Supinator

At a glance

English

Supinator

Latin (TA2)

Supinator

System

Muscle

Region

Upper limb

Side

Paired, left and right

About the supinator

Supinator lies deep among the extensor-side muscles of the forearm, just below the elbow, where it curls like a cuff around the radius's upper third. Its job is in its name: it turns the forearm so that the palm faces forwards or upwards, the movement called supination.

The muscle is built in two sheets, a superficial and a deep layer, and the radial nerve's deep branch runs between them. Both sheets start together from the lateral epicondyle of the humerus, the radial collateral and annular ligaments of the elbow, and the supinator crest and fossa of the ulna. The superficial layer begins as tendon and the deep one as fleshy fibres. They wind backwards and then forwards around the bone to attach on the lateral, posterior and anterior faces of the upper radial shaft, down to the level where pronator teres attaches.

Because it wraps the radius, supinator can rotate the bone whatever the angle of the elbow. Biceps brachii is the stronger supinator but works well only with the elbow bent; with the elbow straight, or when the movement is slow and unloaded, supinator does most of the work. Biceps joins in as the load grows.

The upper edge of the superficial layer forms a fibrous arch, the arcade of Frohse, under which the deep radial nerve enters the muscle. On leaving the lower border the nerve continues as the posterior interosseous nerve. Pressure at the arch, from a swelling or from repeated forearm rotation, can trap the nerve and weaken the finger and thumb extensors without loss of skin sensation, a picture called supinator or posterior interosseous nerve syndrome.

Attachments, action and supply

Origin

Lateral epicondyle of the humerus, radial collateral and annular ligaments of the elbow, and the supinator crest and fossa of the ulna.

Insertion

Lateral, posterior and anterior surfaces of the radius in its upper third, above the attachment of pronator teres.

Action

Supinates the forearm, in any position of the elbow.

Nerve supply

Radial nerve, deep branch, becoming the posterior interosseous nerve (C5, C6).

Blood supply

Radial recurrent artery, recurrent interosseous artery and branches of the posterior interosseous artery.