Subscapularis minor-does it exist?

Abstract

Introduction: It has been well established that the subscapularis is divided in two different parts with a tendinous insertion at its superior two-thirds and a muscular attachment on its inferior third. The objective of this cadaveric study was to follow the muscular insertion of the subscapularis medially in order to determine the origin of this inferior muscle insertion and whether a subscapularis minor can be individualized MATERIALS AND METHODS: Twenty-six shoulders from thirteen fresh-frozen cadaveric specimens (5 males and 8 females; mean age, 74.4 years) were dissected in our anatomy lab. The humeral insertion of the subscapularis was then analyzed, and the inferior muscular part of the insertion was identified. The muscle fibers were followed medially until their scapular origin which was recorded as line drawings and photographs. We measured the dimensions of both the humeral insertion and of the scapular origin of the fibers going to the muscular portion.

Results: In all cases, the fibres going to the tendinous portion and those going to the muscular portion of the insertion had a different orientation. The fibres going to the muscular portion of the humeral insertion did not originate from the subscapularis fossa but on the glenoid neck and in a depression at the infero-lateral part of the scapular pillar. The mean length of the superior tendinous portion of the humeral insertion was 3.42 cm (± 0.43 cm); the mean length of the inferior muscular portion of the humeral insertion was 1.88 cm (± 0.80 cm). The mean length of the scapular origin in the depression at the infero-lateral part of the scapular pillar of the fibres going to the muscular portion of the humeral insertion was 3.7 cm (± 0.17 cm).

Conclusion: The fibres of the subscapularis do not all originate from the subscapularis fossa. An additional origin exists at the inferior part of the glenoid neck and in a depression at the infero-lateral part of the scapular pillar. The fibers which originate at this location all insert on the humerus at the muscular portion of the subscapularis humeral insertion. This portion however does not seem to correspond to the so-called subscapularis minor which has been previously described.

Keywords: Cadaveric study; Fatty infiltration; Irreparable subscapularis; Rotator cuff muscle; Subscapularis minor; Subscapularis muscle.