete rupture (Fig. 16C). Axial and sagittal magnetic resonance images are useful for evaluating the triceps tendon and the degree of retraction. Axial images can be helpful to localize the components and the extent of the tendon involved, whereas coronal images are used to determine if a tear is complete or partial.60 Olecranon bursitis (Fig. 21) may mimic or accompany triceps tendon tears and can account for significant associated soft tissue edema. On MRI, tendinosis and tendon strain tend to obscure the distinction of the individual muscle fibers and often present with thickening and increased heterogeneous intrasubstance signal intensity of the distal tendon.

Olecranon Stress Fractures Marrow-sensitive sequences with MRI are very useful in diagnosing and assessing radiographic occult fractures. In the elbow, this is of particular importance with olecranon stress fractures. Fat-suppressed T2-weighted images are the most sensitive in assessing for a potential stress or occult fractures and associated

FIGURE 20. Triceps full tear sagittal (A), axial proximal (B), and distal (C). Full-thickness tear (*) of the TrT at the myotendinous junction on Sagittal T2-weighted magnetic resonance image with fat suppression of the elbow in an adult patient. There is no bone edema of the olecranon (U). The proximal portion (T) of the TrT is retracted, and the distal portion (TrT) is lax. The proximal retracted tendons (T) and the absent tendon (*) at the level of the tear can be seen on proximal (B) and distal (C) axial images, respectively. Humerus (H).

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FIGURE 21. Olecranon bursitis. Sagittal PD intermediate-weighted fat-suppressed of right elbow reveals effusion in the olecranon bursa (OB) with marked hyperintense signal of the collection with some heterogeneity consistent with a degree of synovial hypertrophy. Extensive surrounding soft tissue edema. Ulnar (U) and humerus (H)

marrow edema; however, it is important to correlate on T1-weighted images, which are more specific. Fractures demonstrate a linear pattern both on the T1- and T2-weighted images. These fractures commonly occur in throwing athletes as a result of repetitive microtrauma caused by olecranon impingement or excessive triceps tensile stress. Magnetic resonance imaging can depict abnormalities weeks before radiographic changes and has a comparable sensitivity and greater specificity to bone scintigraphy.61,62 Magnetic resonance imaging can detail associated injuries to surrounding musculoligamentous components and is also useful in the follow-up of healing stress fractures with resolution of abnormal increased signal intensity on fluid-sensitive sequences within 6 months of the first imaging study in about 90% of cases. In children and adolescents, the fracture most commonly occurs at the physeal plate. The classic olecranon stress fracture in the skeletally mature patient is an oblique fracture. On a direct anteroposterior (or coronal) view, the fracture line extends from the proximal-ulnar side toward the distal-radial side; on the lateral or sagittal view, the fracture extends from the olecranon articular surface toward the proximally and dorsally.63 Stress fractures of the extreme tip of the olecranon is thought to be due to impingement of the olecranon tip against the fossa in terminal extension of the elbow; this has been reported in javelin throwers, and a displaced fragment may even be seen on radiographs.64

NERVES ANATOMY AND PATHOLOGY Radial Nerve Anatomy The radial nerve is composed of C5-T1 nerve roots from the posterior cord of the brachial plexus. The radial nerve contours


along the spiral groove of the midshaft of the humerus from the posterior to the anterior compartment of the arm as it penetrates the lateral intermuscular septum approximately 10 to 12 cm proximal to the elbow.65 The nerve then passes through the radial tunnel at the lateral aspect of the anterior compartment. The radial tunnel is a potential space, extending approximately 5 cm along the anterior aspect of the proximal radius from the radiocapitellar joint to its inferior border at the distal margin of the supinator muscle. The radial recurrent vessels, the superficial head of supinator, and brachioradialis form the roof. The biceps and brachialis tendon form the medial wall of the tunnel; the lateral margin comprises the extensor carpi radialis longus and brevis. The capsule of the elbow joint forms the floor of the tunnel. Within the tunnel, the radial nerve divides into the radial sensory nerve (RSN) and the deep posterior interosseous nerve (PIN).66 The PIN runs between the deep and superficial parts of the supinator muscle to enter the posterior compartment of the forearm and then courses distally along the dorsal aspect of the interosseous membrane. The most superior part of the superficial supinator muscle forms a fibrous arch, the arcade of Frohse. The arcade of Frohse is a tendinous structure in the majority of cases and is the most common site for PIN entrapment at the elbow.67 The RSN follows the radial artery distally and dorsal aspect of the thumb as well as the index finger and middle finger. On MRI, the radial nerve is best demonstrated on the axial sequences, in particular at the superior aspect of the elbow (Fig. 10), within the fat between brachioradialis and brachialis muscles.2 The bifurcation of the radial nerve may be seen at the level of the radiocapitellar joint. The PIN can be identified between the deep and superficial portions of the supinator muscle. The signal characteristics are similar to those of the median and ulnar nerves: low signal on the T1-weighted images and isointense to muscle on the T2-weighted images. The arcade of Frohse can be identified on MRI as a low-signal band at the proximal aspect of the supinator muscle.68

Radial Nerve Entrapment The radial nerve can be compressed at a number of locations around the elbow, most commonly within the radial tunnel, and will then usually present with distinct clinical entities when it compresses the RSN or PIN individually.69 Sites prone to radial nerve compression around the elbow include fibrous bands around the radiocapitellar joint, the leash of Henry (recurrent radial artery vessels), ECRB, and the arcade of Frohse. Compressive factors that can cause radial nerve neuropathy, similar to all peripheral entrapment neuropathies, include soft tissue and bone tumors, synovitis and arthritis, ganglion cysts, gout, and vascular malformations. Radial tunnel syndrome can occasionally be caused by overuse (eg, in athletes) or external compression (eg, use of crutches). Radial tunnel syndrome is also referred to as PIN syndrome or supinator syndrome. The syndrome can present with 2 different clinical entities: with forearm pain but no weakness and alternatively with painless muscle weakness. Magnetic resonance imaging of the radial nerve often yields very little; occasionally, the compressed PIN may demonstrate highto intermediate-signal intensity on T2-weighted fat-suppressed or short tau inversion recovery images. The diagnosis of PIN syndrome is based primarily on the muscle denervation pattern, which may indicate the level of the nerve lesion.68 Up to half of patients demonstrate denervation edema or atrophy within the supinator muscle or the extensor muscles innervated by the PIN.70 Other findings include thickened leading edge of the extensor carpi radialis brevis and prominent radial recurrent vessels.



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A substantial number of patients have normal magnetic resonance findings.

Median Nerve Anatomy The median arises from the lateral cords of the brachial plexus (C6-T1). It courses adjacent to the brachial artery in the anterior compartment of the arm. The nerve has a superficial location as it courses through the antecubital fossa, lying posterior to the lacertus fibrosis (bicipital aponeurosis) and anterior to the brachialis muscle. At the elbow joint, the median nerve lies between the humeral (superficial) and ulnar (deep) heads of the pronator teres muscle. It supplies the pronator teres, flexor carpi radialis, palmaris longus, and flexor digitorum superficialis muscles. Close to the bifurcation of the brachial artery, the anterior interosseous nerve arises from the median nerve and travels along the anterior aspect of the interosseous membrane of the forearm to the wrist.

Median Nerve Entrapment Pronator syndrome results from entrapment of the median nerve around the elbow. Entrapment can occur at the distal humerus by the ligament of Struthers, the proximal elbow by a thickened biceps aponeurosis, at the elbow joint between the 2 heads of the pronator teres, and in the proximal forearm by a thickened proximal edge of the flexor digitorum superficialis muscle. The ligament of Struthers is a relatively rare cause of median nerve compression. It is a fibrous vestigial remnant present in 2.7% of the population extending from the anteromedial aspect of the distal humerus to the medial epicondyle.68,71,72 If a supracondylar spur is present, the ligament can originate here in approximately 1% of the population and result in median nerve compression.73 The most common cause of pronator syndrome is a result of dynamic compression of the nerve between the superficial humeral head and the deep ulnar heads of the pronator teres muscle with pronation. The bicipital aponeurosis (lacertus fibrosis) can become thickened and result in compression of the pronator muscle and the median nerve. Partial tendon tears, supracondylar spurs, and bicipital-radial bursitis can also cause irritation of the nerve. Compression of the median nerve can present in 2 ways: pronator syndrome and anterior interosseous nerve syndrome. Patients with pronator syndrome typically present with pain and paresthesia in the anterior elbow and forearm. Sports that entail repetitive forceful pronation and supination (eg, pitching, rowing, weight training, and racquet sports) can cause pronator syndrome.74 In the hand, the first to third digits and the lateral aspect of the ring finger are affected. The hand symptoms are similar to carpal tunnel syndrome, but pronator syndrome may have associated numbness in the palm because of involvement of the palmar cutaneous nerve. Unlike pronator syndrome, carpal tunnel symptoms are worse at night, and typically, there is a positive Tinel sign on examination. Anterior interosseous syndrome (AINS), or Kiloh-Nevin syndrome, is a rare neuropathy of the anterior interosseous nerve, a purely motor branch of the median nerve that arises from the median nerve approximately 2 to 5 cm distal to the medial epicondyle. The most common causes of AINS are compression neuropathy, resulting in weakness of the flexor pollicis longus, flexor digitorum profundus to the second and third digits, and the pronator quadratus muscle. Although uncommon, this form of nerve compression is most frequently seen in throwers as a result of cumulative injury, violent muscle contraction, or even

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overaggressive exercises of the forearm.75 Parsonage-Turner syndrome (acute brachial neuritis) is a nonmechanical cause of AINS that can affect the anterior interosseous nerve and cause symptoms of AINS after a transient period of shoulder pain.72,74,76 The median nerve is best evaluated on axial images with prone positioning of the arm. Although a tiny structure, this positioning allows for more fat to be present around the nerve. Magnetic resonance imaging can display direct causes of nerve compression such as ganglion cysts, nerve sheath tumors, and osseous spurs. Fluid-sensitive sequences can demonstrate hyperintense signal changes secondary to muscle denervation edema.77

Ulnar Nerve Anatomy The ulnar nerve is composed of C8 and T1 motor and sensory nerve fibers from the medial cord of the brachial plexus. The nerve demonstrates intermediate signal on the T1-weighted images and is slightly more hyperintense on the T2-weighted images where it is almost isointense to the adjacent muscle. Good visualization of the nerve is again dependent on a rim of surrounding fat. The nerve is usually best appreciated on axial images. The nerve passes from the anterior to the posterior compartment of the arm at the level of the midhumerus and can pass under the arcade of Struthers (not to be confused with Struthers ligament). The presence of the arcade of Struthers remains controversial, and its presence ranges from 13.5% to 100% of individuals78–81; when present, the arcade of Struthers is described as a thickening of the deep fascia of the distal arm that connects the medial intermuscular septum to the medial head of the triceps muscle, with the most proximal aspect located approximately 8 cm proximal to the medial epicondyle. At the level of the elbow, the ulnar nerve courses posterior to the medial epicondyle (Fig. 10), where it enters the cubital tunnel. The roof of the cubital tunnel is made up of the arcuate ligament or the cubital tunnel retinaculum, also known as Osborne band, which extends from the medial epicondyle to the medial olecranon process. The elbow capsule, the underlying ulna, and the medial band of the ulnar collateral ligament form the floor of the cubital tunnel. After exiting the cubital tunnel, the ulnar nerve provides motor branches to the flexor carpi ulnaris and the ulnar half of the flexor digitorum profundus. The ulnar nerve then passes between the 2 heads of flexor carpi ulnaris to reenter the anterior compartment of the forearm.

Ulnar Nerve Entrapment: Cubital Tunnel Syndrome Ulnar nerve entrapment can occur at a number of locations around the elbow including (1) at the medial intermuscular septum, (2) at the arcade of Struthers, (3) posterior to the medial epicondyle, (4) within the cubital tunnel, and (5) at the exit point of the flexor carpi ulnaris at the deep flexor pronator aponeurosis.82 The most common site of entrapment is within the cubital tunnel, this being the second most common site of upper-limb entrapment neuropathy—the most common being carpal tunnel syndrome of the median nerve at the wrist. Anatomy of the cubital tunnel can vary in individuals, and the volume of the tunnel varies in different positions of the elbow. The retinaculum is normally tightest in elbow flexion.83 Cubital tunnel syndrome is usually a clinical diagnosis that is confirmed with nerve conduction studies. Patients with ulnar nerve compression at any level have altered sensation in the little and ring fingers. It can be caused be ganglion cysts, synovitis, soft tissue tumors, nerve enlargement, and bony deformities. Nerve © 2015 Wolters Kluwer Health, Inc. All rights reserved.




FIGURE 22. Ulnar nerve neuritis (A) and flexor carpi ulnaris (FCU) atrophy (B). Hyperintense signal is seen within the UN at the level of the ME on T2-weighted imaging (A) with fat saturation, consistent with neuritis. This results in denervation and atrophy of the FCU muscle distal to the elbow, well demonstrated on the T1-weighted image (B).

enlargement can be cause by microtrauma, scarring, and edema. The nerve can further be compressed by edema within the surrounding soft tissue.84 Plain radiographs around the elbow may show osteoarthritis, calcification in the MCL, and remodeling deformities related to preexisting trauma. Magnetic resonance imaging is useful in showing lesions such as ganglions, neuromas, and synovitis. The nerve is well visualized on the axial images. Expansion of the nerve and abnormal increased T2 signal (Figs. 22A, B) within the nerve at the level of the cubital tunnel suggest cubital tunnel syndrome or neuritis.85 The changes in the nerve may be very subtle, and secondary supporting findings include denervation muscle atrophy and fatty infiltration (Fig. 22B). Magnetic resonance imaging may aid in diagnosing causative factors including thickening of the arcuate ligament, fluid-signal ganglion cysts, soft tissue masses, and inflammatory processes including olecranon bursitis. The normal variant anconeus epitrochlearis muscle must be identified as it can contribute to narrowing of the cubital tunnel. The nerve may lie outside the canal because of subluxation or postoperative transposition. If ulnar subluxation is suspected, additional images can be obtained with the elbow flexed; alternatively, dynamic ultrasound of the elbow may demonstrate the subluxing nerve.

INNOVATIONS IN ELBOW MRI IMAGING With its high spatial resolution, excellent soft tissue contrast, and multiplanar imaging capabilities, MRI is often the imaging modality of choice for the evaluation of the painful elbow. The major disadvantages of MRI are the long acquisition times and expense; however, the introduction of high-field scanners have reduced scan times and cost with improved image resolution. Now almost routine clinical MRI at field strengths of 3 T enables faster scan times, thereby increasing patient tolerance and potentially decreasing motion artifact. 3-T MRI has higher signal-to-noise ratio than lower-field MRI and hence improved spatial resolution with thinner slice profiles. Further adjuncts in MRI scanning of the elbow include magnetic resonance arthrography with the intraarticular injection of gadolinium or saline, which can be helpful when looking for subtle ligamentous injuries, osteochondral lesions, and intra-articular loose bodies.

Magnetic resonance neurography has been used at the elbow, in particular in assessing the ulnar nerve. It has been found to be diagnostically accurate for ulnar neuropathy using both increased cross-sectional size of the nerve and the ratio of signal of the ulnar nerve relative to that of normal muscle on T2-weighted imaging.86,87 The cross-sectional nerve size is more sensitive than signal change alone. A number of studies have looked at the use of diffusion tensor imaging in the evaluation of peripheral nerves; this may prove to be useful in proving information for the diagnosis and follow-up of nerve lesions, entrapments, and regeneration. Analysis of image data enables determination of fractional anisotropy and allows 3-dimensional visualization of the fiber tract, known as tractography.88,89 Diffusion tensor imaging and tractography remain largely research based but open the way to potential clinical applications as they propose to reveal abnormalities that are beyond the resolution of conventional magnetic resonance techniques.90 Novel MRI techniques have been developed more recently in order to improve articular cartilage assessment especially in joints with relatively thin articular cartilage, in particular the hip, elbow, and shoulder. This has involved surface evaluation and thickness measurements using cartilage specific sequences; however, consensus regarding examination technique has not yet been derived. The dGEMRIC (delayed gadolinium-enhanced MRI of cartilage) method of indirect (intravenous) magnetic resonance arthrography with delayed MRI and T1 relaxation mapping of the cartilage has been investigated in several in vitro and in vivo studies, performed in the knee initially91 and subsequently the hip92 to assess thinner articular cartilage. There has been little translation to the elbow joint, largely due to very limited treatment options available for early osteoarthritis of the elbow.

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