Supinator muscle

Origin and insertion

The wide supinator muscle consists of superficial and deep layers. These layers differ only in their mode of attachment; the superficial layer arises by tendinous fibers, while the deep layer originates with already formed muscular slips.

Both layers originate from the same landmarks. These involve several osteofibrous structures of the elbow; lateral epicondyle of humerus, radial collateral ligament of humeroulnar joint, annular ligament of the superior radioulnar joint, supinator crest of ulna and the adjacent part of ulnar fossa.

From here the muscle wraps (spirals) around the proximal third of the radius, inserting to the upper third of its lateral, posterior and anterior surfaces.

Relations

Supinator is found deep in the forearm, superficial only to the parts of the radius and ulna over which the muscle lies. Along with the brachialis muscle, it forms the floor of the cubital fossa. Extensor carpi radialis brevis and longus cover the muslce’s radial surface, while the inferior part of the anconeus muscle overlies it from the ulnar side.

The deep branch of the radial nerve gives off the posterior interosseous nerve just proximal to the supinator muscle. The nerve then passes between the muscle’s superficial and deep heads to enter the extensor compartment of the forearm. Sometimes an inconsistent fascial band called the oblique cord passes over the deep head of supinator. The cord connects the radius and ulna by extending between the ulnar and radial tuberosities.

Innervation

Supinator is innervated by the posterior interosseous nerve (C7, C8), a branch of the radial nerve.

Why not take a breather and test what you've already learned about the supinator muscle and the other muscles of the posterior compartment?

Blood supply

The superficial and deep layers of the supinator muscle are supplied by two different sources;

• Superficial layer receives blood from the radial artery, via its radial recurrent branch
• Deep layer is supplied by the ulnar artery, through its posterior interosseous and posterior interosseous recurrent arteries

Function

Supinator muscle rotates the radius laterally at the proximal radioulnar joint. This action puts the radius parallel to the ulna, therefore bringing the hand into the supine position (facing anteriorly, palm up, like holding a bowl of soup).

When producing a slow and unopposed supination movement, the supinator muscle suffices on its own, and is the prime mover. An example of such a movement is the simple rotation of the hand when grabbing popcorn from a bowl.However, for a quick, strong, forceful supination movement, or when the movement happens against resistance, the supinator muscle is assisted by the biceps brachii muscle. Note that biceps brachii cannot act as a supinator when the forearm is fully extended, so the most powerful supination occurs when the elbow joint is flexed to 90 degrees. This action is seen, for example, when turning a screwdriver or pulling out the cork from a bottle of wine.