Applied Anatomy of the Extensor Retinaculum

De Quervain’s Tenosynovitis

Definition: Stenosing tenosynovitis of the tendons in compartment I of the extensor retinaculum — affecting abductor pollicis longus (APL) and extensor pollicis brevis (EPB).

Mechanism: Repeated friction of the tendons against the fibro-osseous tunnel in compartment I → inflammatory thickening of the tendon sheath → stenosis → painful restriction of movement.

Common in: New mothers (lifting baby), domestic workers, musicians — any activity involving repetitive thumb movement with ulnar deviation of the wrist.

Clinical Features:

• Pain and tenderness over the radial styloid and first compartment
• Swelling over the first compartment

Finkelstein’s test: Patient makes a fist with the thumb inside the fingers; examiner deviates the wrist ulnarly — produces sharp pain over compartment I. This is the diagnostic test for de Quervain’s tenosynovitis.

Treatment: Rest, NSAIDs, steroid injection into the tendon sheath, surgical release of compartment I (splitting the extensor retinaculum over the first compartment).

Intersection Syndrome

Definition: Tenosynovitis at the point where the tendons of compartment I (APL + EPB) cross over the tendons of compartment II (ECRL + ECRB) — approximately 4–6 cm proximal to the wrist.

Features: Pain, swelling, and crepitus (“squeaky leather”) over the dorsoradial forearm — proximal to the wrist (distinguishes it from de Quervain’s which is at the radial styloid)

Common in: Rowers, skiers, weight lifters

Rupture of Extensor Pollicis Longus

Mechanism: The tendon of EPL wraps around Lister’s tubercle (compartment III) — this creates a zone of relative ischaemia. Rupture may occur:

• After Colles’ fracture — even undisplaced — due to erosion against the fracture haematoma or irregularity of the bone
• In rheumatoid arthritis (synovitis of compartment III)
• Spontaneously (idiopathic)

Clinical feature: Loss of extension of the interphalangeal joint of the thumb (EPL extends IP joint; EPB only extends MCP joint) — patient cannot lift the thumb off a flat table (positive tabletop test)

Treatment: Tendon transfer (EI to EPL) — primary repair usually not possible due to poor vascularity.

Dorsal Wrist Ganglion

Definition: A cystic swelling arising from the dorsal wrist joint capsule or tendons, commonly over the scapholunate ligament.

Location: Most commonly appears at the dorsum of the wrist between compartments III and IV (over the scapholunate interval)

Features: Soft, transilluminable, fluctuant swelling — increases with wrist flexion (tense), decreases with extension

Treatment: Aspiration, surgical excision; significant recurrence rate

Colles’ Fracture — Dorsal Complications

A Colles’ fracture (transverse fracture of the distal radius with dorsal displacement and angulation) may cause:

• Rupture of EPL (as above) — delayed complication, weeks to months after the fracture
• Compartment syndrome — acute complication
• Malunion → compression of median nerve (carpal tunnel syndrome) or extensor tenosynovitis

Superficial Radial Nerve — Wartenberg’s Syndrome

The superficial branch of the radial nerve passes superficial to the extensor retinaculum (does not pass through any compartment). As it passes under the brachioradialis tendon and enters the dorsum:

• Entrapment at the brachioradialis tendon → Wartenberg’s syndrome
• Pain, numbness, and tingling over the dorsum of the thumb and first web space
• May mimic de Quervain’s tenosynovitis — distinguish by: Wartenberg’s has sensory symptoms, Finkelstein’s test negative

Posterior Interosseous Nerve in Compartment IV

The posterior interosseous nerve (deep branch of radial nerve) passes through compartment IV of the extensor retinaculum (with extensor digitorum and extensor indicis). At the wrist, the nerve terminates as a pseudoganglion on the posterior interosseous membrane and gives articular branches to the wrist and carpal joints.

This is a useful landmark — damage to structures within compartment IV may affect the terminal articular branches.