Posterior Interosseous Nerve, Posterior View

Description

Seen from a posterior forearm perspective, the posterior interosseous nerve (deep branch of the radial nerve) courses deep to the extensor compartment and enters the supinator at the proximal radius, then emerges distally to travel along the posterior aspect of the interosseous membrane. Superficial and deep extensor groups frame the nerve, including extensor digitorum, extensor carpi ulnaris, extensor carpi radialis brevis, and the deep layer with abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis. The radius lies lateral and the ulna medial in anatomical position, with extensor tendons converging toward the dorsum of the wrist and hand. Dorsal metacarpals, phalanges, and extensor expansions anchor the distal relationships. Understanding the nerve’s penetration through the supinator matters because this is the classic site of compression in radial tunnel syndrome and posterior interosseous nerve syndrome. Motor deficits dominate, with weakness of finger and thumb extension and wrist extension often spared or only mildly weak because extensor carpi radialis longus receives innervation proximal to the lesion. This is a surgical landmark. A posterior view clarifies the arcade of Frohse at the supinator’s proximal edge and the nerve’s close relationship to extensor carpi radialis brevis, both relevant during decompression and during approaches to the proximal radius. Educators can drop this plate straight into upper limb anatomy labs, peripheral nerve teaching sessions, and exam preparation focused on radial nerve branches and extensor compartment organization. It also fits operative manuals, sports medicine texts, and patient-facing materials explaining why dorsal forearm pain can produce isolated finger drop without sensory loss. Anatomical accuracy verified by SciePro's Medical Advisory Board.