EPL is the only extensor of the thumb IP joint and forms the medial border of the anatomical snuffbox. Its unique course around Lister's tubercle makes it vulnerable to rupture here after distal radius fractures.
| Origin | Posterior ulnar shaft — middle third |
|---|---|
| Insertion | Base of the thumb distal phalanx — dorsal surface |
| Nerve Supply | Posterior interosseous nerve (C7, C8) |
| Blood Supply | Posterior interosseous artery |
| Actions | Extends the thumb IP joint — the only extensor of the thumb IP joint; Extends and adducts the thumb MCP joint; Radially deviates the wrist |
|---|
EPL rupture is a recognised late complication of non-displaced distal radius fractures, occurring 4-8 weeks post-injury from attrition over a sharp Lister's tubercle edge. EPL rupture produces inability to extend the thumb IP joint — the "dropped thumb" deformity. EIP transfer (index to thumb) is the standard reconstruction.
Tested by thumb IP extension — the only test for EPL function specifically.
Late EPL tendon rupture from Lister's tubercle attrition 4-8 weeks after seemingly minor distal radius fracture, reconstructed by EIP to EPL tendon transfer.
