Muscle · Shoulders

Supraspinatus

Musculus supraspinatus

A small muscle lying in the trough above the ridge of the shoulder blade, whose tendon passes through a narrow gap between the top of the arm bone and the bony roof above it before attaching. Two things follow from that. It is the muscle that starts the arm moving away from the side — the deltoid has almost no leverage in the first few degrees — and it is the tissue that gets squeezed in that gap, which makes it the most commonly injured muscle in the shoulder. Through the whole of elevation its real work is quieter: it presses the head of the arm bone into its socket so the deltoid's upward pull has something to rotate around.