Upper limb

Supinator

Musculus supinator

Origin

Lateral epicondyle of the humerus and the supinator crest of the ulna

Insertion

Proximal lateral surface of the radius

Function

Supination of the forearm

Innervation

Deep branch of the radial nerve (C5–C7), which pierces the muscle

Movement & chain

The primary supinator with the elbow extended and without resistance; during forceful supination (such as tightening a screw), biceps brachii takes over most of the work.

Palpation

Difficult to isolate directly; lies deep around the proximal radius beneath the extensor muscles of the forearm.

Clinical

The deep branch of the radial nerve can become entrapped where it passes through the muscle (arcade of Frohse), leading to posterior interosseous nerve syndrome with loss of finger extension but no sensory loss.

Segmental innervation

C5–C7.

In clinical practice

The arcade of Frohse, where the deep branch of the radial nerve pierces the muscle, is a point of interest in posterior interosseous nerve syndrome and in surgical approaches to the proximal forearm.

Region in the model

Upper limb