• Supinator supinates the forearm.
• The tendinous leading edge of the superficial head of the supinator constitutes the “Arcade of Frohse” and can compress the posterior interosseous nerve superficially.
Nerve Transfers: The supinator is a useful muscle for use as a nerve transfer donor as the biceps provides a significant component of supination; therefore the supinator can be sacrificed.
Muscle Function: Supinates the forearm.
Palpation: Lateral aspect of the forearm and on the proximal radius-quite deep and hard to palpate.
Strength Testing: Position – the subject in seated with elbow flexed to 90º, arm at the side, and forearm pronation to end-range. Stabilization – the forearm and with the wrist in neutral position. Resist – against supination of the forearm at the distal forearm in the direction of pronation.
Possible Substitutions: Muscles for wrist extension and lateral rotators of the shoulder. To prevent substitution by wrist extensors, keep the wrist in neutral. To prevent substitution by lateral rotations, stabilize the humerus against the trunk. In addition, biceps brachii can substitute for supination. To distinguish between the biceps brachii and supinator, compare strength of supination with the elbow flexed verses the elbow extended. If there is a difference in strength and noted greater weakness in elbow extended, this may indicate a weak supinator. Comparison to the uninvolved side would confirm this.
• The tendinous leading edge of the superficial head of the supinator is the “arcade of Frohse” and can compress the posterior interosseous nerve.
• Roots: C5, C6, (C7).
• Nerve: Radial nerve.
• Innervation Route: C5, C6, (C7) → radial nerve → supinator branch.
Origins: Lateral epicondyle of humerus, radial collateral ligament of elbow joint, annular ligament of radius, and supinator crest of ulna. The supinator consists of two planes of fibers: superficial plane and deep plane.
Insertion: Lateral surface of upper ⅓ of body of radius, both anterior and posterior surfaces.