Surgical Anatomy of the Rotator Cuff and the Natural History of Degenerative Periarthritis

The rotator cuff consists of four muscles. These are the subscapularis, the supraspinatus, the infraspinatus and the teres minor muscles. These muscles end in short, flat, broad tendons which fuse intimately with the fibrous capsule to form the musculotendinous cuff. This fusion occurs approximately 1⁄2 to inch from the point of the insertion of the tendons into the humerus. The subscapularis muscle is a large, flat structure arising from the subscapular fossa. Its tendon fibers blend with the fibrous capsule just lateral to the glenoid brim, and then this portion of the musculotendinous cuff inserts into the lesser tuberosity. In addition, some of the fibers of this muscle insert directly into the shaft of the humerus immediately below the tendinous insertion. Roughly, the volume and power of the subscapularis muscle is sufficient to oppose the volume and power of the infraspinatus and teres minor muscles posteriorly (Fig. 1). The infraspinatus muscle takes origin from the infraspinous fossa on the posterior aspect of the scapula, and its tendon together with the fibrous capsule inserts into the greater tuberosity. It is intimately associated both structurally and functionally with the teres minor muscle. It is innervated by the suprascapular nerve (Fig. 1). The teres minor muscle takes origin from the axillary border of the scapula, and its tendon together with the capsule inserts into the inferior facet of the greater tuberosity. Like those of the subscapularis muscle, some of its fibers insert directly into the humerus distal to its tendinous insertion. This muscle is innervated by a branch of the axillary nerve. The supraspinatus muscle takes origin in the supraspinous fossa, and after its tendon fuses with the capsular fibers, it inserts into the greater tuberosity just posterior to the bicipital groove (Fig. 1). At this point it should be noted that the supraspinatus, infraspinatus and teres minor muscles at their points of insertion cannot be separated into anatomic units. However, between the supraspinatus and subscapularis there is a definite interval which is occupied by the coracohumeral ligament. Also, through this interval the biceps tendon together with its synovial covering passes through the joint capsule. The supraspinatus muscle is innervated by the suprascapular nerve.