Extensor compartments of the wrist

The Extensor compartments of the wrist contain the extensor tendons of the hand. It is subdivided into six compartments.

The Posterior Interosseous Nerve is the only nerve found in the dorsal wrist compartments. It is consistently found on the base of the fourth compartment.

The Wrist Extensor Compartments, from lateral to medial, contain the tendons of:

1. abductor pollicis longus (APL) and extensor pollicis brevis (EPB) .
2. extensor carpi radialis longus (ECRL) and brevis (ECRB).
3. extensor pollicis longus (EPL) .
4. extensor digitorum (ED) (four tendons) and extensor indicis (EI) .
5. extensor digiti minimi (EDM) 6. ECU.

As these tendons pass through the compartments, they are invested with synovial sheaths.

The mnemonic 2 2 1 2 1 1 can be used to remember the number of tendons in each compartment.

See Also: Wrist Anatomy

Extensor compartments of the wrist

Compartment	Tendons	Associated Conditions
1	– Abductor Pollicus Longus (EPL) – Extensor Pollicus Brevis (APL)	De Quervain’s tenosynovitis
2	– Extensor Carpi Radialis Brevis (ECRB) – Extensor carpi Radialis longus (ECRL)	Intersection syndrome
3	– Extensor Pollicis Longus (EPL)	Late rupture after closed treatment of distal radius fracture
4	– Extensor Digitorum Communis (EDC) – Extensor Indicis Proprius (EIP)	Extensor tenosynovitis
5	– Extensor Digiti Minimi	Vaughn-Jackson syndrome (initial)
6	– Extensor Carpi Ulnaris (ECU)	ECU instability

See Also: De Quervain's tenosynovitis

The posterior (dorsal) wrist extensor compartments serve to enhance the efficiency and effectiveness of the wrist and finger extensors. Proximal to the metacarpal heads, juncturae tendineae connect the four tendons of the ED muscles, limiting their independent motion. For example, flexion of the middle and little fingers restricts extension of the ring finger MCP joint because the juncturae tendineae pulls the ring finger extensor tendon distally. Conversely, extension of the ring finger exerts an extensor force upon its neighbors, such that they can be actively extended even if the middle and little finger extensor tendons are severed proximal to the juncturae.

The Extensor Retinaculum

At the point where the tendons cross the wrist, there is a ligamentous structure called a retinaculum that appears to lay over the tendons and their sheaths. This retinaculum serves to prevent the tendons from “bowstringing” when the tendons turn a corner at the wrist.

The extensor retinaculum extends from the lateral border of the distal radius across the posterior (dorsal) surface of the distal forearm onto the posterior surface of the distal ulna and ulnar styloid process. It then wraps part way around the ulna to attach to the triquetrum and pisiform bones. The retinaculum and the underlying bones form six tunnel-like structures called fibroosseous compartmentson the dorsum of the wrist.

References

1. Ramage JL, Varacallo M. Anatomy, Shoulder and Upper Limb, Wrist Extensor Muscles. [Updated 2021 Aug 30]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK534805/
2. Moore JS: De Quervain , s tenosynovitis: Stenosing tenosynovits of the first posterior (dorsal) compartment. J Occup Environ Med 39:990–1002, 1997.
3. Wadsworth CT: Anatomy of the Hand and Wrist, Manual Examination and Treatment of the Spine and Extremities. Baltimore, MD: Williams & Wilkins Co, 1988:128–138.
4. Waggy C: Disorders of the wrist. In: Wadsworth C, ed. Orthopaedic Physical Therapy Home Study Course – The Elbow, Forearm, and Wrist. La Crosse, WI: Orthopaedic Section, APTA, Inc., 1997.
5. Dutton’s Orthopaedic Examination, Evaluation, And Intervention 3rd Edition.