Subscapularis Tendon Tear: An Anatomic and Clinical Investigation

Purpose: The purpose of this study was to clarify anatomically and clinically how the subscapularis tendon supports the superior portion of the biceps tendon to the intertubercular groove. Methods: Thirty-three embalmed shoulder girdles were examined to investigate the subscapularis tendon and the pathway of the biceps tendon. In addition, operation records of 435 consecutive arthroscopic rotator cuff repairs were retrospectively reviewed. Results: Anatomically, the superior-most insertion of the subscapularis tendon was located on the upper margin of the lesser tuberosity. In addition, a thin tendinous slip extended from the insertion and attached to the fovea capitis of the humerus. The insertion, the tendinous slip, and the lateral portion of the cranial part of intramuscular tendons were in direct contact with the inferior side of the biceps tendon at its corner portion. The clinical study showed that 27.4% of rotator cuff tears (119/435) had subscapularis tendon tears. In cases with an unstable biceps tendon there was no intact subscapularis tendon. The superior-most insertion of the subscapularis tendon was involved in all transverse tears. Of 29 full-thickness transverse tears, 13 (44.8%) showed intra-articular dislocation. Conclusions: The trochlea-like structure was composed of the superior-most insertion, the tendinous slip, and the lateral portion of the cranial part of intramuscular tendons supporting the biceps tendon. The transverse tear of the subscapularis tendon, which included this trochlea-like structure, often leads to intra-articular dislocation of the biceps tendon. Clinical Relevance: Instability of the biceps tendon should be carefully assessed because it is associated with subscapularis tendon tears at a very high incidence. When we repair a transverse tear of the subscapularis tendon, we should widely fix sufficiently strong tissue to support the biceps tendon on the uppermost margin, not on the anteromedial portion, of the lesser tuberosity.