These authors sought to characterize the histologic structure of the subscapularis tendon from its humeral insertion point to the musculotendinous junction in 10 autopsy samples. Histologic analysis revealed 2 fibrous layers, distinguishable by the orientation of the collagen bundles. The deep layer was thinner and composed of parallel longitudinal collagen fibers inserting onto the lesser tuberosity flush with the cartilage. The superficial layer was thicker and composed of interdigitated collagen bundles inserting onto the lesser and the greater tuberosity after splitting into 2 bands, 1 lining the floor of the bicipital groove, and the other extending over the long head of the biceps tendon across the groove. Each layer formed an independent musculotendinous junction in the subscapularis muscle.
Comment: Mother nature is obviously very serious about securing the subscapularis attachment to the humerus. While subscapularis tears can occur in the previously unoperated shoulder, subscapularis failure is most common after a prior surgery during which it was incised and repaired.
Subscapularis failure presents as weakness of elevation, difficulty pressing the hand into the chest, and increased external rotation.
Subscapularis failure can also result in anterior instability
Often the torn tendon is of poor quality, so that a strong re-repair is impossible.
In such cases, a braded hamstring allograft is used to reinforce the repair.
The graft is passed through holes created in the lesser tuberosity.
The two ends of the graft are then passed through the strongest part of the remaining subscapularis tendon.
The tendon graft is then folded back laterally and secured to the lesser tuberosity to reinforce the repair of the remaining subscapularis tendon.
With this method, strength and stability can often be restored.
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