Supraspinatus fills snugly the whole of the supraspinous fossa of the scapula. It arises from the medial three-fourths of the fossa and from the upper surface of the scapular spine. It is bipennate, an arrangement that gives this bulky muscle great force of pull. A bursa separates it from the lateral fourth of the fossa. The tendon develops deep to the muscle as it crosses the superior part of the capsule of the shoulder joint; the two become blended together, to the great advantage of the capsule. The tendon passes on to be inserted into the smooth facet on the upper part of the greater tuberosity.
Nerve supply of supraspinatus:
By the suprascapular nerve (C5, 6), branching from the upper trunk of the brachial plexus which passes beneath the transverse ligament of the scapula and supplies the muscle by two branches.
Action of supraspinatus:
The muscle is of primary importance in bracing the head of the humerus to the glenoid fossa, to give stability during the action of other muscles, especially the deltoid, which it assists in abduction at the shoulder joint.