Adult Reconstruction, 1st Edition

Section IV - Elbow Reconstruction

Part A - Evaluation

48

Imaging of the Elbow

Jeffrey C. King

The elbow joint is a complex structure with three separate intracapsular articulations. These are highly congruent joints with multiplanar, noncollinear surfaces that make imaging difficult. The relatively small amount of overlying soft tissue and the ease of positioning, however, aid in imaging efforts. As with other joints, multiple imaging tools are available. The most commonly used include plain radiographs, computed tomography, and magnetic resonance imaging. Arthrography is often a useful adjunct to these studies, but is less commonly used alone. Ultrasound may be helpful in some situations where dynamic images are required. Plain tomography and xeroradiography have largely been replaced by newer, better studies and are mentioned here for the sake of completeness.

This chapter will review current imaging modalities for the elbow, including appropriate techniques and parameters. Guidelines to assist in choosing the appropriate test for specific clinical situations will be discussed.

Plain Radiographs

Anteroposterior (AP) and lateral radiographs remain the workhorses of elbow imaging. The AP view (Fig. 48-1A) demonstrates the distal humeral articular surface, medial and lateral epicondyles, radial head and neck, and most of the proximal ulna, excluding clear views of the coronoid and olecranon processes. The ulnohumeral and radiocapitellar joint spaces are well seen and can demonstrate widening or narrowing depending on the clinical condition. The lateral radiograph (Fig. 48-1B) clearly shows the coronoid and olecranon processes, as well as the associated fossa. The radial head overlies the coronoid, but should still allow adequate visualization of both structures. Adequacy of the lateral view can be determined by the target sign of three concentrically larger circles seen in the distal end of the humerus. These rings represent, from inside out, the minimum dimension of the trochlea, the capitellum, and the medial rim of the trochlea. Malrotation by as little as 5 degrees will disrupt this appearance. Anterior and posterior fat pads can be seen in situations of intra-articular distension (Fig. 48-2). The supinator fat stripe can be displaced by swelling associated with radial head fractures.

The AP view is obtained with the elbow fully extended on an appropriately sized image receptor. The arm is parallel with the plate, and the forearm is in supination. The beam is directed perpendicular to the midpoint of the elbow joint, and the joint is centered on the film. The lateral view is obtained with the shoulder abducted to 90 degrees, the arm parallel to the plate, and the forearm in full supination. The beam is directed perpendicular to the elbow joint, or ideally at a 7-degree caudal angle to replicate the carrying angle.

In situations where full extension of the elbow is not possible, the AP view can be compromised (Fig. 48-3). A single AP view obtained through a flexed elbow is of little value. In this situation, two views—an AP view of the proximal forearm and an AP view of the distal humerus—should be obtained.

The forearm view is obtained with the forearm placed flat and the elbow joint centered on the plate. A greater degree of flexion deformity will require increased kilovoltage (Kvp) to allow adequate penetration to demonstrate bony detail. The humerus view is obtained with the distal humerus flat on the plate with the elbow centered. The forearm should be supported for comfort. The beam is directed perpendicular to the elbow joint.

Additional views are obtained to visualize specific features of the elbow anatomy. The internal (medial) oblique view improves visualization of the trochlea, olecranon, and coronoid. The external (lateral) oblique view improves visualization of the radiocapitellar joint, radioulnar joint, medial epicondyle, and coronoid tubercle.

The internal oblique view is obtained with the arm positioned initially as for an AP view. The arm is then rotated internally 45 degrees. The beam is directed perpendicular to the plate and elbow joint. The external oblique view is obtained by rotating the arm externally 45 degrees.

The radial head is better visualized with the radial head view and lateral radial head rotation positions. The radial head view (Fig. 48-4) minimizes the overlap of the radial head and coronoid, improving visualization of radial head and capitellar pathology. Visualization of the fat pads is enhanced as well. The lateral rotation positions demonstrate

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the radial head in profile throughout its full available arc of motion. The radial tuberosity is the most obvious indicator of the position of forearm rotation. The coronoid is viewed without superimposition with the coronoid-trochlea position.

The radial head view is obtained by positioning the elbow in the standard lateral position and angling the beam 45 degrees cephalad, parallel to the long axis of the humerus. The lateral rotation positions require standard lateral position of the elbow and perpendicular beam position. The forearm is then positioned in hypersupination, midsupination, midpronation, and hyperpronation. The coronoid-trochlea image is obtained by positioning similar to the radial head view, but angling the beam 45 degrees caudal.

There are several special axial views of the elbow. These include the axial olecranon projection view, which enhances the visualization of the olecranon margins and associated spurs; also, the cubital tunnel view demonstrates any bony abnormalities or encroachment on the ulnar nerve in the cubital tunnel.

The axial olecranon projection view is obtained with the proximal dorsal forearm flat against the plate, full supination, and maximal elbow flexion with the humerus overlying the forearm. The beam is angled 20 degrees toward the hand along the long axis of the forearm. The cubital tunnel view is obtained by placing the humerus flat on the plate, maximal flexion of the elbow, and 15 degrees of external rotation of the arm. The beam is directed perpendicular to the plate and elbow joint.

Finally, a gravity stress view may be used for evaluation of valgus instability. This technique can minimize apprehension but requires patient relaxation and cooperation to avoid a false-negative result. Gravity-induced valgus instability is demonstrated by widening of the joint space of the medial side of the joint.

This is a cross-table view, with the patient supine and the arm abducted 90 degrees away from the side. The arm is externally rotated, the thumb pointing to the floor. The

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elbow is flexed 15 degrees. The plate is oriented vertically and placed dorsal to the elbow. The beam is directed horizontally, perpendicular to the elbow joint.

Plain Radiograph Interpretation

Specific osseous structures and relationships should be systematically reviewed and irregularities noted, and when indicated, additional views or studies obtained. On all views the radial head should line up with the capitellum. The radiocapitellar and ulnohumeral joint space should be symmetric on the AP view; the coronoid-trochlear and the olecranon-trochlear joint spaces should be symmetric on the lateral view. Visualization of the anterior and posterior fat pads on the lateral radiograph (Fig. 48-2) is a reliable sign of intra-articular fluid collection, most common with trauma or inflammation. Occult fracture should be sought when accompanied by a history of trauma. Finally, for all of the utility of plain radiographs, they still present a two-dimensional representation of a three-dimensional structure. The ability of computed tomography and magnetic resonance imaging to present the elbow anatomy in three dimensions underscores their importance as an adjunct to the diligent history taking and careful physical examination in the diagnosis of elbow pathology.

Computed Tomography

Computed tomography (CT) has largely supplanted the use of plain tomography in this country. CT has the advantage of clearer images and multiplanar views over plain tomography, although metal artifact remains a limitation. Three-dimensional rendering of the elbow joint is possible as well (Fig. 48-5). The decreased slice thickness and helical image acquisition of the newest scanners provide for improved clarity of reconstructed images. Nonaffected bones can be digitally subtracted to allow improved visualization of the involved area (Fig. 48-6). This is especially helpful in complex coronoid fractures as well as for preop planning for elbow malunion surgery. The injection of radio-opaque dye with or without air (single- or double-contrast arthrogram) provides more sensitive evaluation of cartilaginous loose bodies and the status of the articular cartilage. The author believes that

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CT arthrogram provides the best evaluation for loose bodies in the elbow with catching and/or locking, although other literature demonstrates no advantage of CT arthrogram over MRI evaluation.

Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) provides the highest-quality images of the soft tissues about the elbow. As more imaging protocols emerge, the utility of this technology broadens. MRI should be used, however, to test a specific hypothesis, developed by the history and clinical examination, rather than as a “fishing expedition” on any and all painful elbows. The nature of the suspected problem determines the positioning and imaging protocols used to evaluate the elbow. Common indications include collateral ligament injuries (Fig. 48-7A, B), osteochondritis desiccans, and partial biceps injuries. MRI is not usually required in complete biceps tears with retraction or in the setting of traumatic fracture/dislocations where significant soft tissue injury can be assumed. Some have advocated the use of MR arthrogram to improve the sensitivity of collateral ligament injury diagnosis. Imaging can be performed safely with implanted metallic plates and screws, although scatter artifact limits image clarity.

Normal tendinous structures appear dark on T1- and T2-weighted images (Fig. 48-7A). Fluid and edema appear bright on the T2-weighted images, indicating soft tissue injury. Avascular bone appears dark on T1 images surrounded by the brighter signal of the normal cancellous bone. A fast spin echo, T2-weighted image with fat suppression is used to best image the collateral ligaments (Fig. 48-7B). Special positioning improves the image acquisition in patients with distal biceps injuries (Fig. 48-8).

Ultrasound

Ultrasound has been used to evaluate elbow tendons, ligaments, muscles, peripheral nerves, and joint structures. Advantages to ultrasound include accessibility, low cost, portability, and lack of contraindications (unlike MRI). In several specific applications, elbow ultrasound is the preferred imaging method, even over MRI. One such application is dynamic imaging of the elbow, where abnormalities may be present only with specific joint movements or

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position. Examples include ulnar nerve dislocation and snapping triceps syndrome, which occurs with elbow flexion. An additional dynamic examination of the elbow under ultrasound observation is assessing injury to the anterior bundle of the ulnar collateral ligament with valgus stress applied to the elbow. Another advantage of ultrasound is evaluation of soft tissues superficial to metal hardware free of artifact. Peripheral nerves can also be efficiently evaluated with ultrasound, such as evaluation for the radial nerve injury after plate fixation of a humeral diaphyseal fracture.

Clinical Scenarios

Trauma

Imaging of the traumatized elbow usually starts with plain radiographs. Additional radiographic images should be included as indicated for specific pathology (Table 48-1). Evidence of associated fracture should be sought in all cases of elbow dislocation, as this affects treatment and prognosis. Thin-cut CT with multiplanar reconstructions are especially helpful in the evaluation of coronoid and capitellum fractures, as well as intracapsular distal humerus fractures. The CT images often demonstrate more significant pathology than suspected on plain films. Three-dimensional reconstructions with digital subtraction of uninvolved bony structures allow excellent visualization of complex intra-articular pathology. MR imaging provides excellent soft tissue definition, but is rarely indicated in high-energy trauma. Certain soft tissue injury patterns are common, such as lateral ulnar collateral ligament injury associated with radial head and coronoid fracture, and should be anticipated. MRI has increased utility in the evaluation of musculotendinous and ligamentous trauma, such as acute throwing injuries and biceps tendon pathology. Special imaging protocols have been developed to improve diagnostic accuracy.

Instability

Symptoms of instability may be acute or chronic. In the case of acute instability, the above trauma recommendations apply. Chronic instability is largely a clinical diagnosis. MRI is less sensitive in delineating attenuated ligamentous structures unless there is a superimposed acute on chronic injury. Gravity stress radiographs may confirm the diagnosis of valgus instability. In cases of posttraumatic chronic instability, CT images may clarify the competence of key structures such as the anterior and medial coronoid and radial head. Evaluation of the joint with real-time fluoroscopy before surgical procedures can be invaluable in clarification of instability patterns Examination of the awake patient to determine patterns of instability can be unreliable. It is highly recommended that all patients with a question of instability undergo a fluoroscopic examination after general anesthesia but prior to sterile surgical preparation of the patient.

Stiffness

Elbow stiffness may be related to soft tissue contracture, bony block, or most commonly, both causes. Plain films demonstrate bone causes such as heterotopic ossification (HO), loose bodies, or joint incongruity. CT scanning provides three-dimensional visualization of the bony abnormality and can be helpful in preoperative planning. Certain patterns of heterotopic bone formation are common. Posttraumatic HO typically occurs in the anterior lateral aspect of the joint. In cases of neuromuscular or burn HO, the posterior medial joint is most commonly involved. The ulnar nerve may be completely encased in bone;

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nevertheless, surprisingly, it almost always functions normally. CT images may clarify whether the ankylosis is complete or incomplete; in the latter case removal is simplified. MRI is of limited value in cases of soft tissue contracture and is not recommended.

The Painful Elbow

There are many causes for the painful elbow, and imaging is a useful adjunct in diagnosis (Table 48-2). The traumatized elbow is discussed above. In young athletes, osteochondritis dissecans (OCD) and apophysitis should be considered. These may be seen on plain x-ray films (contralateral images should be obtained), but MRI may be needed in early or subtle presentations. MRI or bone scan will demonstrate stress fractures, not seen on plain x-ray views. In cases of painful catching or locking, with or without limitation of motion, the author uses CT arthrogram to evaluate for loose bodies if the plain films are inconclusive. If the CT is positive, loose body removal is recommended; if negative, a symptomatic plica may be the cause of the symptoms. Throwers and other overhead athletes with medial elbow pain rarely exhibit gross instability. A medial stress view may show widening of the medial joint. An axial olecranon view may show posterior medial osteophytes associated with valgus extension overload syndrome. Finally, MRI may demonstrate medial collateral ligament (MCL) pathology or flexor pronator mass inflammation. Ulnar nerve instability may cause medial-sided pain. This is well evaluated by ultrasound. Ultrasound is also useful for demonstrating the snapping triceps syndrome, owing to the dynamic nature of the image acquisition. Additional imaging is rarely indicated in clinical cases of medial or lateral epicondylitis. Plain films may show periosteal reaction at the involved epicondyle. MRI adds little to the diagnosis or treatment of this condition. Avascular necrosis of the distal humerus is occasionally seen in patients on high-dose steroids, with alcoholism, or other lipid metabolism disorders. This may be seen on plain films, but often late in the course. MRI will demonstrate low-signal intensity of avascular bone on T1 images before changes can be detected on plain radiographs. Osteoarthrosis and inflammatory arthropathies are typically well visualized on plain x-ray films. CT is occasionally helpful to determine the extent of joint space involvement. Anterior cubital fossa pain, especially with resisted flexion and supination, may indicate a partial biceps injury. MR imaging can identify partial biceps injury or associated pathology. Ultrasound can provide similar information, often at lower cost, but the results are more operator dependent.

Conclusion

There are more options than ever before to provide high-resolution images of the bone and soft tissue anatomy of the elbow. Plain radiographs remain the appropriate initial choice in the diagnosis of many conditions and may indicate the need for confirmatory studies. MR imaging is most useful for the imaging of the soft tissues, whereas CT best defines the bony anatomy. Fluoroscopy and ultrasound provide motion images in real time, improving the diagnosis of dynamic conditions such as snapping triceps and instability patterns. All of these studies provide invaluable information to supplement, rather than replace, a careful history and physical examination for the diagnosis of complex elbow problems.

Suggested Readings

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