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Supinator muscle

Attachments, innervation and function of the supinator muscle.

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Hello again everyone! It's Matt from Kenhub, and in this tutorial, we will be discussing the supinator muscle.

The supinator muscle is one of the deep extensors of the forearm. The deep extensors of the forearm consist of five muscles located at the posterior side of the forearm namely supinator muscle, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, extensor indicis. Their muscle bellies and tendons form the surface of the distal forearm and the wrist where they can be easily palpated. As mentioned before, the focus of this tutorial is the supinator muscle.

The supinator muscle has a complex origin tendon arising from the lateral epicondyle of the humerus – the superficial part – and the supinator crest of the ulna – deep part. Furthermore, it also attaches to the radial collateral ligament and radial annular ligament. From there, the muscle curls dorsally around the neck of the radius and inserts laterally between the radial tuberosity and the insertion of the pronator teres.

Like all extensors of the forearm, these five muscles are innervated by the radial nerve. The radial nerve divides into a superficial branch and deep branch at the height of the radial head. While the superficial branch runs along the brachioradialis, the deep branch continues between the two layers of the supinator. It continues on to penetrate the supinator muscle and branches off as the posterior interosseus nerve, which is responsible for the innervation of almost all deep extensors. The supinator is the only deep extensor that receives supply directly from motor branches of the radial nerve.

The supinator works differently to the other deep extensors which main functions are to move the joints of the hands and the fingers. In contrast, the function of the supinator is to pull the radius causing a lateral rotation or supination at the radioulnar joints, hence, the title, supinator.

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