An anatomic study of the subscapularis insertion to the humerus: the subscapularis footprint.

PURPOSE: The purpose of this study was to elucidate the morphology of the subscapularis insertion into the humerus.
METHODS: Using 40 cadaveric shoulders from 12 men and 8 women (mean age, 91 years), we measured the maximum longitudinal (superior-to-inferior direction) and transverse (medial-to-lateral direction) length of the subscapularis insertion. The size of the bare area between the articular cartilage edge and the most medial tendon insertion at the proximal end, at the maximum transverse distance, and at the distal end was also measured.
RESULTS: In all cadavers the subscapularis insertion consisted of a proximal tendinous part and a distal muscular part. The mean longitudinal and transverse length of the insertion was 39.5 mm (SD, 6.7 mm) and 16.0 mm (SD, 2.2 mm), respectively. The mean longitudinal length of the tendon part was 26.3 mm (SD, 2.3 mm). The mean size of the bare area at the proximal end, at the maximum transverse distance, and at the distal end was 3.2 mm (SD, 1.7 mm), 6.5 mm (SD, 1.8 mm), and 16.8 mm (SD, 7.1 mm), respectively. The longitudinal and transverse length of the insertion and the size of the bare area at the maximum transverse distance and the distal end position were significantly greater in male specimens than in female specimens (P < .05). None of the measurements differed significantly on different sides.
CONCLUSIONS: The subscapularis footprint was broad proximally and tapered distally, exhibiting a comma shape. It consisted of a proximal tendinous part and a distal muscular part. With the exception of the bare area at the proximal end, the measured values were significantly larger in male specimens than in female specimens. CLINICAL RELEVANCE: The precise anatomic measurements presented here are useful for the evaluation and repair of tears of the subscapularis.