SUPRASPINATUS FOOTPRINT: DOES THE ROTATOR CUFF INSERT BY HOOD MECHANISM?

Abstract

The rotator cuff is sited on the anatomical neck of the humerus and is formed by the insertion of the supraspinatus (SP), infraspinatus (IS), teres minor (TM) and subscapularis. All play a vital role in the movement of the glenohumeral joint, and the anatomy is of critical importance in arthroscopic rotator cuff repair. We undertook an osteological and gross anatomical dissection study of the insertion mechanism of these tendons, in particular the SP .

The SP inserts by a triple or quadruple mechanism. The ‘heel’ (medial) and capsule fuse, inserting into the anatomical neck proximal to the anterior facet of the greater humeral tubercle. The ‘foot arch’ inserts as a strong, flat, fibrous tendon into the facet. This area is cuboidal, rectangular, or ellipsoid, and measures 36 mm² to 64 mm². In about 5%, the insertion is fleshy (pitted), rendering it weaker than a tendinous attachment. The ‘toe’ lips over the edge of the facet laterally and fuses with the periosteum, fibres of the inter-transverse ligament and the IS. A proximal ‘hood’ of about 4 mm stretches down inferiorly and fuses with the periosteum of the humeral shaft. The subacromial or subdeltoid synovial bursa are sited laterally.

The IS and TM insert into the middle and posterior facets (225 mm and 36 mm²) at respective angles of 80° and 115°. The inferior portion of the TM facet is not fused with the shoulder capsule. The subscapularis inserts broadly into the lesser tubercle, and the superior fibres fuse with the shoulder capsule and intertransverse ligament. The insertion of the subscapularis does not contribute directly to the formation of the ‘hood’, which belongs exclusively to the SP, IP and TM.

This study confirms the complexity of the SP insertion and suggests that an unfavourable attachment or biomechanical anatomical malalignment may lead to eventual tendon/cuff degeneration.