Supraspinatus muscle

The supraspinatus is an intrinsic shoulder muscle located in the supraspinous fossa of the scapula that extends to the proximal humerus. It acts primarily in extension and stabilization of the shoulder joint.

Origin: Entire surface of the supraspinous fossa, including the spine of the scapula, and from the edge of the neck of the scapula.

Insertion: Greater tubercle of the humerus.

Action: Extension of the shoulder joint and advancement of the limb.

Antagonist: Shoulder flexors, primarily the deltoideus and teres major.

Vascularization: Supplied mainly by the suprascapular artery; venous drainage parallels arterial supply.

Nerve: Suprascapularis.

The supraspinatus arises from the entire supraspinous fossa, including the scapular spine and neck, forming a thick, fan-shaped muscle. Its fibers converge laterally to insert on the greater tubercle of the humerus. Functionally, it extends the shoulder and provides dynamic stabilization during locomotion. It is cranial to the infraspinatus, deep to the trapezius, and dorsal to the shoulder joint capsule. The arterial supply is mainly via the suprascapular artery, and the muscle is innervated by the suprascapular nerve. In comparison to humans, the canine supraspinatus is relatively more robust and has a larger role in weight-bearing stabilization.

Variations:

• In ruminants, the supraspinatus is less dominant than the infraspinatus, and its tendon inserts independently on the humerus. This arrangement supports a stabilizing role in the weight-bearing limb, which has a more limited range of motion compared to primates.

• In horses, the muscle inserts on both the greater (lateral) and lesser (medial) tubercles of the humerus. Its primary function is shoulder stabilization rather than force generation for extension, with the biceps brachii playing the key role in the passive stay apparatus.

• In domestic carnivores (dogs), the supraspinatus is proportionally smaller than the subscapularis. Its tendon inserts independently on the humerus.

• The human supraspinatus differs anatomically from that of quadrupeds because it is relatively smaller and composed of shorter fibers, reflecting the non–weight-bearing function of the upper limb and the need for a wide range of motion rather than forceful shoulder stabilization.