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Imaging 15:193-204 (2003)
© 2003 The British Institute of Radiology

Imaging of the elbow

J Teh, MRCP, FRCR1, V Sukumar, FRCR1 and S Jackson, MRCP, FRCR2

1 Department of Radiology, Nuffield Orthopaedic Centre NHS Trust, Windmill Road, Headington, Oxford OX3 7LD and 2 Department of Radiology, Salford Royal Hospitals NHS Trust, Stott Lane, Salford, Greater Manchester, M6 8HD, UK


   Summary
Top
 Summary
Imaging modalities
 Normal anatomy
 Disorders of the elbow
 Conclusion
 References
 

The elbow is a complex hinge-pivot joint with three components: the humeroradial, humeroulnar and radioulnar articulations. Flexion and extension occur at the humeroulnar articulation, whilst pronation and supination occur at the radioulnar articulation. The elbow is surrounded by numerous ligaments, tendons and muscles. The wide range of mechanical forces which act on this complicated joint makes it susceptible to a variety of injuries, which may be due to acute trauma or chronic overuse. This article will outline the pertinent anatomy and cover the common disorders which occur in the adult population.


   Imaging modalities
Top
 Summary
 Imaging modalities
Normal anatomy
 Disorders of the elbow
 Conclusion
 References
 
Plain radiography and CT are excellent for demonstrating osseous abnormalities and for detecting mineralization in or around the joint. Displacement of the fatpads may also be seen, which may indicate either effusion or synovitis (Figure 1Go). Ultrasound (US) is useful for demonstrating joint effusions or synovitis and loose intra-articular bodies. US also allows evaluation of the soft tissues, and may be useful for confirming the presence of chronic overuse injury such as epicondylitis or tendinopathy. MRI plays a key role in assessing the elbow in a variety of conditions, as it allows multiplanar evaluation of both the osseous and non-osseous structures. It is therefore well suited to detecting osteochondritis dissecans and loose bodies, as well as suspected ligamentous or tendon injury. MRI also has a major role in staging bone and soft tissue neoplasms. Bone scintigraphy, although extremely sensitive for detecting bony neoplasms and infection, is relatively non-specific and is therefore rarely used for diagnosing disorders of the elbow.



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  		Figure 1. Lateral radiograph of the elbow demonstrating elevation of the anterior (arrowheads) and posterior (black arrows) fat pads due to a radial head fracture (white arrow).

 

   Normal anatomy
Top
 Summary
 Imaging modalities
 Normal anatomy
Disorders of the elbow
 Conclusion
 References
 
The distal humerus consists of capitellum and trochlea. The unlar trochlear notch articulates with the trochlea. The posterior articular surface of the trochlear notch is derived from the olecranon process and the anterior portion arises from the coronoid process. The capitellum articulates with the head of the radius, which permits both flexion/extension and pronation/supination. The radial head articulates with a small depression along the lateral surface of the coronoid process, which permits rotation of the radius on the ulna [1, 2].

Joint stability is provided by the joint capsule and collateral ligaments. Adipose tissue lies between the synovial membrane and the joint capsule anteriorly and posteriorly.

The ulnar collateral ligament consists of three portions [2]. The anterior bundle consists of superficial and deep fibres and arises from medial epicondyle and inserts onto the coronoid. This portion acts as the major constraint to the valgus stress. The posterior bundle is a triangular fan-like ligament which also arises from the medial epicondyle and inserts into the medial olecranon margin. The transverse bundle extends between the coronoid process and olecranon and has little role in maintaining stability (Figure 2Go).



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  		Figure 2. Normal anatomy. Coronal T1 weighted image demonstrating the common flexor origin (arrowhead) and the ulnar collateral ligament (arrow) inserting onto the medial epicondyle.

 
The lateral collateral ligament complex is comprised of four separate parts [3]. The radial collateral ligament arises from the inferior aspect of the lateral epicondyle deep to the common extensor tendon. The lateral ulnar collateral ligament originates posteriorly and inserts onto the supinator crest of the ulna, acting as the major constraint to varus stress. The annular ligament encircles the radial head, attaching to the radial notch of the ulna. The accessory lateral collateral ligament is not always present.

There are four muscle compartments surrounding the elbow. The medial group of muscles is comprised of flexor carpi radialis and ulnaris, palmaris longus, flexor digitorum superficialis and pronator teres. They insert onto the medial epicondyle as the common flexor tendon, with the exception of the pronator teres which inserts just above the medial epicondyle and the coronoid process of the ulna (Figure 2Go). The lateral group of muscles include supinator and brachioradialis and the extensors of the wrist and hand (extensor carpi radialis, extensor digitorum, extensor digiti minimi and extensor carpi ulnaris). They insert onto the lateral epicondyle as the common extensor origin (Figure 3Go).



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  		Figure 3. Normal anatomy. Coronal T1 weighted image demonstrating the common extensor origin (arrow) inserting onto the lateral epicondyle.

 
The anterior group is comprised of the biceps brachii and brachialis muscles. The biceps tendon lies in a superficial position above the elbow, dipping down between the medial and lateral muscle groups to insert onto the radial tuberosity (Figures 4, 5 and 6GoGoGo). The posterior group includes triceps and anconeus.



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  		Figure 4. Normal anatomy. Axial T1 weighted image at the level of the olecranon (marked olec) demonstrating the biceps tendon (white arrow) and the median nerve (white arrowhead) adjacent to the brachial artery. The ulnar nerve (black arrowhead) is seen lying in the ulnar groove.

 


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  		Figure 5. Normal anatomy. Axial T1 weighted image demonstrating the biceps tendon (arrow) as it dips down between the medial and lateral muscle groups.

 


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  		Figure 6. Normal anatomy. Axial T1 weighted image demonstrating the insertion of biceps tendon onto the radial tuberosity.

 
The olecranon bursa lies between the olecranon process and subcutaneous tissues. The deep intratendinous bursa is situated within the substance of the triceps muscle and inserts onto the tip of the olecranon process. The cubital or bicipitoradial bursa is located at the distal biceps tendon insertion onto the radial tuberosity [4].

Several neurovascular structures run in close proximity to the elbow joint. The ulnar nerve runs in a groove on the posteromedial surface of the distal humerus, where it is vulnerable to trauma and entrapment syndromes. The median nerve runs in the antecubital fossa beneath the bicipital aponeurosis, before perforating pronator teres and the radial nerve passes between the brachialis and brachioradialis muscles (Figure 4Go). The brachial artery runs through the antecubital fossa on the medial side of the biceps tendon, between the tendon and the median nerve. The artery divides into radial and ulnar arteries at the level of the radial head. The cephalic and basilic veins, lateral and medial, respectively, run in the anterior superficial soft tissues.


   Disorders of the elbow
Top
 Summary
 Imaging modalities
 Normal anatomy
 Disorders of the elbow
Conclusion
 References
 
Acute trauma
The ligaments and tendons of the elbow are highly susceptible to acute injury, either as a result of activities such as throwing or lifting, or direct trauma. Patients usually present with pain and limitation of movement.

Acute tendon injuries
Biceps tendon tears tend to occur in middle-aged men or weight-lifters, as a result of lifting a heavy object. The injury generally involves the distal tendon at the radial tuberosity attachment. There is retraction of the proximal tendon remnant and muscle belly, which is seen on clinical examination as the "Popeye sign" (Figure 7Go).



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  		Figure 7. The "Popeye" sign. There is retraction of the biceps muscle belly indicating biceps tendon rupture.

 
Both MRI and US can be used for confirming biceps tendon tears and locating the retracted tendon remnant, thus assisting in surgical planning [5–7]. On US the attachment of biceps to the radial tuberosity may however be difficult to visualize, as the tendon courses in an oblique plane and may be prone to anisotropy. Subsequently, partial tears may inadvertently be overlooked. With the probe angled at 45° to the tendon visualization is improved (Figures 8 and 9GoGo). On MRI the sagittal and axial sequences are the most informative (Figures 10 and 11GoGo). A chronic biceps tendon tear may result in atrophy of the tendon and muscle belly with fatty infiltration of the muscle.



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  		Figure 8. Normal ultrasound anatomy. Longitudinal ultrasound demonstrating the distal biceps tendon (arrows) inserting onto the radial tuberosity (R.T.).

 


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  		Figure 9. Longitudinal ultrasound demonstrating a rupture of the distal biceps tendon with fluid/haemorrhage in the gap. Doppler shows the position of the brachial vessels.

 


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  		Figure 10. Sagittal short tau inversion recovery image demonstrating rupture of the distal biceps tendon with retraction of the tendon ends (arrows).

 


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  		Figure 11. Axial T2 fat saturated image demonstrating the proximal retracted tendon end with high signal oedema and haemorrhage at the musculotendinous junction.

 
The triceps tendon is not commonly injured. Acute tears may result from direct blows to the posterior aspect of the elbow or from a deceleration force applied to the arm in extension [8, 9].

Collateral ligament injury
Lateral collateral ligament injury results in posterolateral instability and may be associated with lateral epicondylitis. Deficiency of the ligament occurs most commonly as a result of elbow dislocation [10] but has also been reported following elbow surgery [11]. The ligament may be assessed using both ultrasound and MRI (Figures 12 and 13GoGo).



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  		Figure 12. Normal anatomy. Longitudinal ultrasound image demonstrates the common extensor origin (arrowheads) which overlies the lateral collateral ligament (arrows).

 


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  		Figure 13. Longitudinal ultrasound image demonstrates absence of the lateral collateral ligament (arrows) indicating a tear. The common extensor origin is intact (arrowheads).

 
The medial collateral ligament (MCL) is also essential for elbow stability. The anterior bundle of the MCL is the primary medial constraint and injury to this ligament can result in valgus instability in athletes involved in overhead throwing sports such as baseball and American football. Subsequently, these injuries are less commonly encountered in Europe than in North America. Chronic valgus instability can result in medial epicondylitis, ulnar neuropathy, posteromedial olecranon impingement and osteophytes and loose body formation [12].

Plain radiographs may reveal calcification within the anterior bundle of MCL, osteophytes arising from the olecranon, loose bodies, osteochondral lesions of the capitellum or occasionally avulsion fractures of the medial epicondyle [13].

MCL tears can be demonstrated by MRI or US [14]. US allows dynamic assessment of stability [14] but MRI has the advantage of being able to assess bony causes of medial elbow pain. With injury periligamentous or bone marrow oedema may be seen on short tau inversion recovery (STIR) or T2 weighted fat saturated images. Full-thickness tears of the MCL are accurately identified with MRI, but partial-thickness tears are less easily diagnosed as these involve the deep portion of the anterior bundle of MCL. MR arthrography improves the detection of these partial tears [15, 16].

Fractures
Stress fractures of the coronoid process and olecranon in adults or the olecranon physis in adolescents are seen in association with throwing activities. MRI is very useful for the diagnosis of radiographically occult [17] or suspected stress fractures [18]. T1 weighted images typically demonstrate a well defined low signal fracture line. On T2 weighted or STIR images, a hypointense fracture line is seen surrounded by a hyperintense zone of marrow oedema. Acute bony trauma is covered in a separate section.

Chronic localized pain
Chronic localized pain usually results from overuse injuries. The term "tendinosis" rather than "tendonitis" should be applied to the spectrum of chronic overload injury to tendons, as pathologically there is a paucity of inflammatory cells. Recurrent microtrauma leads to fibrosis, scarring and degeneration of the tendon.

"Epicondylitis" is a term used to describe tendinosis of either the common extensor or common flexor tendons. Lateral epicondylitis or "tennis elbow", is the most common source of elbow pain in the general population and may be produced by a variety of overuse activities. Medial epicondylitis, or "golfer's elbow", is much less common than its lateral counterpart.

MRI and US are both able to demonstrate epicondylitis. On MRI the normal common flexor and extensor tendons are seen as smooth well defined black structures of uniform thickness on all sequences. Epicondylitis is manifest by thickening and signal change. In the early stages, the tendon demonstrates poorly defined low to intermediate signal change on T1 weighted images, with a relative increase in signal on T2 weighted images. With fat suppression or STIR imaging, the affected tendon may return high signal. In later stages, cystic change may occur, with focal areas of high signal seen within the tendon on T2 weighted images. This may be complicated by partial or complete tears of the tendon and be associated with collateral ligament derangement [19, 20] (Figure 14Go).



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  		Figure 14. Coronal short tau inversion recovery image demonstrating high signal in the common extensor origin (arrow) consistent with lateral epicondylitis.

 
On US epicondylitis is manifest by a thickened tendon with loss of homogeneous internal echotexture and increased flow on Doppler examination [21–23]. There may be features of an enthesopathy with irregularity of the bony attachment (Figure 15Go).



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  		Figure 15. Longitudinal ultrasound image demonstrating increased flow within the common extensor origin indicating lateral epiconylitis.

 
Triceps tendinosis may occur in association with olecranon bursitis. Enthesophyte formation at the tendon attachment may be seen on plain radiographs. Ultrasound lends itself well to demonstrating pathology in this superficial structure.

Diffuse pain
Synovitis
Diffuse elbow pain is a very common presenting complaint from patients with elbow disorders. Most often the underlying cause is synovitis, inflammation of the synovium. Synovitis represents a non-specific response to a wide range of insults, including infection, inflammatory arthropathy, degenerative disease, and trauma [24] (Figures 16 and 17GoGo).



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  		Figure 16. Sagittal T1 weighted image demonstrating elevation of the anterior (arrows) and posterior (arrowheads) fatpads indicating synovitis, in a patient with rheumatoid arthritis.

 


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  		Figure 17. Sagittal short tau inversion recovery image demonstrating high signal within the elbow joint indicating a joint effusion or synovial hypertrophy.

 
US demonstrates fluid in the joint, with elevation of the fatpads, with or without a solid synovial component. On Doppler examination there may be increased flow to the synovium. On MRI the distended joint returns fluid signal on T2 weighted and STIR sequences, with low to intermediate signal on T1 weighted sequences. Synovial thickening or plicae may be seen. Synovial hypertrophy can be identified by enhancement with intravenous gadolinium (Figure 18Go).



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  		Figure 18. Longitudinal ultrasound demonstrating fluid (arrow) in the olecranon fossa (arrowheads) in a patient with an inflammatory synovitis.

 
Haemophilia is one of the few causes of synovitis which may be easily recognised by MRI, as haemosiderin deposits from recurrent intra-articular haemorrhage give rise to low signal deposits within the joint [25]. Haemosiderin is more conspicuous on gradient echo sequences due to susceptibility artefact. Similar low signal synovial deposits may also be seen in pigmented villonodular synovitis, but this is rarely encountered in the elbow [26] (Figure 19Go).



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  		Figure 19. Sagittal gradient echo image demonstrating synovitis with low signal deposits within the synovial lining consistent with haemosiderin, in a patient with haemophilia.

 
Osteoarthritis
Osteoarthritis (OA) of the elbow is typically seen in men, usually aged over 40 with a history of work or sports related overuse or previous trauma [27]. Plain radiographs usually show spurring of the anterior margin of coronoid and posterior margin of the olecranon. Both MRI and CT may be used for differentiating bony loose bodies from osteophytic spurs. The articular cartilage is best seen on gradient echo and fat suppressed MRI sequences, particularly when arthrography has been performed. Deep fissuring, cartilage loss, marginal spurring and loose body formation are well recognised features of OA. With age-related OA, articular cartilage loss is more common in radiohumeral articulation than the ulnohumeral joint [28]. Chondral defects tend to be seen in the posterolateral aspect of the trochlear notch in sports related overuse [29].

Locking
Loose bodies
After the knee, the elbow is the second most common site for loose bodies. Loose bodies are thought to arise from a small nidus of bone or cartilage within the joint that results from fragmentation of the articular cartilage associated with OA, osteochondral fractures or osteochondritis. The nidus receives nutrition from the synovial fluid and grows in a laminar fashion [30]. Patients usually present with loss of motion and intermittent locking.

Plain radiography should be the first investigation when loose bodies are suspected [31]. Loose bodies are usually easily identified if ossified, but may be missed if they are cartilaginous or located deep in the humeroulnar joint. Differentiating loose bodies from osteophytes or extra-articular ossicles may also be difficult on plain radiography.

Ultrasound is an excellent technique for demonstrating loose bodies [31, 32]. Joint injection with saline has been shown to improve the ultrasound evaluation and conspicuity of small and radiographically occult loose bodies [33] (Figure 20Go).



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  		Figure 20. Sagittal ultrasound demonstrating an echogenic mass in the olecranon fossa consistent with an ossified loose body.

 
Both CT and MRI are able to accurately identify and localize loose bodies particularly in the presence of a joint effusion or intra-articular contrast [31, 34]. Osteophytes, hypertrophied synovium and air bubbles may however mimic loose bodies.

Synovial osteochondromatosis
Synovial osteochondromatosis (SOC) is a disorder characterized by metaplasia of the subsynovial soft tissues that results in cartilage formation within the synovium [35]. This condition should be differentiated from other causes of loose bodies, such as osteochondral fractures and OA with fragmentation of the articular surface [36]. It is usually a monoarticular process but occasionally arises within a bursa or tendon sheath. Men are more commonly affected than women and the average age is about 40 years. The usual presentation is with locking, pain and swelling.

The process appears to follow a temporal sequence characterized by three recognisable phases. (1) active synovial disease only, with no loose bodies; (2) transitional disease with both active synovial proliferation and free loose bodies; and (3) multiple free osteochondral bodies with no active synovial disease [35]. On plain radiographs, the condition is recognised by the widening of the joint space, bony erosions, displacement of the intra-articular fat pads and the presence loose bodies within the elbow (Figure 21Go). In the early stage of disease there is no calcification or ossification present. Secondary degenerative change occurs in the later stages of the disease. CT shows thickening of the synovium with loose bodies within the joint. On MRI, the calcified foci are seen as signal voids on all pulse sequences [37]. These signal void foci are more prominent on gradient-echo sequences due to susceptibility artefact. Ossified bodies may contain central marrow fat in advanced stages. In early stage disease no ossific foci may be present. Nodules of cartilage are bright on T2 weighted images and may mimic fluid on MRI (Figure 22Go).



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  		Figure 21. Plain radiograph demonstrating several ossified loose bodies within the elbow in a patient with synovial osteochondromatosis.

 


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  		Figure 22. Sagittal gradient echo image demonstrating a mixed signal loose body in the olecranon fossa in a patient with synovial osteochondromatosis.

 
Osteochondrosis and osteochondritis dissecans
Osteochondrosis in the elbow is a developmental anomaly that usually affects the capitellum (Panner's disease). It is a benign, self-limiting abnormality, typically occurring in boys between 7 and 12 years of age, prior to complete ossification of the capitellum. Plain radiographs reveal a mottled epiphysis with fragmentation. Reconstitution of the capitellum eventually occurs. On MRI the ossified epiphysis has decreased signal intensity on T1 weighted images [38]. The articular surface typically remains intact. Loose body formation and significant residual deformity of the capitellum are not usually seen.

Osteochondritis dissecans (OCD) is a localized lesion of bone and cartilage that typically involves the anterior aspect of the capitellum in adolescents and young adults [39]. This condition is thought to represent avascular necrosis as a result from chronic lateral impaction due to valgus stress, which is especially common in baseball pitchers and gymnasts [40]. The lesion consists of a segment of subchondral bone and cartilage, which may remain in situ and heal, or undergo detachment, leading to loose body formation and eventually degenerative joint disease.

Plain radiographs may depict a localized area of subchondral lucency or defect in the capitellum, with or without a loose body. MRI is useful for detecting radiographically occult lesions, which appear as intermediate to low signal subchondral lesions on T1 weighted images and high signal on T2 weighted or STIR imaging. Staging accuracy is improved by performing MR arthrography [41]. Unstable lesions are characterized by fluid or contrast encircling the osteochondral fragment. The intra-articular contrast also aids in the identification and localization of loose bodies. Intravenous gadolinium has been used to determine the viability of the OCD fragment [42] but in practice is not usually necessary. Loose in situ lesions may be demonstrated by enhancing granulation tissue seen beneath the osteochondral fragment [42] (Figures 23Go and 24Go).



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  		Figure 23. Coronal short tau inversion recovery image demonstrating an osteochondral defect of the capitellum with some minor surrounding oedema, in addition to an intra-articular loose body (arrowheads).

 


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  		Figure 24. Same patient as Figure 23Go. Sagittal T1 weighted image demonstrating an osteochondral defect of the capitellum (arrow).

 
A diagnostic pitfall to be aware of is the pseudodefect of the capitellum, which is seen as a trough at the junction of the non articular portion of the lateral condyle with the cartilage covered capitellum [43]. It is seen on both sagittal and coronal images and is more conspicuous when fluid is present within the joint. It is characteristically located posteriorly, whereas OCD is found anteriorly.

Localized swelling
Bursitis
The olecranon bursa is the most common site of superficial bursitis in the body. It is usually due to chronic trauma and is also known as miner's elbow or student's elbow [44, 45]. Olecranon bursitis may also be secondary to systemic disease such as a rheumatoid arthritis, gout and calcium pyrophosphate deposition [46]. Acute bursitis due to infection is the cause in up to 20% of patients, the most common organism being Staphylococcus aureus [47].

On US the bursa may appear as a mixed solid and fluid mass, which may be fluctuant. Doppler interrogation usually reveals increased flow (Figure 25Go). MRI of olecranon bursitis may demonstrate a heterogeneous mass due to acute or chronic haemorrhage superimposed on synovitis (Figure 26Go). Infiltration of the subcutaneous fat and cellulitis may accompany septic bursitis. Osteomyelitis of the underlying olecranon is uncommon complication (Figure 27Go).



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  		Figure 25. Longitudinal ultrasound demonstrating an enlarged fluid filled olecranon bursa (arrows).

 


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  		Figure 26. Sagittal short tau inversion recovery image demonstrating a grossly enlarged and inflamed olecranon bursa (arrows).

 


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  		Figure 27. Axial gradient echo image demonstrating a low signal sequestrum (white arrow) in the olecranon indicating osteomyelitis. There is also a septic arthropathy (black arrows).

 
The deep bursa in the elbow is the bicipital radial or cubital bursa, which separates the distal biceps tendon from the radial tuberosity [48, 49]. Inflammation of the cubital bursa may accompany tendinosis and tear of the distal biceps tendon [4, 49]. If there is marked synovial hypertrophy this may lead to the misdiagnosis of a neoplasm (Figures 28Go and 29Go).



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  		Figure 28. Sagittal T2 weighted image demonstrating a fluid signal mass (arrows) surrounding the biceps tendon consistent with cubital bursitis.

 


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  		Figure 29. Sagittal short tau inversion recovery image demonstrating a heterogeneous high signal lobulated mass (black arrows) surrounding the biceps tendon (arrowheads) consistent with marked synovial hypertrophy in the cubital bursa (asterisks), in a patient with psoriatic arthropathy of the elbow.

 
Entrapment neuropathy
Due to the unique anatomy of the elbow, it is a common site for entrapment neuropathies, which may occur due to friction, traction or compression of the nerve. The diagnosis of nerve entrapment at the elbow has traditionally relied on clinical findings and electromyography [50, 51]. Increasingly however, US and MRI have been used to detect structural causes of nerve entrapment.

Numbness and paresthesia involving the little finger and the medial half of the ring finger are common complaints with ulnar nerve compression. There may also be weakness and wasting of the intrinsic muscles of the hand. US may reveal dynamic dislocation of the ulnar nerve, osteophytes in the ulnar groove or a mass in the ulnar groove. There may also be focal thickening of the nerve (Figure 30Go).



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  		Figure 30. Axial ultrasound demonstrating displacement of the ulnar nerve (arrow) due to an osteophyte (arrowhead) in the ulnar groove.

 
Entrapment of the radial nerve may occur just distal to the elbow as the posterior interosseous nerve branch passes into supinator muscle, leading to the "supinator syndrome" [51]. Typically there is localized pain and the patient is unable to extend the fingers at the metacarpophalngeal joints. Elbow dislocations, fractures, inflammatory arthritis or soft tissue masses may be responsible [52]. The posterior interosseous nerve itself may appear swollen. The median nerve is most commonly compressed at the elbow by the ligament of Struthers which extends down from a supracondylar process. Soft tissue masses or a hypertophied pronator teres muscle may also result in compression [51].


   Conclusion
Top
 Summary
 Imaging modalities
 Normal anatomy
 Disorders of the elbow
 Conclusion
References
 
Plain radiography remains very important in the evaluation of elbow pain and dysfunction, and should be performed routinely prior to cross-sectional imaging. US is extremely useful for evaluating the soft tissue structures of the elbow and for detecting synovitis or effusions, but does not allow bony assessment. MRI is a very powerful tool for assessing both the soft tissue and bony structures of the elbow together.


   References
Top
 Summary
 Imaging modalities
 Normal anatomy
 Disorders of the elbow
 Conclusion
 References
 

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