The thumb extensor tendons form the anatomical snuffbox — the triangular hollow on the dorsoradial wrist between the EPL posteriorly and the APL and EPB anteriorly when the thumb is extended. The scaphoid can be palpated in the floor of the snuffbox and its tenderness in this position is a cardinal sign of scaphoid fracture. The EPL tendon around Lister tubercle is vulnerable to attrition rupture after minimally displaced distal radius fractures.
Thumb CMC extension and abduction (APL), MCP extension (EPB), IP extension (EPL); boundary tendons of the anatomical snuffbox
De Quervain tenosynovitis (APL and EPB in the first compartment) and EPL rupture (third compartment, around Lister tubercle) are the two primary pathologies of the thumb extensor tendons. The anatomical snuffbox scaphoid tenderness test has moderate sensitivity for scaphoid fractures but false negatives exist — MRI or CT should be performed when clinical suspicion is high despite normal radiographs.
EPL tendon disruption at Lister tubercle from distal radius fracture irregularity producing drooping thumb tip without trauma, managed with EI tendon transfer.
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