Victor Forge
The human hand is a complex structure, with several muscles working together to enable its range of motion. Extensor muscles are those that increase the angle between members of a limb, such as straightening the elbow or bending the wrist. The extrinsic extensor muscles of the hand are located in the forearm and have long tendons connecting them to bones in the hand. These muscles include the extensor carpi radialis longus (ECRL), extensor carpi radialis brevis (ECRB), extensor digitorum (ED), and extensor digiti minimi (EDM), among others. These muscles are responsible for extending or opening flat the joints in the hand and fingers, with some acting on specific fingers, such as the index finger or thumb. Understanding the anatomy of these muscles is important, as injuries to the extensor tendons can occur, impacting the hand's functionality.
| Characteristics | Values |
|---|---|
| Location | Back of the forearm |
| Function | Extend or open flat joints in the hand |
| Muscles Involved | Extensor carpi radialis longus (ECRL), extensor carpi radialis brevis (ECRB), extensor digitorum (ED), extensor digiti minimi (EDM), extensor carpi ulnaris (ECU), abductor pollicis longus (APL), extensor pollicis brevis (EPB), extensor pollicis longus (EPL), extensor indicis (EI) |
| Blood Supply | Radial artery, ulnar artery, posterior interosseous artery |
| Nerve Supply | Radial nerve, posterior interosseous nerve |
| Tendon Connections | Tendons connect to middle, ring, and little fingers; index finger tendon connected to EI |
| Injuries | External flexion force during active extension can cause tendon dislocation into the intermetacarpal space |
| Pathology | Lateral epicondylitis affects 1-5% of the general population |
| Extension of Fingers | Extension of index and little fingers is independent due to separate extensors |
| Extension of Joints | MCP, PIP, and DIP joints |
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What You'll Learn
Extensor carpi radialis longus (ECRL)
The ECRL is one of three primary wrist extensors. It is most effective as a wrist extensor when the elbow is extended and when radial deviation is balanced by the primary ulnar deviator- extensor carpi ulnaris. Functionally, the wrist extensors work strongly in the action of gripping, together with extensor carpi ulnaris. By keeping the wrist in extension, flexion of the wrist by flexors digitorum superficialis and profundus is prevented, with the result that these muscles act on the fingers. When the wrist then moves into flexion, the flexor tendons are unable to shorten enough to generate effective movement at the interphalangeal joints, resulting in a state of active insufficiency.
Radial nerve damage leads to paralysis of the wrist extensors. Intersection syndrome is a bursitis that occurs at the site where the abductor pollicis longus and extensor pollicis brevis tendons cross over the extensor carpi radialis tendons proximal to the extensor retinaculum. This may be due to friction at this site of crossing or it may occur from tenosynovitis of the two extensor tendons within their synovial sheath. This leads to tenderness, swelling, and crepitus and can be confused with de Quervain's syndrome.
The best exercises to improve strength in the ECRL are exercises that require you to move your wrist, hands, elbows, and forearms. Some examples include holding your arm out straight and gently pulling back on your fingertips, holding a weight or a can of food in your hand and slowly lifting it toward your chest and lowering it down, and getting down on your hands and knees, slowly bending your arms to lower your chest toward the floor and then pushing up again, being sure to keep your back straight.
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Extensor carpi ulnaris (ECU)
The ECU is supplied by the radial recurrent artery and the posterior interosseous artery, a branch of the ulnar artery. The nerve supplying the ECU is the posterior interosseous nerve (C7 and C8), which is a continuation of the deep branch of the radial nerve. The ECU is the only forearm extensor that occupies its own fibro-osseous tunnel at the wrist level, passing through the sixth extensor compartment of the wrist.
ECU injuries are common in individuals who engage in activities requiring repetitive arm, elbow, and wrist movements, especially when tightly gripping an object. Symptoms of an ECU injury include pain when shaking hands or squeezing/gripping objects, with the pain intensifying when the wrist is moved forcefully. Diagnosis of an ECU injury often requires imaging techniques like CT, MRI, or ultrasound, and treatment depends on the severity of the injury. Conservative treatments include immobilization and stabilization of the affected wrist with a cast, while more severe cases may require invasive procedures like steroid injections or surgery.
The ECU plays a crucial role in achieving neutral wrist extension movements, working synergistically with other muscles like the extensor carpi radialis brevis (ECRB) and extensor carpi radialis longus (ECRL). Understanding the anatomy and function of the ECU is essential for diagnosing and treating injuries related to the wrist and forearm.
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Extensor digitorum (ED)
ED is a long muscle that runs from the lateral epicondyle of the humerus to the medial four phalanges of the hand. It is the most superficial muscle of the posterior forearm, situated medial to the extensor carpi radialis brevis muscle and lateral to the extensor digiti minimi and extensor carpi ulnaris muscles. ED is innervated by the posterior interosseous nerve, a continuation of the deep branch of the radial nerve.
ED is responsible for extending fingers 2-5, or the index, long, ring, and small fingers. It generates the pull for the extension of the four medial fingers in their metacarpophalangeal and both interphalangeal joints. ED also participates in the extension of the wrist.
ED is supplied by the posterior interosseous artery and the radial recurrent artery. It shares a common synovial tendon sheath with other extensor muscles, which helps to reduce friction between the tendon and the surrounding structures. ED can be easily palpated in the lateral aspect of the posterior forearm, especially during the extension of the hand when it is contracted.
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Extensor digiti minimi (EDM)
Extensor digitorum, indicis, and minimi muscles are located in the back of the forearm and have long tendons connecting them to bones in the hand, where they exert their action. The extensor digiti minimi (EDM) is a slender forearm muscle situated on the ulnar side of the extensor digitorum. It is a long, slender skeletal muscle situated in the posterior compartment of the forearm. It lies between the extensor digitorum and extensor carpi ulnaris and is generally connected to the extensor digitorum. The extensor digitorum communis (EDC) muscles extend the second (index finger), third (long finger), fourth (ring finger), and fifth (small finger) digits. Independent small finger extension is accomplished by the extensor digiti minimi (EDM) muscle.
The EDM muscle is also known as the extensor digiti quinti proprius. It is a muscle of the superficial layer of the posterior compartment of the forearm. With other extensor muscles, it arises from a common extensor tendon attached to the lateral epicondyle of the humerus. The EDM represents a medial group of superficial extensor muscles. The EDM passes under the extensor retinaculum near the wrist and passes through the fifth extensor compartment of the wrist. It is one of the extrinsic muscles of the hand.
The extensor digiti minimi is the muscle that extends the little finger. Several anatomical variations of extensor digiti minimi have been clinically observed. In some cases, there is an additional fibrous slip extending from the lateral epicondyle of the humerus (the origin). Occasionally, the tendon of insertion fails to divide properly, or a fibrous slip is extended to the ring finger. Also, fusion with the extensor digitorum muscle is fairly common. Extensor digiti minimi extends through the fifth extensor compartment. Anatomical variations in this compartment may cause tenosynovitis, which can drastically reduce the function of the extensor digiti minimi.
The extensor digitorum, indicis, and minimi muscles are supplied by the posterior interosseous artery, a branch of the ulnar artery.
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Extensor indicis (EI)
The extensor indicis acts as an accessory extensor of the index finger, allowing it to extend independently from other fingers. It extends the index finger at the metacarpophalangeal and interphalangeal joints. As the index finger has its own separate extensor muscle, the extensor indicis, it can be moved more independently than the other fingers. This muscle also assists in extending the wrist and midcarpal joints.
The extensor indicis arises from the distal third of the dorsal part of the ulna, which is a bone in the forearm, and from the interosseous membrane. It extends inferiorly and narrows into a tendon that passes deep to the extensor retinaculum, a structure that holds the tendons in place. Beneath the retinaculum, the tendon is surrounded by a tendinous sheath, which protects the tendon, along with the tendons of the extensor digitorum muscle.
The tendon of the extensor indicis runs through the fourth tendon compartment of the wrist, also known as the fourth dorsal (extensor) compartment, together with the tendon of the extensor digitorum. The fourth tendon compartment is a passageway for tendons to pass through and is located deep to the extensor retinaculum. The extensor indicis tendon then projects into the dorsal aponeurosis of the index finger, which is a thin, sheet-like structure on the back of the finger.
The extensor indicis is innervated by the posterior interosseous nerve (C7 and C8), which is a continuation of the deep branch of the radial nerve (C7 and C8). It receives its blood supply from the posterior interosseous artery, which is a branch of the ulnar artery.
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Frequently asked questions
The extrinsic extensor muscles of the hand are located in the back of the forearm and include the extensor carpi radialis longus (ECRL), extensor carpi radialis brevis (ECRB), extensor digitorum (ED), extensor digiti minimi (EDM), extensor carpi ulnaris (ECU), abductor pollicis longus (APL), extensor pollicis brevis (EPB), extensor pollicis longus (EPL), and extensor indicis (EI).
The extensor digitorum muscle (also known as extensor digitorum communis) is a muscle of the posterior forearm that extends the medial four digits of the hand.
The extension of the index finger, long finger, ring finger, and small finger occurs via the extensor digitorum communis (EDC) muscles. The independent extension of the index finger is carried out by the extensor indicis proprius (EIP) muscle, while the extensor digiti minimi (EDM) muscle accomplishes the independent extension of the small finger.
The thenar muscle group is found at the base of the thumb and is responsible for pulling the thumb away from the index finger, allowing us to grasp objects.
