Posterior Compartment of the Forearm
Posterior compartment of forearm contains the extensor muscles innervated by the radial nerve.
The posterior compartment of the forearm is also called the extensor-supinator compartment. It contains muscles that primarily extend the wrist and fingers and supinate the forearm. These muscles are innervated by the radial nerve (deep branch or posterior interosseous nerve) and receive blood from the posterior interosseous artery.
Boundaries
| Structure | Description |
|---|---|
| Anterior | Radius, ulna, interosseous membrane |
| Posterior | Antebrachial fascia and skin |
| Medial & Lateral | Intermuscular septa separating it from anterior compartment |
Muscle Layers
It consists of a superficial layer and a deep layer.
Superficial Layer (7 Muscles)
| Muscle | Origin | Insertion | Innervation | Function |
|---|---|---|---|---|
| Brachioradialis | Lateral supracondylar ridge | Styloid process of radius | Radial nerve | Flexes elbow (despite being in extensor group) |
| Extensor carpi radialis longus | Lateral supracondylar ridge | Base of 2nd metacarpal | Radial nerve | Wrist extension, radial deviation |
| Extensor carpi radialis brevis | Lateral epicondyle of humerus | Base of 3rd metacarpal | Deep branch of radial nerve | Wrist extension, radial deviation |
| Extensor digitorum | Lateral epicondyle of humerus | Extensor expansions of digits 2–5 | Posterior interosseous nerve | Extension of fingers at MCP and IP joints |
| Extensor digiti minimi | Lateral epicondyle of humerus | Extensor expansion of digit 5 | Posterior interosseous nerve | Extension of little finger |
| Extensor carpi ulnaris | Lateral epicondyle and ulna | Base of 5th metacarpal | Posterior interosseous nerve | Wrist extension and ulnar deviation |
| Anconeus | Lateral epicondyle | Lateral olecranon and posterior ulna | Radial nerve | Assists in elbow extension and stabilization |
Deep Layer (5 Muscles)
| Muscle | Origin | Insertion | Innervation | Function |
|---|---|---|---|---|
| Supinator | Lateral epicondyle, ulna | Proximal radius | Deep branch of radial nerve | Forearm supination |
| Abductor pollicis longus | Ulna, radius, interosseous membrane | Base of 1st metacarpal | Posterior interosseous nerve | Abduction of thumb at CMC joint |
| Extensor pollicis brevis | Radius and interosseous membrane | Base of proximal phalanx of thumb | Posterior interosseous nerve | Extension of thumb at MCP joint |
| Extensor pollicis longus | Ulna and interosseous membrane | Base of distal phalanx of thumb | Posterior interosseous nerve | Extension of thumb at IP joint |
| Extensor indicis | Ulna and interosseous membrane | Extensor expansion of index finger | Posterior interosseous nerve | Extension of index finger |
Contents
- Radial nerve: Supplies brachioradialis, ECRL, and divides into deep (motor) and superficial (sensory) branches
- Posterior interosseous nerve: Continuation of deep branch; supplies most extensors
- Posterior interosseous artery: Branch of ulnar artery (via common interosseous artery)
Function
- Wrist Extension: ECRL, ECRB, ECU
- Finger Extension: Extensor digitorum, EDM, EI
- Thumb Extension: EPL, EPB; Thumb Abduction: APL
- Forearm Supination: Supinator
Surface Anatomy
The tendons of extensor muscles (especially EPL and APL) form the borders of the anatomical snuffbox. The extensor tendons become visible on the dorsum of the hand and wrist during finger extension.
Clinical Significance
- Lateral Epicondylitis (Tennis Elbow): Overuse injury involving the common extensor origin
- Posterior Interosseous Nerve Syndrome: Motor neuropathy without sensory loss; caused by entrapment in the supinator (arcade of Frohse)
- Extensor Tendon Injuries: May result from trauma or lacerations, leading to loss of finger extension
- Wrist Drop: Radial nerve palsy causing inability to extend wrist or fingers
Comparative Anatomy
In quadrupeds, extensors are stronger for weight-bearing. In humans, they have adapted for coordinated wrist and finger movements essential for activities like typing, writing, and playing instruments.
Last updated on May 12, 2025
