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Nerve Forearm

Posterior Interosseous Nerve at the Arcade of Frohse

nervus interosseus posterior ad arcadem Froehse

The posterior interosseous nerve (deep branch of the radial nerve) enters the posterior forearm by passing beneath the arcade of Frohse, the tendinous proximal arch of the supinator muscle. This is the most common site of posterior interosseous nerve entrapment, where the fibrous arch compresses the nerve against the radial head.

Region: Forearm

Clinical Relevance

Clinical Notes

Posterior interosseous nerve syndrome at the arcade of Frohse produces weakness of finger and thumb extension without sensory loss, distinguishing it from radial nerve palsy at the spiral groove. The condition is provoked by resisted supination and reproduced by deep palpation 4 cm distal to the lateral epicondyle. Surgical decompression involves release of the arcade of Frohse and the leading edge of the supinator. Electrodiagnostic studies confirm denervation in the extensor digitorum, extensor indicis, and APL while sparing the radial wrist extensors (which branch before the arcade).

Pathology

Common Injuries & Conditions

Posterior Interosseous Nerve Syndrome

Entrapment at the arcade of Frohse producing painless finger and thumb extensor weakness without wrist drop or sensory loss, confirmed by EMG showing denervation distal to the radial wrist extensors.

Radial Tunnel Syndrome

Pain-dominant variant of posterior interosseous nerve compression at the arcade of Frohse without measurable weakness, producing lateral forearm aching reproduced by resisted supination and middle finger extension.