The drawing provides an anterior view of the course of the radial nerve at the elbow. Posterior interosseous nerve (PIN) entrapment may occur due to prominent radial recurrent artery (RRA), medial edge of the extensor carpi radialis brevis (ECRB), and proximal edge of the supinator muscle (SP) (arcade of Frohse). RN: radial nerve, SRN: superficial radial nerve.