Origin Lateral epicondyle of humerus, radial collateral and annular ligaments, supinator fossa and crest of ulna Insertion Lateral, posterior and anterior surfaces of proximal 1/3 of radius Action Supinates forearm (i.e., rotates radius to turn palm anteriorly) Innervation Deep branch of radial nerve (C5 and C6) (C5, C6) Arterial Supply Recurrent interosseous artery Clinical conditions1. PIN Compression Syndrome