The EDM is the only finger extensor with its own dedicated compartment (fifth extensor compartment) separate from the other digits. This separate compartment allows truly independent little finger extension while the other fingers are flexed.
| Origin | Lateral epicondyle — common extensor origin |
|---|---|
| Insertion | Dorsal expansion of the little finger — via two slips to the extensor hood |
| Nerve Supply | Posterior interosseous nerve (C7, C8) |
| Blood Supply | Posterior interosseous artery |
| Actions | Extends the little finger MCP joint — independent extension separate from EDC; Assists wrist extension |
|---|
EDM tendon lacerations in zone 5 must be identified specifically — the double-slip insertion means both slips must be repaired. EDM tendon transfer to the ring finger is used in ring finger extension lag after EDC ring finger laceration with poor proximal tendon. The fifth extensor compartment is released in extensor tendon synovitis (rheumatoid arthritis).
Tested by resisted little finger MCP extension with all other fingers held in flexion.
Both slips of the extensor digiti minimi tendon must be repaired after zone 5 laceration to fully restore little finger MCP extension.
