Extensor Retinaculum Third Compartment

vagina tendinum musculi extensoris pollicis longi

The third extensor compartment contains the extensor pollicis longus tendon, using Lister tubercle as its pulley to redirect the EPL around the dorsal wrist to reach the thumb. The EPL makes a 45-degree angle around the tubercle.

Anatomical Data

Boundaries & Contents

Location	Dorsal wrist, on the ulnar side of Lister tubercle
Boundaries	Floor: groove on the dorsal radius ulnar to Lister tubercle Roof: extensor retinaculum Lister tubercle forms its radial wall
Contents	Extensor pollicis longus tendon Synovial sheath

Biomechanics

Function & Actions

Uses Lister tubercle as a pulley to redirect the EPL tendon toward the thumb; the tendon can rupture here after distal radius fractures.

Clinical Relevance

Clinical Notes

EPL tendon rupture at the third compartment from Lister tubercle attrition is the classic late complication of minimally displaced distal radius fractures. EIP to EPL transfer is the standard reconstruction. The third compartment is released in EPL tendinitis and in distal radius arthroplasty approaches.

Pathology

Common Injuries & Conditions

EPL Rupture at Lister Tubercle

Late EPL attrition rupture over a sharp Lister tubercle edge after distal radius fracture, producing drop thumb treated by EIP tendon transfer.

Third Compartment Release in EPL Tendinitis

Decompression of the EPL within the third extensor compartment for inflammatory tenosynovitis producing dorsal wrist pain with thumb extension.

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