The relationship of the anterior articular capsule to the adjacent subscapularis: An anatomic and histological study

Introduction The purpose of this study was to delineate the anatomic relationship between the anterior articular capsule and the adjacent subscapularis by measuring the dimensions of the anterior articular capsule attachment and the subscapularis footprint on the humerus, as well as investigating the interface between the two structures. Materials and methods Three shoulder specimens underwent histological analysis; for histological analysis, cross-sections through the subscapularis-capsule complex were harvested at the tendinous and muscular insertion sites. The dimensions of the anterior articular capsule attachment and the subscapularis footprint (including the tendinous and muscular insertions) were measured in thirteen cadaveric shoulder specimens. Results Histologically, the articular capsule has thin and loosely arranged collagen fibers with many interspersing fibroblast nuclei, whereas the outer layer of the articular capsule blends into a layer of more loosely spaced and less organized collagen fibers. This interface between the subscapularis and the underlying articular capsule is filled with more loosely spaced and less organized collagen fibers. The macroscopic evaluation showed that the minimum articular capsule width (4.2 mm, SD 2.2 mm) was located at its initiation 4.9 mm (SD, 2.1 mm) inferior to the superior margin of the subscapularis; the corresponding subscapularis footprint width measured 10.1 mm (SD, 4.9 mm). The maximum articular capsule width was11.1 mm (SD, 3.7 mm) and was located 5 mm distal to the inferior margin of the tendinous footprint. The maximum subscapularis footprint width was 15.8 mm (SD, 2.9 mm); the corresponding articular capsule attachment measured 5.2 mm (SD, 1.8 mm). Conclusions Our results suggest that the anterior articular capsule attachment of the glenohumeral joint complements the footprint of the subscapularis and occupies a larger area of the lesser tubercle and metaphysis of the humerus than previously documented. The histological study confirms the presence of a demarcation between the subscapularis and articular capsule, specifically more significant at the region medial to the tendon insertion and at the muscular insertion of the subscapularis.