Biceps Tendon Injury

Complete tears of the distal biceps are thought to be much more common than partial tears.45,46 MRI is useful in

Radialbicpital Bursa
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evaluating these injuries because degenerative tendino-sis, partial tears, and complete ruptures may be distin-guished.6,47,48

Distal biceps tendinosis is common and has been shown to precede spontaneous tendon rupture.13 Tendi-nosis of the distal biceps is probably a multifactorial process that involves repetitive mechanical impingement of a poorly vascularized distal segment of the tendon. Irregularity of the radial tuberosity and chronic inflammation of the adjacent radial bicipital bursa also may con-tribute.49,50 A zone of relatively poor blood supply exists within the distal biceps tendon approximately 10 mm from its insertion on the radial tuberosity.51 In addition, this hypovascular zone may be impinged between the radius and the ulna during pronation. The space between the radius and ulna progressively narrows by 50% during pronation, with average measurements of approxi-

FIGURE 4.10. Loose bodies in a professional pitcher with ulnar neuritis. A T1-weighted axial image distal to the medial epicondyle reveals an anterior compartment loose body (open arrow) and a posteromedial loose body (small white arrow) and thickened medial collateral ligament (curved arrow) that undermine the floor of the cubital tunnel adjacent to the ulnar nerve (black arrow).

FIGURE 4.10. Loose bodies in a professional pitcher with ulnar neuritis. A T1-weighted axial image distal to the medial epicondyle reveals an anterior compartment loose body (open arrow) and a posteromedial loose body (small white arrow) and thickened medial collateral ligament (curved arrow) that undermine the floor of the cubital tunnel adjacent to the ulnar nerve (black arrow).

mately 8 mm in supination, 6 mm in neutral position, and 4 mm in pronation recorded in asymptomatic volunteers with CT and MRI.51 Repetitive impingement during pronation coupled with an intrinsically poor blood supply of the distal biceps tendon may result in a failed healing response and degenerative tendinosis. Enlargement of the degenerated tendon and irregularity and hypertrophy of the radial tuberosity may lead to inflammation of the adjacent bursa. Each of these factors may contribute to worsening impingement between the radial tuberosity and the ulna, leading to further degeneration of the distal biceps tendon. Ultimately, this process may result in complete tendon rupture or, less commonly, partial tendon rupture or bursitis.

The distal biceps tendon is covered by an extrasynovial paratenon and is separated from the radial tuberos-ity by the bicipital radial bursa. Inflammation of this cubital bursa may accompany tendinosis and tearing of the distal biceps (Fig. 4.12). Enlargement of the bicipital radial bursa may occasionally present as a nonspecific antecubital fossa mass as large as 5 cm in diameter.50,52 Intravenous administration of gadolinium may aid in recognition of this enlarged bursa on MRI and may allow differentiation of this benign entity from a solid neo-plasm.52 Cubital bursitis, tendinosis, and partial tendon rupture may coexist to differing degrees and may be impossible to distinguish clinically.45,50 Cubital bursitis and partial tendon rupture may both cause irritation of the ad jacent median nerve, further complicating the clinical findings.50,53

The T2-weighted axial images are most useful for determining the degree of tendon tearing. These images also are useful for evaluating the lacertus fibrosus (Fig. 4.13). The axial images should extend from the musculotendi-nous junction to the insertion of the tendon on the radial tuberosity. MRI provides useful information regarding the degree of tearing, the size of the gap, and the location of the tear for preoperative planning. The tendon typically tears from its attachment on the radial tuberosity as a result of attempted elbow flexion against resistance.9 Rupture of the distal biceps tendon generally is treated with prompt surgical repair and reattachment to the radial tuberosity to restore flexion and supination strength. Early diagnosis of biceps tendon rupture is important because surgical outcome is improved in patients treated during the first several weeks after injury.54 After several months, the tendon retracts into the substance of the biceps muscle, making retrieval and reattachment more complicated. MRI may be useful in such cases to confirm the clinical diagnosis and to plan reconstructive surgery.

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