Overview
The posterior interosseous nerve (PIN) originates as the deep branch of the radial nerve and emerges after traversing the supinator muscle, continuing its course along the posterior compartment of the forearm to innervate the extensor muscles.
Origin and Course
Origin
- The PIN arises from the radial nerve at the level of the radiohumeral joint.
- It is derived from C7 and C8 spinal nerve roots.
Course
- Passes through the radial tunnel.
- Enters the supinator muscle via the arcade of Frohse (fibrous band in the proximal part of the supinator).
- Emerges from the distal edge of supinator into the posterior compartment of the forearm.
- Travels along the posterior interosseous membrane alongside the posterior interosseous artery.
- Terminates in the distal forearm, supplying branches to the wrist joint and intercarpal ligaments.
Relations
Proximal Relations
- Lies deep to the brachioradialis and extensor carpi radialis longus (ECRL) before entering the radial tunnel.
- Crosses the radial head and enters the supinator muscle.
Mid-course Relations
- Deeply situated within the supinator muscle.
- Accompanied by the posterior interosseous artery.
Distal Relations
- Lies on the interosseous membrane between the extensor pollicis longus (EPL) and extensor indicis (EI) tendons.
- Terminates near the dorsal wrist capsule.
Branches
Muscular Branches
Supplies the extensors of the wrist and digits, including:
- Extensor carpi radialis brevis (ECRB)
- Supinator
- Extensor digitorum communis (EDC)
- Extensor digiti minimi (EDM)
- Extensor carpi ulnaris (ECU)
- Abductor pollicis longus (APL)
- Extensor pollicis brevis (EPB)
- Extensor pollicis longus (EPL)
- Extensor indicis (EI)
Articular Branches
- Provides small branches to the radiocarpal and intercarpal joints.
Variations
- The arcade of Frohse may be more fibrous in some individuals, affecting the course of the nerve.
- In some cases, the PIN may receive additional fibres from the median nerve.
- The terminal branch may communicate with the superficial branch of the radial nerve.