Summary
Origins
- Lateral epicondyle of the 🦴 humerus and the radial collateral ligament
- annular of the radius
- Supinator crest and fossa of the proximal 🦴 ulna
Insertions
- Lateral proximal third of the 🦴 radius between the neck and the pronator teres insertion
Actions
- Supinates the forearm, especially from a flexed position
The supinator wraps around the proximal radius like a broad band just below the elbow. Superficial fibers arise from the lateral epicondyle, radial collateral ligament, and crest of the ulna, while deep fibers originate from the supinator fossa and annular ligament. Together they spiral to the lateral surface of the radius, pulling it back into supination. The fibers dive beneath the extensor carpi radialis brevis, so layering the forms suggests the depth of the extensor mass.
The posterior interosseous branch of the radial nerve threads between the superficial and deep layers, so swelling of the muscle can mimic nerve injury in figures. biceps provides powerful supination when the elbow bends, while the supinator maintains the palm-up posture when the elbow is extended. pronator teres and pronator quadratus counter its action, and brachioradialis helps steady the radius during rapid rotation.