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F r e e S O A P n o t e s w i t h M a s s a g e B o o k f o r A B M P m e m b e r s : a b m p . u s / M a s s a g e b o o k 41 FUNCTIONAL ANATOMY education Supinator By Christy Cael The supinator muscle is located deep in the proximal posterior forearm. It lies deep to the brachioradialis and common extensor tendon at the lateral elbow. The supinator is a relatively flat muscle originating primarily on the dorsal surface of the proximal ulna, but also on the lateral epicondyle of the humerus, anterior fibers of the humeroulnar joint capsule, and proximal radioulnar ligament. The muscle wraps around the lateral surface of the radius, inserting broadly on the proximal radial surfaces, just distal to the radial head. Proximally, the supinator is divided into superficial and deep layers. This division creates a channel for the deep portion of the radial nerve, also known as the posterior interosseous branch. The tendon of the biceps brachii is also located near this Y-shaped portion of the supinator. Caution should be exercised when palpating the insertion of the biceps brachii and the fibers of the supinator to avoid compressing the radial nerve. When the supinator is activated, it rotates the radius posteriorly and laterally, supinating the forearm. It works synergistically with the biceps brachii and brachioradialis to supinate the forearm, turning the hand palm up. Unlike the biceps brachii, the supinator is strongest when the elbow is extending or extended. Some of its fibers attach to the lateral epicondyle of the humerus, allowing it to assist with this movement. The supinator reverses the action of the pronator teres and quadratus when turning a screwdriver or wrench. It is also activated when throwing a curveball in baseball. Here, the elbow extends while SUPINATOR Attachments • Origin: Lateral epicondyle of the humerus and supinator crest of the ulna • Insertion: Posterior, lateral, and anterior surfaces of proximal one-third of the radius Actions • Supinates the forearm • Slightly extends the elbow Innervation • Radial nerve • C5–T1 Supinator