The supinator wraps around the proximal radius and is the primary supinator of the forearm, most dominant at slow speeds and light loads when the biceps brachii has not been recruited for its supination contribution. The deep branch of the radial nerve, after becoming the posterior interosseous nerve, passes through the radial tunnel between the two heads of the supinator, making this muscle the key structure in posterior interosseous nerve syndrome.
| Origin | Lateral epicondyle, radial collateral ligament, and annular ligament; Supinator crest of the ulna |
|---|---|
| Insertion | Posterior, lateral, and anterior surfaces of the proximal radius between the radial head and the pronator teres insertion |
| Nerve Supply | Deep branch of the radial nerve (posterior interosseous nerve) (C6) |
| Blood Supply | Radial recurrent artery |
| Actions | Supination of the forearm at all speeds and loads; No effect on elbow flexion |
|---|
It supinates the forearm through all ranges of elbow flexion without contributing to elbow movement, distinguishing it from the biceps brachii which supinates most effectively with the elbow flexed. It is the dominant supinator when precision rather than power is required.
Posterior interosseous nerve syndrome, where the deep radial nerve is compressed within the supinator muscle, produces motor weakness of the finger and wrist extensors without sensory loss, because the sensory branch of the radial nerve has already departed at this level. This differentiates it from a more proximal radial nerve palsy which produces both motor and sensory deficits. The syndrome is associated with repetitive forceful supination, lipomas within the radial tunnel, and rheumatoid synovitis at the radial head.
The supinator is not easily palpated directly as it lies deep to the brachioradialis and ECRL, but its activity can be assessed by applying resistance to forearm supination with the elbow extended, which eliminates the biceps contribution.
Compression of the deep radial nerve within the supinator producing wrist and finger extensor weakness without sensory loss, associated with repetitive supination activities and mass lesions within the radial tunnel.
