Applied Radiology

In the evaluation of small extremity joints such as the elbow and wrist, MR has demonstrated that it is an ideal imaging modality, due to its high contrast and direct multiplanar capabilities. With recent advances in software and new surface coil designs, detailed evaluation of ligaments, tendons, and cartilage can easily be performed.

Volumetric gradient-recalled echo imaging allows for thin section imaging as well as image reconstruction in multiple planes, which can be extremely useful in patients who cannot maintain rigid positioning during the MR examination.

Elbow and wrist pain are common presenting complaints in patients who are referred to orthopaedic surgeons. While the underlying diagnoses often can be made on clinical assessment, more difficult diagnoses, such as distinction between elbow ulnar collateral ligament and flexor tendon pathology, are difficult to discern. In addition, the extent of injury cannot always be accurately assessed. MRI is useful for both establishing the correct diagnosis and for evaluating extent of injury, which aids in the surgical planning of patients refractory to conservative treatment. Dedicated cartilage pulse sequences also may disclose clinically unsuspected chondral injury as the underlying cause of persistent pain.

The elbow

The elbow is a synovial hinge joint between the trochlea and the capitellum of the humerus, articulating with the trochlea notch of the olecranon and the radial head.1 The lateral collateral ligament is a single band with its apex attached to the lateral epicondyle of the humerus and its base attached to the upper margin of the ulnar band of the lateral collateral ligament.1 The ulnar band of the lateral collateral ligament crosses posterior to the radial neck and inserts on the supinator crest of the ulna. The ulnar band of the lateral collateral ligament, as well as the anterior band of the anterior bundle of the medial collateral ligament, are primary ligamentous stabilizers of the elbow. Important musculotendinous origins of the lateral elbow include the extensor carpi radialis brevis and extensor carpi radialis longus tendons. These tendons course lateral to the lateral collateral ligament, originating from the lateral epicondyle of the humerus (figure 1).

The medial collateral ligament is composed of anterior and posterior oblique bundles originating from the medial epicondyle of the humerus, and a transverse bundle extending between the coronoid and the tip of the olecranon.2 The stronger anterior bundle inserts into the medial aspect of the coronoid process of the ulna, with the weaker, thinner, and more variable posterior bundle inserting into the posteromedial aspect of the olecranon.3 The anterior bundle is divided into anterior and posterior bands and is best visualized with the elbow in extension.2 The posterior bundle is best visualized with the elbow in flexion. Important musculotendinous origins of the medial elbow include the common flexor and pronator tendons, which originate from the medial epicondyle. These include the flexor carpi radialis, flexor digitorum superficialis, pronator teres, palmaris longus, and flexor carpiulnaris tendons.

MR imaging

The inherent obliquity of the elbow joint requires proper patient positioning to maximize optional visualization of tendon and ligament anatomy. To maximize patient comfort and thereby minimize motion, we evaluate the elbow with the patient in a supine position, with the elbow at the side. We favor this position over the "hand-over-the-head" position. To achieve coronal images, the forearm is supinated and a 5-inch receive-only surface coil or phase-array shoulder coil is placed anteriorly over the elbow. Coronal 3D volumetric gradient-recalled echo or multiplanar gradient-recalled echo technique is initially performed, as the long axis of the ligaments and tendons are most easily assessed in this plane. Specific pulse sequence parameters include thin (1.4 to 1.6 mm) slices, field-of-view of 11 to 13 cm, with matrices of 256 ¥ 192 or 256 ¥ 256. To assess cartilage, additional coronal, axial, and sagittal higher resolution (matrices of 512 ¥ 384 or 512 ¥ 256) fast spin echo images also are obtained. The elbow should be imaged in extension unless there is direct interest in the posterior bundle of the medial collateral ligament, in which case additional flexion images are performed. We also chose to image the elbow in the direct coronal plane without intraarticular gadolinium. Other authors have suggested imaging in a 20° posterior oblique coronal plane in relation to the humeral shaft with the elbow extended and, optimally, in a coronal plane aligned with the humeral shaft with the elbow slightly flexed.4 This is because the collateral ligaments course in an approximately 15 to 20° posterior oblique fashion. These same authors assert that intraarticular gadolinium can be useful for delineating the undersurface of normal and abnormal ligaments and for evaluating partial tears at these sites.4 However, at our institution, we have not found intraarticular contrast necessary for routine MR imaging of the elbow.

Lateral elbow

Lateral epicondylitis, also known as "tennis elbow," is a common cause of lateral elbow pain, the diagnosis of which is typically evident on clinical examination. Repetitive trauma to the extensor tendons leads to degeneration and microtears. Histopathologically, there is mucoid degeneration, disruption of collagen fibers, and neovascularization at the origin of the common extensor tendons, which correlate to the signal hyperintensity seen on MR imaging.5 These MR findings are in agreement with previous histopathologic reports, demonstrating disrupted collagen fibers with fibroblastic and vascular ingrowth, but no evidence of an inflammatory component.6

MR imaging of recalcitrant lateral epicondylitis typically demonstrates signal hyperintensity at the origin of the extensor carpi radialis brevis tendon, with separation between the extensor tendons and lateral collateral ligament (figure 2).5 This may progress to complete or partial disruption of the extensor carpi radialis brevis and extensor carpi radialis longus tendons, as well as the lateral collateral ligament. MR imaging evaluates the extent of degeneration, which will help to determine whether surgery involves simple débridement or débridement and repair.

Medial elbow

Medial elbow pain is more difficult to evaluate clinically, as it may be due to medial epicondylitis, medial collateral ligament injury, ulnar nerve injury, or posteromedial impingement. MR imaging has been found to be quite useful in determining site and extent of injury, again directly influencing patient management.

Medial epicondylitis, also known as "pitcher's" or "golfer's elbow," is caused by repetitive strain on the common flexor/pronator muscle group that originates from the medial epicondyle.2 Signal hyperintensity is noted at the origin of the common flexor/pronator muscle group, again with the possible findings of degeneration, partial tear, or complete disruption of the medial epicondyle.

Injuries to the medial collateral ligament occur as increased valgus stress is placed upon the elbow. Valgus stress rarely injures the flexor forearm muscles, as these are more resistant to stress than the ligamentous insertions.2 MR imaging demonstrates foci of abnormal signal intensity and morphologic alteration of the normally hypointense medial collateral ligament.7 Disruption may occur at the humeral or ulnar insertion and may be complete or partial (figure 3). One must be careful not to interpret the normal synovial recess deep to an intact medial collateral ligament as abnormal signal intensity and evidence of partial tear.2 Repetitive valgus stress also may lead to chronic medial collateral ligament tears and a reparative response, which appears as thickening of the ligament and loss of the normal hypointense signal (figure 4).

Extreme valgus load also may result in osteochondral impact injury of the capitellum, rupture of the posterior capsule, and ulnar nerve entrapment (figures 3,5). Cartilage wear over the humeral ulnar articulation is not uncommon (figure 6). However, it is important not to interpret the overhanging edges of the capitellum (pseudodefect of capitellum) as a site of osteochondral impaction injury on the sagittal or coronal sequences.8

In the pediatric athlete, fat suppressed gradient-recalled echo imaging can detect physeal injury to the medial epicondylar apophysis, which is caused by repetitive valgus stress loading of the developing joint (figure 7).2 Subtle injuries of the medial collateral ligament may occur if partial fusion of the apophysis has already occurred (figure 8). Chronic nonunions also may be assessed.

Posterolateral rotatory instability

The ulnar band of the lateral collateral ligament, as stated above, is an important primary stabilizer of the elbow joint. The ulnar band is located at the posterior margin of the radiocapitellar joint and courses from the lateral epicondyle to the supinator crest of the ulna. Tears of the ulnar band allow for rotatory subluxation of the ulna in forearm supination, allowing the radial head to subluxate inferior to the capitellum.9 This clinical entity is called posterolateral rotatory instability of the elbow and it falls within the spectrum of elbow instability prior to complete dislocation.10 Plain radiographs are usually nondiagnostic and subluxation and characteristic reduction may not be demonstrated clinically in the absence of examination under anesthesia. Given the importance of an intact ulnar band of the lateral collateral ligament in stabilization of the elbow joint, the detail of MR imaging serves as an accurate, noninvasive diagnostic tool (figures 9,10).

The wrist

MR imaging of the wrist is becoming a more frequently performed examination. Commonly requested exams include the evaluation of the triangular fibrocartilage complex (TFCC), intrinsic scapholunate and lunotriquetral interosseous ligaments, and occult ganglia of the wrist. MR also is useful in the assessment of tendinopathy, lesions of the carpal tunnel, and cartilaginous injury.

MR imaging

At our institution, MR examination of the wrist is performed with the patient in the supine position and the affected hand at the side, with the forearm in full pronation. Imaging is done using a quadrature design wrist surface coil. Thin slice (1 mm), high resolution (8 cm field-of-view, 256 ¥ 256 matrix) coronal volumetric gradient-recalled echo images, as well as fast spin echo axial, coronal, and sagittal images, are obtained for the examination.

Triangular fibrocartilage complex

The TFCC is a composite of ligamentous and fibrocartilaginous tissue that binds the ulnar aspect of the radius to the ulna and ulnar carpus.11 It is a major stabilizer of the radioulnar and ulnocarpal joints. This complex consists of the volar and dorsal radioulnar ligaments, the articular disc, the meniscal homologue, the ulnolunate and ulnotriquetral ligaments, and the extensor carpi ulnaris tendon sheath.11 The articular disc has a broad attachment to the sigmoid notch of the radius and, along with the remainder of the TFCC complex, has a striated fascicular attachment to the ulna (figure 11). This ulnar attachment is demonstrated as two distinct groups of fascicles, one inserting at the tip of the ulnar styloid process and the other inserting at the base of the ulnar styloid process .11 Less commonly, the ulnar attachment is demonstrated as a band of fascicles attaching along the entire length of the ulnar styloid process. Due to the variable insertion of the TFCC onto the ulna, familiarity with this anatomy is important in order to avoid misdiagnosis of anatomic variation as disc pathology.12,15 Despite this variable anatomy, a recent series of 77 patients noted 97% accuracy in the detection of tear and 92% accuracy in the localization of tear, 57% of which were ulnar in location.16 One also must be careful not to interpret the high signal intensity fluid in the prestyloid recess or adjacent synovial proliferation as a tear at the ulnar insertion of the TFCC.

Injury to the TFCC is a common cause of ulnar wrist pain. Palmer proposed a classification system for TFCC lesions based upon cause (degeneration or traumatic), location, and extent of injury to the articular disc.13 Degenerative tears of the articular disc are more common than traumatic tears; they are more commonly demonstrated at the central portion of the articular disc, with thinning of the adjacent intact fibrocartilage. Traumatic tears have previously been reported to be more common within the central or radial aspect of the articular disc (figure 12).14,15 However, more recent studies demonstrate that the ulnar portion of the articular disc may be the more common location.16 The radial and central aspects of the articular disc are relatively hypovascular, as only the outer 10 to 40% of the articular disc receives direct blood supply.17 This directly influences healing, with radial-side tears usually requiring surgical débridement. MRI has proven to be an excellent modality for detection of injury to the articular disc, prompting either direct repair or débridement, as indicated.

MR imaging also is useful in its ability to evaluate other common differential diagnoses of wrist pain.14 These include tendinopathy, ulnar neuropathy, ulnar artery thrombosis, occult fracture, ganglion formation, and distal radioulnar joint ligament tears. Disruption of the dorsal and/or palmar distal radioulnar ligaments may be associated with injury to the articular disc of the TFCC. The thick dorsal and palmar ligaments extend from the dorsal and palmar rim of the sigmoid notch of the radius to the fovea and base of the ulnar styloid process.15 The primary function of these ligaments is to prevent distal radioulnar joint subluxation. Evaluation of the distal radioulnar joint ligament can be performed when noting increased signal intensity and disruption of ligament fibers on coronal gradient-recalled echo images, as well as altered relationship of alignment of the distal radius and ulna in pronation on fast spin echo axial images (figure 13). MR imaging can therefore confirm the clinical suspicion of distal radioulnar joint subluxation.

Intrinsic ligaments

Another common indication for MR imaging of the wrist is the evaluation of intrinsic scapholunate and lunotriquetral ligament instability in patients with normal plain radiographs and strong clinical suspicion for injury. The scapholunate ligament connects the volar, proximal, and dorsal border of the ulnar aspect of the scaphoid bone to the radial border of the lunate bone.18 Injury to the scapholunate ligament leads to scapholunate instability, which can progress to scapholunate dissociation and rotary subluxation of the scaphoid.19 However, controversy exists as to the clinical significance of lesions in various anatomic portions of the scapholunate ligament. Because it has been reported that only tears extending to the dorsal aspect of the ligament or tears involving the entire ligament affect scapholunate joint stability,18,19 MRI is crucial in detecting not only the tear itself, but the location and extent of the tear (figure 14). Therefore, one must be familiar with the variable shape, signal intensity, and features of attachment to adjacent cartilage or bone of the different portions of the scapholunate ligament, as this directly influences management of these lesions.18 Evaluation of tears of the lunotriquetral ligament also requires knowledge of the varied shape and signal intensity that this ligament can display.20

Carpal bones

MR imaging is sensitive and specific for evaluation of fracture. The most common indication in the wrist is for radiographically occult fractures of the scaphoid, and in this setting, an additional coronal fat suppression technique is required. Increased signal intensity on short tau inversion recovery (STIR) images and a well demarcated fracture line are seen in the scaphoid. MR imaging also is commonly used for evaluation of degree of collapse and marrow viability in patients with Kienbock's disease (figure 15). In both cases, associated injury or degeneration of adjacent cartilage can be assessed, which in turn influences decisions concerning wrist débridement, partial carpectomy, and fusion.

Carpal tunnel

Previously, MR imaging also was performed for evaluation of carpal tunnel syndrome. Recent reports, however, have demonstrated that most of the reported MR imaging signs of carpal tunnel syndrome are nonspecific, as they also have been found in asymptomatic volunteers.21 The more statistically significant signs of carpal tunnel syndrome include flexor retinacular bowing and flexor tenosynovitis.21 In symptomatic patients, compressive soft-tissue masses, such as ganglion cyst of the carpal tunnel (figure 16), tenosynovitis of the flexor tendon sheaths and, less likely, tumor of the median nerve, may be seen. In patients status post-carpal tunnel release with persistent symptoms, MRI also may disclose the relative integrity of the flexor retinaculum.

In conclusion, MR imaging of the elbow and wrist has been proven to accurately depict injuries to tendinous, ligamentous, and osseous structures, as well as to cartilage. MR imaging also is ideal for excluding other differential diagnoses of acute or chronic elbow and wrist pain. In many institutions, it has replaced triple phase arthrography in the initial work-up of wrist pain, as arthrograms may be negative in the presence of surgically-proven tears of the articular disc.22 AR

References

1. Stoller DW: MR Imaging in Orthopaedics and Sports Medicine, ed 2, pp 745-775. Philadelphia, Lippincott-Raven, 1997.

2. Gaary EA, Potter HG, Altchek DW: Medial elbow pain in the throwing athlete: MR imaging evaluation. AJR 168:795-800, 1997.

3. Morrey BF, An AKN: Articular and ligamentous contribution to the stability of the elbow joint. Am J Sports Med 11:315-319, 1983.

4. Cotten A, Jacobson J, Brossman J, et al: Collateral ligaments of the elbow: Conventional MR imaging and MR arthrography with coronal oblique plane and elbow flexion. Radiology 204(3):806-812, 1997.

5. Potter HG, Hannafin JA, Morwessel RM, et al: Lateral epicondylitis: Correlation of MR imaging, surgical and histopathologic findings. Radiology 196(1):43-46, 1995.

6. Nirschl RP, Pettrome FA: Tennis elbow: The surgical treatment of lateral epicondylitis. J Bone Joint Surg (AM) 61:832-839, 1979.

7. Mirowitz SA, London SL: Ulnar collateral ligament injury in baseball pitchers: MR imaging evaluation. Radiology 185:573-576, 1992.

8. Rosenberg ZS, Beltran J, Cheung YY: Pseudodefect of the capitellum: A potential MR imaging pitfall. Radiology 191:821-823, 1994.

9. O'Driscoll SW, Morrey BF: Lateral collateral ligament injury. In: Morrey BF (ed): The Elbow and its Disorders, pp 573-580. Philadelphia, WB Saunders, 1993.

10. Potter HG, Weiland AJ, Schatz JA, et al: Posterolateral rotatory instability of the elbow: Usefulness of MR imaging in diagnosis. Radiology 204:185-189, 1997.

11. Totterman SMS, Miller RJ: Triangular fibrocartilage complex: Normal appearance on coronal three-dimensional gradient-recalled-echo MR images. Radiology 195:521-527, 1995.

12. Oneson SR, Scales LM, Timins ME, et al: MR imaging interpretation of the palmer classification of triangular fibrocartilage complex lesions. Radiographics 16:97-106, 1996.

13. Palmer AK: Triangular fibrocartilage complex lesions: A classification. J Hand Surg (AM) 14:594-605, 1989.

14. Oneson SR, Timins ME, Scales LM, et al: MR imaging diagnosis of triangular fibrocartilage pathology with correlation. AJR 168:1513-1518, 1997.

15. Totterman SMS, Miller RS, McCance SE, Myers SP: Lesions of the triangular fibrocartilage complex: MR findings with a three-dimensional gradient-recalled-echo sequence. Radiology 199:227-232, 1996.

16. Potter HG, Asnis-Ernberg L, Weiland AJ, et al: The utility of high resolution magnetic resonance imaging in the evaluation of the triangular fibrocartilage complex of the wrist. J Bone Joint Surg 79(A):1675-1684, 1997.

17. Bednar MS, Arnoczky SP Weiland AS: The microvasculature of the triangular fibrocartilage complex: Its clinical significance. J Hand Surg (AM) 10:1101-1105, 1991.

18. Totterman SMS, Miller RJ: Scapholunate ligament: Normal MR appearance on three-dimensional gradient-recalled-echo images. Radiology 200:237-241, 1996.

19. Mayfield JK: Pathogenesis of wrist ligament instability. In: Lichtman DM (ed): The wrist and its disorders, pp 53-73. Philadelphia, WB Saunders, 1988.

20. Smith DK, Snearly WN: Lunotriquetral interosseous ligament of the wrist: MR appearances in asymptomatic volunteers and arthrographically normal wrists. Radiology 191:199-202, 1994.

21. Radack DM, Schweitzer ME, Taras J: Carpal tunnel syndrome: Are the MR findings a result of population selection bias? AJR 169:1649-1653, 1997.

22. Chung KC, Zimmerman NB, Travis NT: Wrist arthrography versus arthroscopy: A comparative study of 150 cases. J Hand Surg 21A:591-594, 1996.

Dr. Decker is a fellow in Musculoskeletal Radiology at the Hospital of Special Surgery in New York, NY, where Dr. Potter is Chief of the MRI Division.

Dr. Potter is also Associate Professor of Radiology at Cornell University Medical College in New York, NY.