Oblique fibrous band; thickening of deep fascia on dorsum of wrist. Prevents bowstringing of extensor tendons during wrist extension.

Attachments

Oblique direction = lateral attachment on anterior (not posterior) border of radius.

Six Osseofibrous Compartments (Lateral → Medial)

Mnemonic (tendon count): 2, 2, 1, 2, 1, 1

Lister’s Tubercle

• Bony prominence on dorsal surface of lower radius
• Pulley for EPL tendon; separates compartments II (lateral) and III (medial)

Applied Anatomy

• De Quervain’s tenosynovitis — stenosing tenosynovitis of compartment I (APL + EPB); pain at radial styloid; Finkelstein’s test positive; Rx: rest, steroids, surgical release
• Intersection syndrome — tenosynovitis where compartment I crosses compartment II, ~4–6 cm proximal to wrist; common in rowers/skiers
• EPL rupture — attrition around Lister’s tubercle; after Colles’ fracture or RA; loss of IP extension of thumb; Rx: extensor indicis transfer
• Dorsal wrist ganglion — arises from dorsal capsule near scapholunate interval; between compartments III–IV; fluctuant swelling
• Wartenberg’s syndrome — superficial radial nerve entrapment beneath brachioradialis near wrist; pain + tingling over dorsoradial hand; no motor loss
• PIN in compartment IV — terminal articular branches of posterior interosseous nerve lie in floor; at risk in compartment IV surgery

Extensor Retinaculum — Definition and Attachments

Definition

The extensor retinaculum is an oblique fibrous band formed by thickening of the deep fascia on the dorsum (back) of the wrist.

It holds the extensor tendons in position as they cross the wrist joint and prevents them from bowstringing during wrist extension.

Orientation

• Directed downwards and medially as an oblique band
• Approximately 2 cm broad vertically
• Lies on the posterior aspect of the wrist, bridging the lower radius and ulna

Attachments

The lateral attachment to the anterior border of the radius, rather than the posterior border, accounts for the oblique direction of the retinaculum as it passes from anterolateral to posteromedial.

Deep Surface — Septa and Compartments

From its deep surface, the extensor retinaculum sends five septa downwards to the ridges on the dorsal aspects of the lower radius and ulna.

These septa divide the space deep to the retinaculum into six osseofibrous compartments, numbered I to VI from lateral (radial) to medial (ulnar).

Each compartment transmits one or more extensor tendons, with the tendons enclosed in synovial sheaths.

Functions

1. Prevents bowstringing of extensor tendons during wrist extension
2. Holds tendons in position on the dorsum of the wrist
3. Forms the roof of the osseofibrous compartments, with septa and bone forming the walls and floor
4. Reduces friction through synovial sheaths within the compartments

Comparison with Flexor Retinaculum

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Compartments of the Extensor Retinaculum

Overview

The space deep to the extensor retinaculum is divided into six osseofibrous compartments by five septa passing from the retinaculum to the dorsal surface of the radius and ulna.

Compartments are numbered I to VI from lateral (radial) to medial (ulnar).

Each compartment contains tendons enclosed in synovial sheaths that reduce friction.

The Six Compartments

Mnemonic for Compartment Contents (I–VI)

“2, 2, 1, 2, 1, 1” — number of main tendons in each compartment.

Or by content:

• I: APL + EPB → “APple” → thumb abductor + short thumb extensor
• II: ECRL + ECRB → two radial wrist extensors
• III: EPL → lone long thumb extensor, hooks around Lister’s tubercle
• IV: ED + EI → digit extensors, with terminal PIN and anterior interosseous artery deep
• V: EDM → little finger extensor
• VI: ECU → ulnar wrist extensor

Synovial Sheaths

Each compartment is lined by a synovial sheath extending approximately 2.5 cm proximal and 2.5 cm distal to the extensor retinaculum. The sheaths allow gliding of tendons within the osseofibrous tunnels.

Anatomical Snuff Box

The anatomical snuff box is a triangular depression on the radial side of the wrist, visible when the thumb is extended and abducted.

Boundaries:

Contents and superficial relations:

Clinical significance:

• Tenderness in the anatomical snuff box after a fall on the outstretched hand suggests fracture of scaphoid.
• The scaphoid receives important blood supply through vessels entering distally, so a waist fracture may cause avascular necrosis of the proximal pole.
• Scaphoid fractures may be missed on the initial X-ray; if clinical suspicion is high, immobilise and repeat imaging, or use MRI where available.

Lister’s Tubercle

The dorsal radial tubercle (Lister’s tubercle) is a bony prominence on the dorsal surface of the lower end of the radius:

• Acts as a pulley for the tendon of extensor pollicis longus
• Separates compartment II laterally from compartment III medially
• EPL passes medial to the tubercle and then turns laterally towards the thumb
• Serves as an important surgical and surface landmark on the dorsum of the wrist

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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 infants, domestic workers, musicians, and others with 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: The patient makes a fist with the thumb inside the fingers; the wrist is then deviated ulnarly. Sharp pain over compartment I supports de Quervain’s tenosynovitis.

Treatment: Rest, NSAIDs, steroid injection into the tendon sheath, and surgical release of compartment I when conservative treatment fails.

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 over the dorsoradial forearm, proximal to the wrist. This location helps distinguish it from de Quervain’s tenosynovitis, which is maximal near the radial styloid.

Common in: Rowers, skiers, weight lifters, and repetitive wrist-extension activities.

Rupture of Extensor Pollicis Longus

Mechanism: The tendon of EPL turns around Lister’s tubercle in compartment III, where it is vulnerable to attrition and relative ischaemia. Rupture may occur:

• After Colles’ fracture, even if undisplaced, due to attrition against callus, fracture irregularity, or local vascular compromise
• In rheumatoid arthritis due to synovitis of compartment III
• Occasionally spontaneously

Clinical feature: Loss of extension of the interphalangeal joint of the thumb. EPL extends the IP joint; EPB chiefly extends the MCP joint. The patient may be unable to lift the thumb off a flat table.

Treatment: Tendon transfer, commonly extensor indicis proprius to EPL; primary repair is often difficult because of attrition and poor tendon quality.

Dorsal Wrist Ganglion

Definition: A cystic swelling arising from the dorsal wrist joint capsule or tendon sheath, commonly related to the scapholunate interval.

Location: Most commonly appears on the dorsum of the wrist near the scapholunate ligament, often between compartments III and IV.

Features: Soft or tense fluctuant swelling that often becomes more prominent with wrist flexion.

Treatment: Observation, aspiration, or surgical excision; recurrence is common.

Colles’ Fracture — Dorsal Complications

A Colles’ fracture is a fracture of the distal radius with dorsal displacement and dorsal angulation of the distal fragment. Dorsal wrist complications may include:

• Delayed rupture of EPL, usually weeks to months after injury
• Extensor tenosynovitis from bony irregularity or malunion
• Median nerve compression / carpal tunnel syndrome, especially with swelling or malunion

Superficial Radial Nerve — Wartenberg’s Syndrome

The superficial branch of the radial nerve passes superficial to the extensor retinaculum and does not pass through any extensor compartment. It emerges from beneath brachioradialis to enter the dorsum of the wrist and hand.

• Entrapment or irritation can produce Wartenberg’s syndrome
• Symptoms include pain, numbness, and tingling over the dorsoradial hand, especially the dorsum of the thumb and first web space
• It may mimic de Quervain’s tenosynovitis; sensory symptoms and nerve tenderness/Tinel sign help distinguish radial sensory neuritis

Posterior Interosseous Nerve in Compartment IV

The posterior interosseous nerve, the deep branch of the radial nerve after it supplies the extensor compartment muscles, reaches the dorsum of the wrist in relation to the floor of compartment IV. It terminates as a small pseudoganglion and gives articular branches to the wrist and carpal joints.

This is a useful landmark: surgery or pathology in compartment IV should respect the terminal articular branches of the posterior interosseous nerve.

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