The extensor digiti minimi has a dedicated tendon to the little finger that passes through the fifth extensor compartment at the wrist, providing independent little finger extension without relying on the juncturae tendinum that would otherwise limit isolated extension. The Wartenberg sign of persistent little finger abduction in ulnar nerve palsy is partly produced by the intact EDM pull unopposed by the denervated palmar interosseous.
| Origin | Lateral epicondyle via the common extensor tendon |
|---|---|
| Insertion | Extensor expansion of the little finger via two slips |
| Nerve Supply | Posterior interosseous nerve (C7, C8) |
| Blood Supply | Posterior interosseous artery |
| Actions | Extension of the little finger MCP joint; Assists wrist extension |
|---|
Providing the little finger with its own extensor tendon distinct from the extensor digitorum allows the little finger to be extended independently during power grip when the other fingers are flexed, important for handling tools and instruments.
The EDM is tested by extending the little finger in isolation with the other fingers flexed. The fifth extensor compartment at the wrist, through which the EDM tendon passes, is a site of tenosynovitis in rheumatoid arthritis that can cause EDM tendon rupture by attrition. Wartenberg sign of resting little finger abduction is caused by EDM dominance over the weakened palmar interosseous in ulnar nerve palsy.
The EDM tendon is palpable on the dorsum of the little finger as the ulnar tendon at the MCP level, becoming distinct during isolated little finger extension.
Attrition rupture over the distal ulna in rheumatoid arthritis producing loss of little finger extension, managed with EDM repair or EIP tendon transfer.
