Interosseousnerven

Interosseousnerven, or interosseous nerves, refers to two motor nerves in the forearm: the anterior interosseous nerve (AIN) and the posterior interosseous nerve (PIN). The AIN is a branch of the median nerve in the proximal forearm and runs on the surface of the interosseous membrane. The PIN is the continuation of the deep branch of the radial nerve after it passes through the supinator. Both nerves are primarily motor and carry little to no cutaneous sensation.

The anterior interosseous nerve supplies the deep flexor group: flexor pollicis longus, the lateral part of the flexor digitorum profundus (to digits 2 and 3), and the pronator quadratus. It has no sensory function.

The posterior interosseous nerve supplies most of the extensor muscles in the posterior forearm, including extensor digitorum, extensor indicis, extensor digiti minimi, extensor carpi ulnaris, and the thumb extensors (extensor pollicis longus and brevis) as well as the abductor pollicis longus. It provides little to no cutaneous innervation.

Clinical relevance: injury or entrapment of the AIN causes anterior interosseous syndrome, characterized by weakness of FPL and FDP to digits 2–3 and pronator quadratus, with preserved sensation. The pinch test (the “OK” sign) is often impaired. PIN syndrome results in loss of finger and thumb extension, producing a finger drop; wrist extension may be weakened but sensation is typically intact. Etiologies include compression by fibrous bands, such as the arcade of Frohse, or other proximal nerve compression. Diagnosis is clinical, supported by electrodiagnostic studies and imaging. Treatment ranges from observation to surgical decompression or reconstruction based on severity and duration.