Extensor Retinaculum Fourth Compartment

vagina tendinum musculorum extensorum digitorum et indicis

The fourth extensor compartment contains the extensor digitorum communis (four slips) and extensor indicis proprius tendons, forming the largest of the six compartments. It runs over the dorsal radius and wrist.

Anatomical Data

Boundaries & Contents

Location	Centre of the dorsal wrist, over the distal radius
Boundaries	Floor: dorsal surface of the distal radius ulnar to the third compartment Roof: extensor retinaculum
Contents	Four extensor digitorum tendons Extensor indicis tendon Posterior interosseous nerve and the terminal branch of the anterior interosseous artery on its floor

Biomechanics

Function & Actions

Holds the finger extensor tendons against the wrist so they do not bowstring when the wrist extends.

Clinical Relevance

Clinical Notes

Fourth compartment tenosynovitis in rheumatoid arthritis produces a characteristic dorsal wrist swelling that transmits with EDC tendon movement (extensor tenosynovitis sign). Rupture of EDC tendons in sequence (Vaughan-Jackson syndrome, ring finger first, then little, then middle) requires extensor tendon reconstruction.

Pathology

Common Injuries & Conditions

Rheumatoid Fourth Compartment Tenosynovitis

Pannus invasion of the fourth extensor compartment producing dorsal wrist swelling and progressive EDC tendon erosion, treated by synovectomy and tendon reconstruction for ruptures.

Vaughan-Jackson Syndrome, Sequential EDC Rupture

Progressive EDC tendon rupture from dorsal wrist synovitis beginning with the ring finger EDC, requiring urgent synovectomy and tendon transfer before further ruptures occur.

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