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The muscles that extend the wrist are known as the wrist extensors or extrinsic extensor muscles of the hand. They are located in the posterior forearm or back of the forearm, and they generally originate on or near the lateral epicondyle. These muscles 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).
| Characteristics | Values |
|---|---|
| Wrist Extensor Muscles | Extensor Carpi Radialis Brevis (ECRB), Extensor Carpi Radialis Longus (ECRL), Extensor Carpi Ulnaris (ECU) |
| Thumb Extension Muscles | Abductor Pollicis Longus (APL), Extensor Pollicis Brevis (EPB), Extensor Pollicis Longus (EPL) |
| Index Finger Extension Muscle | Extensor Indicis Proprius (EIP) |
| Small Finger Extension Muscle | Extensor Digiti Minimi (EDM) |
| Extension of Second, Third, Fourth, and Fifth Digits Muscles | Extensor Digitorum Communis (EDC) |
| Innervation | Radial Nerve (Deep Branch) |
| Superficial Branch of the Radial Nerve (SBRN) | Sensation in the Distal Forearm and Hand |
| Origin of Extensor Carpi Radialis Longus (ECRL) | Lateral Supracondylar Ridge of the Humerus, Lateral Intermuscular Septum, and Lateral Epicondyle of the Humerus |
| Origin of Extensor Carpi Radialis Brevis (ECRB) | Radial Collateral Ligament and Lateral Epicondyle |
| Origin of Extensor Carpi Ulnaris (ECU) | Lateral Epicondyle, Dorsal Border of the Ulna |
| Origin of Abductor Pollicis Longus (APL) | Posterior Proximal Surface of the Ulna and Radius, Lateral Part of the Dorsal Surface of the Ulna |
| Origin of Extensor Pollicis Brevis (EPB) | Posterior Proximal Surface of the Radius |
| Origin of Extensor Pollicis Longus (EPL) | Posterior Proximal Surface of the Radius |
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What You'll Learn
Extensor Carpi Radialis Brevis (ECRB)
The extensor carpi radialis brevis (ECRB) is a muscle in the forearm that acts to extend and abduct the wrist. It is a part of the superficial layer of the posterior compartment of the forearm, also known as the extensor compartment. The ECRB works in tandem with the extensor carpi radialis longus (ECRL) to achieve these movements.
The ECRB originates from the common extensor tendon attached to the lateral epicondyle of the humerus. It also arises from the radial collateral ligament of the elbow joint and the intermuscular septa between it and the adjacent muscles. The fibres of the ECRB end in the middle of the forearm as a flat tendon, which is closely associated with the ECRL tendon.
The ECRB and ECRL muscles run along the length of the forearm and pass through the second compartment of the extensor retinaculum. The ECRB inserts into the dorsal base of the third metacarpal, while the ECRL inserts into the base of the second metacarpal. This anatomical arrangement allows the ECRB and ECRL to work together to extend and abduct the wrist radially.
Variations in the origins of the radial extensor muscles are rare but have been reported. For example, in a case study, a 75-year-old female cadaver was found to have an accessory tendon arising from the ECRL, which inserted into the base of the third metacarpal, typically associated with the ECRB. Additionally, bilateral agenesis of the ECRB was observed in the same cadaver.
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Extensor Carpi Radialis Longus (ECRL)
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. ECRL works in conjunction with the other muscles and tendons in the arm to help move the wrist and hand. It is also active during fist clenching.
The best exercises to improve strength in the ECRL are exercises that require moving the 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, keeping your back straight.
ECRL can be palpated in the upper lateral portion of the posterior forearm. The tendon of ECRL can be felt in the floor of the anatomical snuffbox when these movements (wrist extension and abduction) are performed.
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Extensor Carpi Ulnaris (ECU)
The extensor carpi ulnaris (ECU) is a skeletal muscle located on the ulnar side of the forearm. It is a key contributor to the extension and adduction of the wrist, playing a crucial role in various activities involving these movements. The ECU is the most medial muscle of the posterior forearm. It originates from the lateral epicondyle of the humerus and the posterior border of the ulna, and inserts onto the dorsal base of the fifth metacarpal. The ECU is innervated by the posterior interosseous nerve (PIN), a branch of the deep division of the radial nerve.
The ECU is an important muscle for athletes and individuals who participate in activities requiring forceful and repetitive wrist movements, such as gripping, throwing, or racket sports. However, this also makes it susceptible to injuries. A common injury associated with the ECU is tennis elbow, which occurs due to repetitive stress on the tendon. Symptoms of ECU injuries include pain during handshakes or when squeezing/gripping objects, with the pain intensifying during forceful wrist movements.
The ECU works in conjunction with other muscles to achieve neutral wrist extension. These include the extensor carpi radialis brevis (ECRB) and extensor carpi radialis longus (ECRL). Together, these muscles contribute to a balanced extension of the wrist without deviating the hand in the transverse plane. This is particularly important for activities that require a strong grip or clenched fist, such as a tennis backhand.
The oblique course of the ECU results in a combined extension and adduction (ulnar deviation) of the hand. This means that its contraction leads to a pulling force in a posterolateral direction. The ECU also provides essential medial stability to the wrist and forearm.
The blood supply to the ECU is provided by branches of the radial recurrent and posterior interosseous arteries, which originate from the radial and ulnar arteries, respectively.
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Extensor Pollicis Brevis (EPB)
The extensor pollicis brevis (EPB) is a skeletal muscle found in the forearm. It is part of a group of muscles known as the wrist extensors, which are a significant component of the posterior forearm musculature. These muscles generally originate near the lateral epicondyle and insert into the distal forearm or hand, allowing for wrist extension. The EPB specifically arises from the ulna distal to the abductor pollicis longus, the interosseous membrane, and the dorsal surface of the radius. Its tendon passes through the same groove as the abductor pollicis longus on the lateral side of the lower end of the radius. The EPB is inserted into the base of the first phalanx of the thumb, also known as the proximal phalanx, contributing to thumb extension.
The EPB is closely associated with the abductor pollicis longus (APL) and the extensor pollicis longus (EPL) muscles. Together, the EPB and EPL tendons form the medial and lateral borders of the anatomical snuffbox, a depression on the dorsal aspect of the wrist. The EPB and APL muscles share a similar direction, and their tendons pass through the same groove on the lateral side of the radius. The APL muscle originates from the posterior proximal surface of the ulna and radius, while the EPL originates from the same region distal to the APL. Both the APL and EPL insert into the dorsal surface of the base of the thumb.
The EPB is part of the deep group of the posterior fascial compartment of the forearm. This compartment is organised into two layers: deep and superficial. The deep layer, which includes the EPB, is innervated by the posterior interosseous nerve (PIN), a continuation of the deep branch of the radial nerve. The PIN innervates several other muscles in the superficial wrist extensor compartment, including the extensor digitorum communis (EDC), extensor digiti minimi (EDM), extensor carpi ulnaris (ECU), and extensor indicis proprius (EIP).
The EPB plays a crucial role in thumb extension, working alongside the APL and EPL muscles. Thumb extension is an important movement that allows for various grasping and manipulative actions. The EPB also contributes to thumb abduction at the carpometacarpal joint. This muscle's function and structure highlight its importance in maintaining the mobility and dexterity of the hand and wrist.
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Extensor Digitorum (ED)
ED shares a common tendinous origin with extensor carpi radialis brevis, extensor carpi ulnaris, and extensor digiti minimi. These muscles can be easily palpated in the lateral aspect of the posterior forearm, especially during hand extension when they are contracted. ED is innervated by the radial nerve (C7 and C8).
In some people, the ED and extensor digiti minimi muscles are fused together. The extensor digitorum muscle also participates in the anatomy of the grip as it contributes to the opening of the hand and letting go of objects.
A common injury affecting the ED muscle is tennis elbow, typically caused by overuse of the extensor muscles attaching at the elbow. Symptoms include weakness in the wrist and hand, along with pain on the outside of the elbow. Treatment involves resting the affected muscle with ice and compression. An exercise to improve wrist mobility is to hold your arm in front of you, with your thumb facing up, and then deviate your hand from side to side.
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Frequently asked questions
The muscles that extend the wrist are known as the extensor muscles. These 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 wrist extensors produce extension and adduction at the wrist and fingers. They are also involved in abduction of the thumb at the carpometacarpal joint.
The wrist extensors are innervated by the radial nerve, specifically the posterior interosseous branch.
