Supinator

The supinator is a broad, flat muscle located in the proximal forearm that encircles the upper third of the radius.

Origin

The supinator muscle arises from two distinct heads:

• Superficial (humeral) head: Originates from the lateral epicondyle of the humerus, the radial collateral ligament, and the annular ligament.

• Deep (ulnar) head: Arises from the supinator crest located on the posterolateral surface of the ulna.

Relationship with the radial nerve

The radial nerve undergoes bifurcation proximal to the supinator muscle. Its deep branch (which subsequently becomes the posterior interosseous nerve) passes through the interval between the superficial and deep heads of the muscle. This anatomical relationship is clinically significant as compression at this site can lead to posterior interosseous nerve syndrome.

Course and insertion

Following their respective origins, both muscle heads wrap around the posterior and lateral aspects of the radial head, neck, and proximal shaft. The combined muscle fibers insert onto the lateral surface of the radius, specifically in the area superior to the anterior oblique line and proximal to the pronator teres insertion site.