Dominic Stone
The extensor pollicis longus muscle (EPL) is a skeletal muscle located on the dorsal side of the forearm. It is responsible for extending the thumb at the carpometacarpal, metacarpophalangeal, and interphalangeal joints. The EPL muscle is much larger than the extensor pollicis brevis muscle, and it arises from the dorsal surface of the ulna and the interosseous membrane. The tendon of the EPL passes through the third extensor compartment of the wrist and is involved in various pathologies, including stenosing tenosynovitis and spontaneous tendon rupture.
| Characteristics | Values |
|---|---|
| Full Form | Extensor Pollicis Longus Muscle |
| Location | Dorsal side of the forearm |
| Type | Skeletal muscle |
| Innervation | Posterior interosseous nerve (C7 and C8) |
| Blood Supply | Anterior interosseous artery, posterior interosseous artery, radial artery, and ulnar artery |
| Attachments | Originates from the posterior surface of the ulna and interosseous membrane |
| Actions | Extension at the interphalangeal, metacarpophalangeal and carpometacarpal joints of the thumb |
| Tendon | Forms the ulnar border of the anatomical snuffbox |
| Function | Extends and adducts the thumb |
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What You'll Learn
Extensor pollicis longus (EPL) muscle location
The extensor pollicis longus muscle (EPL) is a skeletal muscle located in the forearm. It is one of the extrinsic muscles of the hand. It is much larger than the extensor pollicis brevis muscle, the origin of which it partly covers.
The EPL is located within the deep compartment of the posterior forearm. It arises from the dorsal surface of the ulna and from the interosseous membrane, next to the origins of the abductor pollicis longus and extensor pollicis brevis. It passes through the third tendon compartment, lying in a narrow, oblique groove on the back of the lower end of the radius. It then crosses the wrist close to the dorsal midline before turning towards the thumb using Lister's tubercle on the distal end of the radius as a pulley.
The EPL tendon defines the ulnar border of the anatomical snuffbox, which is a triangular interval between the EPL and the extensor pollicis brevis. The radial artery is found within this anatomical snuffbox. The EPL tendon inserts on the dorsum of the distal phalanx of the thumb and is responsible for active extension of the distal phalanx.
The EPL is an important contributor to thumb function. It extends and adducts the thumb metacarpophalangeal (MCP) and interphalangeal (IP) joints. It also serves as an accessory extensor and adductor of the metacarpophalangeal of the proximal phalanx and carpometacarpal joints of the first metacarpal. The integrity of the EPL can be assessed by asking a patient to place their hand flat on a table and then raise their thumb off the table (retropulsion). This movement is solely controlled by the EPL.
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EPL function
The extensor pollicis longus muscle (EPL) is an extrinsic thumb muscle that extends and adducts the thumb metacarpophalangeal (MCP) and interphalangeal (IP) joints. It is a skeletal muscle located dorsally on the forearm, and it is much larger than the extensor pollicis brevis. The EPL arises from the dorsal surface of the ulna and the interosseous membrane, next to the origins of the abductor pollicis longus and extensor pollicis brevis. It passes through the third tendon compartment, lying in a narrow, oblique groove on the back of the lower end of the radius. It then crosses the wrist close to the dorsal midline before turning towards the thumb using Lister's tubercle on the distal end of the radius as a pulley.
The EPL is responsible for active extension of the distal phalanx of the thumb. It is the only muscle that can achieve full hyperextension at the interphalangeal joint. To test whether the EPL tendon is intact, a patient can be asked to place their hand flat on a table and then raise their thumb (retropulsion). This movement is solely controlled by the EPL.
The EPL receives innervation from the posterior interosseous nerve (C7 and C8), which is a continuation of the deep branch of the radial nerve. Before the tendon enters its synovial sheath, arteries from the anterior interosseous artery or its muscular branches enter the tendon. The sheath itself is supplied by the posterior ramus of the same artery. In the metacarpal region, beyond the synovial sheath, the tendon is supplied directly from the radial artery. At the phalanges, the tendon forms a dorsal aponeurosis supplied by a digital branch of the first dorsal metacarpal artery.
The EPL is an important contributor to thumb function, and its integrity can be assessed through simple tests. However, understanding its anatomy is also crucial for understanding potential pathologies, particularly those that may compromise dynamic thumb function.
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EPL tendon
The extensor pollicis longus (EPL) tendon is a vital component of the human forearm, enabling thumb movement and contributing to the intricate mechanics of the hand and wrist. This tendon is integral to the functioning of the extensor pollicis longus muscle, which is responsible for the active extension of the distal phalanx of the thumb.
The EPL tendon originates from the extensor pollicis longus muscle, which arises from the dorsal surface of the ulna and the interosseous membrane. The muscle passes through the third tendon compartment, located on the back of the lower end of the radius bone in the forearm. From there, it crosses the wrist and turns towards the thumb, utilising Lister's tubercle on the distal end of the radius as a pulley.
The EPL tendon plays a crucial role in thumb movement. It inserts on the dorsum of the distal phalanx of the thumb, allowing for its extension. The tendon works in conjunction with the abductor pollicis brevis and adductor pollicis muscles, which are attached to it. Together, they enable the extension of the thumb's interphalangeal joint to a neutral position. However, only the EPL tendon can achieve full hyperextension at this joint.
The EPL tendon receives its blood supply from various arterial branches. Before the tendon enters its synovial sheath, it is supplied by the anterior interosseous artery and its muscular branches. Within the sheath, the posterior ramus of the same artery provides the necessary blood flow. As the tendon moves beyond the sheath and into the metacarpal region, it receives a direct supply from the radial artery. Finally, at the phalanges, a digital branch of the first dorsal metacarpal artery, which originates from the radial artery, supplies the EPL tendon.
Injuries to the EPL tendon can have significant consequences on thumb function. A rupture of the tendon can lead to a flexion deformity of the interphalangeal (IP) joint and an inability to actively extend the distal phalanx. However, in some cases, the extension of the intrinsic thumb muscles and adhesions between the EPL tendon and the extensor pollicis brevis tendon allow for the retention of active extension of the IP joint, even with a ruptured EPL tendon.
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EPL innervation
The extensor pollicis longus muscle (EPL) is a skeletal muscle located dorsally on the forearm. It is responsible for active extension of the distal phalanx of the thumb. The EPL tendon inserts on the dorsum of the distal phalanx of the thumb. The EPL is the only muscle that can extend the thumb at the metacarpophalangeal and interphalangeal joints. It also assists in the supination of the forearm, as well as extension and abduction of the wrist joint.
The EPL muscle receives innervation from the posterior interosseous nerve (C7 and C8), which is a continuation of the deep branch of the radial nerve. The tendon of the EPL receives its blood supply from the anterior interosseous artery, the posterior interosseous artery, the radial artery, and the ulnar artery.
The integrity of the EPL can be assessed by asking the patient to place their hand flat on a table and then raise their thumb off the table. This movement is solely controlled by the EPL muscle. A rupture of the EPL tendon can lead to a flexion deformity of the IP joint and an inability to actively extend the distal phalanx. However, in some patients, the extension of the intrinsic muscles of the thumb and adhesions between the EPL and extensor pollicis brevis tendons allow for complete active extension of the IP joint even with a ruptured EPL tendon.
The EPL is located on the posterior aspect of the forearm, extending from the middle third of the ulna and adjacent interosseous membrane to the distal phalanx of the thumb. It passes through the third extensor compartment of the wrist and continues laterally towards the thumb around Lister's tubercle. The EPL is much larger than the extensor pollicis brevis muscle, the origin of which it partly covers.
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EPL pathologies
The extensor pollicis longus muscle (EPL) is a skeletal muscle located at the back of the forearm. It is responsible for extending the thumb at the carpometacarpal and interphalangeal joints, and partially adducting the first metacarpal. The EPL tendon inserts on the dorsum of the distal phalanx of the thumb and is responsible for its active extension.
Another pathology associated with the EPL muscle is tenosynovitis, an inflammatory irritation of the synovial sheath. This condition is relatively common in the third compartment after repetitive activities such as drum playing. De Quervain's tenosynovitis is a specific type of tenosynovitis that affects the abductor pollicis longus and extensor pollicis brevis tendons in the first extensor compartment. It causes pain around the radial styloid associated with thumb movement.
A severe high or proximal injury to the radial nerve can result in the loss of EPL function, along with the loss of function in several other muscles, including the triceps, brachioradialis, supinator, and extensor carpi ulnaris. This type of injury can cause variable sensory loss on the dorsum of the hand and over the anatomical snuffbox area.
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Frequently asked questions
EPL stands for Extensor Pollicis Longus, which is a muscle in the forearm that is responsible for active extension of the distal phalanx of the thumb.
The EPL muscle is located in the deep compartment of the posterior forearm. It passes through the third extensor compartment of the wrist, then continues laterally towards the thumb.
The EPL muscle is responsible for extending and adducting the thumb metacarpophalangeal (MCP) and interphalangeal (IP) joints. It also serves as an accessory extensor and adductor of the metacarpophalangeal of the proximal phalanx and carpometacarpal joints of the first metacarpal.
To test the integrity of the EPL muscle, ask the patient to place their hand flat on a table and then raise their thumb off the table. This movement is solely controlled by the EPL muscle.
