Extensor Pollicis Longus Muscle Anatomy

The extensor pollicis longus (EPL) is larger and its tendon is longer than that of the extensor pollicis brevis. It’s located in the posterior compartment of the forearm. Its tendon is located in the third extensor compartment.

The tendon passes under the extensor retinaculum in its own tunnel, within the tendinous sheath of the extensor pollicis longus, medial to the dorsal tubercle of the radius. It uses the tubercle as a trochlea (pulley) to change its line of pull as it proceeds to the base of the distal phalanx of the thumb. The gap created between the long extensor tendons of the thumb is the anatomical snuff box. In addition to its main actions, the extensor pollicis longus also adducts the extended thumb and rotates it laterally.

Extensor Pollicis Longus Muscle Anatomy

The extensor pollicis longus originates on the middle third of the posterior ulnar diaphysis, traverses laterally along the forearm, passes over Lister’s tubercle, goes through the third osteofibrous tunnel and travels superiorly to the extensor carpi radialis longus, and extensor carpi radialis brevis then inserts on the base of the distal phalanx of the pollex.

See Also: Forearm Muscles Anatomy & Function

The extensor pollicis longus gets innervated by the posterior interosseous nerve that originates from the radial nerve.

It gets its blood supply is from the posterior interosseous artery and perforating branches of the anterior interosseous artery.

The extensor pollicis longus mainly extends the interphalangeal joint of the distal phalanx of the thumb. It also serves as accessory extensors and adductors of the metacarpophalangeal of the proximal phalanx and carpometacarpal joints of the first metacarpal. It may also assist in wrist joint extension.

The tendons of the abductor pollicis longus and extensor pollicis brevis bound the anatomical snuff box anteriorly, and the tendon of the extensor pollicis longus bounds it posteriorly. The snuff box is visible when the thumb is fully extended; this draws the tendons up and produces a triangular hollow between them. Observe that the radial artery lies in the floor of the snuff box. Radial styloid process can be palpated proximally and the base of the 1st metacarpal can be palpated distally in the snuff box. scaphoid and trapezium can be felt in the floor of the snuff box between the radial styloid process and the 1st metacarpal.

Variations in the extensor pollicis longus are rare, with a prevalence of about 1%. These variations can include additional muscle bellies or tendons and atypical pathways, as classified by the Turker Classification. Such anomalies are usually asymptomatic but can be discovered incidentally during surgical procedures for other conditions.

Clinically

The extensor pollicis longus is prone to several pathologies, often related to trauma or medical conditions like rheumatoid arthritis. Common issues include stenosing tenosynovitis and spontaneous tendon rupture. For instance, non-displaced distal radius fractures can lead to EPL rupture in up to 5% of cases, due to the tendon’s proximity to the fracture site and subsequent ischemia or mechanical irritation.

Common Pathologies:

• Stenosing Tenosynovitis: Inflammation leading to tendon sheath constriction
• Tendon Rupture: Often post-trauma, especially distal radius fractures

To test the extensor pollicis longus, the thumb is extended against resistance at the interphalangeal joint. If the extensor pollicis longus is acting normally, the tendon of the muscle can be seen and palpated on the medial side of the anatomical snuff box.

References & More

1. Cael, C. (2010). Functional anatomy: Musculoskeletal anatomy, kinesiology, and palpation for manual therapists. Philadelphia, PA: Wolters Kluwer Health/Lippincott, Williams & Wilkins.
2. Moore, K. L., Dalley, A. F., & Agur, A. M. R. (2014). Clinically Oriented Anatomy (7th ed.). Philadelphia, PA: Lippincott Williams & Wilkins.
3. Clinically Oriented Anatomy – 8th Edition
4. Khan IA, Varacallo M. Anatomy, Shoulder and Upper Limb, Hand Extensor Pollicis Longus Muscle. [Updated 2022 Dec 21]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: Pubmed