Upper limb

Tendon sheath of fifth extensor compartment (EDM)

Vagina tendinis musculi extensoris digiti minimi

Origin

Fifth dorsal compartment situated directly over the distal radioulnar joint (DRUJ)

Insertion

Encloses the tendon of extensor digiti minimi extending to the fifth digit extensor expansion

Function

Ensures low-friction gliding of the independent small finger extensor across the DRUJ

Innervation

Posterior interosseous nerve (C7–C8)

Movement & chain

Active during isolated fifth finger extension (pointing/piano playing)

Palpation

Palpable immediately dorsal to the distal radioulnar joint

Clinical

First tendon vulnerable to attrition rupture over a prominent scalloped ulnar head in rheumatoid arthritis (Vaughan-Jackson syndrome)

Segmental innervation

C7–C8 spinal segments

In clinical practice

Clinical testing of isolated small finger extension; surgical synovectomy and Darrach/Sauvé-Kapandji procedure when indicated

Region in the model

Upper limb