Transverse humeral ligament: does it exist?
The insertion of the tendon of subscapularis is accepted as being on the lesser tubercle of the humerus. The transverse humeral ligament (THL) is described as a distinct entity in most textbooks, overlying the long tendon of biceps as it emerges from the capsule of the shoulder joint. In this study, we dissected 85 embalmed shoulders to clarify the anatomy of the THL and variation in the insertion of the tendon of subscapularis. In all specimens no distinct THL could be identified, but in every shoulder a fibrous expansion arose from the posterior lamina of the tendon of pectoralis major overlying the long tendon of biceps. In 86% of shoulders, fibres from the tendon of subscapularis passed over the long tendon of biceps within this fibrous expansion and inserted on to the greater tubercle of the humerus where one would expect to find the THL. In 33% of dissections, fibres from the tendon of subscapularis lay deep to the long tendon of biceps, inserting either into the bicipital groove or on to the greater tubercle. In only 8% of cases did the tendon of subscapularis insert exclusively on to the lesser tubercle. We conclude that the THL does not exist as a separate entity. We suggest that in the majority of cases, the structure overlying the long tendon of biceps as it emerges from the capsule of the shoulder joint consists of tendinous fibres from subscapularis, contained within a fibrous expansion derived from the posterior lamina of the tendon of pectoralis major. In the minority of shoulders, where the tendon of subscapularis inserts exclusively on to the lesser tubercle, we hypothesise that this fibrous expansion acts as a retinaculum preventing the long tendon of biceps from "bowstringing."