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Extensor muscles are those that increase the angle between members of a limb, resulting in backward movement. In the human body, extensor muscles can be found in the hand, foot, back, leg, and arm. Examples of extensors in the hand include the extensor carpi radialis brevis, extensor carpi radialis longus, and extensor carpi ulnaris, which extend the wrist. The extensor digitorum, which extends the fingers, and the extensor indicis, which acts upon the index finger, are also extensors in the hand. Extensors in the foot include the extensor digitorum longus and extensor digitorum brevis, which act upon the toes. The triceps brachii and anconeus are extensors of the forearm, and the elbow is extended by the triceps brachii, anconeus, and brachioradialis.
| Characteristics | Values |
|---|---|
| Definition | Any of the muscles that increase the angle between members of a limb, as by straightening the elbow or knee or bending the wrist or spine backward. |
| Direction of movement | Usually directed backward, with the exception of the knee joint. |
| Body parts | Extensors are found in the hand, foot, elbow, wrist, neck, spine, arm, and fingers. |
| Types of extensors | Extensors can be superficial or deep. |
| Extensors in the hand | Extensor carpi radialis brevis, extensor carpi radialis longus, extensor carpi ulnaris, extensor digitorum, extensor indicis, extensor pollicis brevis, and extensor pollicis longus. |
| Extensors in the foot | Extensor digitorum longus and extensor digitorum brevis. |
| Extensors in the forearm | Triceps brachii, anconeus, supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis. |
| Extensors in the wrist | Extensor digitorum communis (EDC), extensor digiti minimi (EDM), extensor carpi radialis intermedius (ECRI), extensor carpi radialis tertius (ECRT), and extensor carpi radialis accessories (ECRA). |
| Extensors in the fingers | Extensor indicis proprius (EIP) for the index finger, and extensor digiti minimi (EDM) for the small finger. |
| Extensor tendons | Junctura A, B, and C connect the extensor tendons of the fingers. |
| Extensor injuries | Lateral epicondylitis, or "tennis elbow," is a common injury caused by repetitive exertion of the forearm extensor muscles. |
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What You'll Learn
Extensors in the hand
The extensor muscles of the hand are located in the back of the forearm and have long tendons connecting them to bones in the hand, where they exert their action. They extend or open flat the joints in the hand. The extensor expansion of the hand is a specialised connective tissue structure by which the extensor tendons insert onto the phalanges. It is a complex structure that acts to balance forces from a large number of muscles that act on the digits. The extensor expansion is triangular in shape and begins at the level of the metacarpophalangeal joint. It is formed from the extensor digitorum tendon (fingers) and the extensor pollicis longus tendon (thumb).
The extrinsic hand extensors 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 ECRL and ECRB, along with the brachioradialis, form the lateral compartment. The ED divides into four tendons that, along with the EI tendons, pass through the fourth tendon compartment of the dorsal carpal ligament. The EPB inserts into the base of the first phalanx of the thumb to extend and abduct the thumb at the carpometacarpal and MCP joints. The EPL inserts on the base of the distal phalanx of the thumb and uses the dorsal tubercle on the radius as a fulcrum to help the EPB with its action, as well as extending the distal phalanx of the thumb.
The extensor expansion of the hand also includes other muscles that insert onto it, such as the extensor indicis, which is an additional extensor of the index finger, and the extensor digiti minimi, which is an additional extensor of the little finger. The oblique retinacular ligament originates from the proximal phalanx and flexor tendon sheath and inserts onto the lateral bands of the extensor apparatus. It links the motion of the proximal interphalangeal joint (PIPJ) with that of the distal interphalangeal joint (DIPJ). The central slip is the component of the extensor expansion that inserts onto the base of the middle phalanx.
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Extensors in the foot
Extensors are muscles that increase the angle between members of a limb, such as by straightening the elbow or knee or bending the wrist or spine backward. Extensors in the foot include the extensor digitorum longus and extensor digitorum brevis, which originate in the upper and lower parts of the lower leg and act on the toes through long tendons. The extensor hallucis longus and brevis muscles are also extensors in the foot, and they are targeted by exercises such as big toe lifts and big toe extensions with heel raises. Extensor tendons in the foot connect muscles to bones, allowing for the movement of the toes and flexion of the feet.
Extensor tendinopathy or tendonitis can occur when the tendons that run along the top of the foot become irritated and inflamed due to repetitive stress and microtrauma. This can cause pain, especially during activities that involve repetitive motions, and there may also be visible swelling or a bump on the affected tendon. Treatment for extensor tendinopathy or tendonitis typically involves rest, ice, compression, and elevation, as well as avoiding activities that overuse the tendons. Exercises such as towel curls and resistance band big toe abduction can also help improve toe strength and mobility.
The tibialis anterior is the main muscle that lifts the ankle and helps with turning the ankle. It is active during walking when the foot is swinging to lift the ankle and toes and control the foot as it lands. Extensor tendon zones are used by doctors to identify the specific area of irritation or pain, and there are four zones in each foot.
Certain factors can increase the risk of developing extensor tendonitis, including having flat feet or high arches, wearing poorly fitting or tight footwear, and participating in activities that require tight lacing, such as running, dancing, skiing, or ice skating. Additionally, spending long periods standing, walking, or running, especially with a sudden increase in intensity, can contribute to the development of extensor tendonitis.
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Extensors in the forearm
Extensors are muscles that produce movement by lifting a bone or another part of the body. Forearm extensors are muscles that produce extension at the wrist and fingers. The forearm extensors are commonly known as the extensor muscles. They are all innervated by the radial nerve. The muscles in this compartment are organised into two layers: deep and superficial. These two layers are separated by a layer of fascia.
The deep posterior forearm muscles are a group of five muscles located in the deep layer of the posterior compartment of the forearm. These muscles include the supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis. All of the muscles from this group are innervated by the posterior interosseous nerve (C7, C8), a branch of the radial nerve. The blood supply for the deep posterior forearm muscles mainly comes from the anterior and posterior interosseous arteries, the terminal branches of the common interosseous artery. The deep posterior forearm muscles act together to produce movements of the hand and fingers. The prime functions of these muscles are to extend the hand at the wrist joint, extend the first and second digits at the metacarpophalangeal (MCP) and interphalangeal (IP) joints, and abduct the thumb. The only exception is the supinator muscle, which acts specifically on the proximal radioulnar joint to produce supination of the forearm.
The extensor pollicis longus is a slender muscle that extends across the distal half of the forearm. It arises from the posterior surface of the middle third of the ulna and the interosseous membrane and runs distally and medially across the distal radioulnar joint. Just proximal to the wrist, the extensor pollicis longus extends into a tendon that inserts onto the base of the distal phalanx of the thumb. Like other muscles from this group, the extensor pollicis longus receives its nervous supply via the posterior interosseous nerve (C7,C8). Its blood supply comes from the posterior and anterior interosseous arteries. The prime function of the extensor pollicis longus is to extend the thumb in the metacarpophalangeal and interphalangeal joints.
The extensor pollicis brevis is a short, posterior forearm muscle that originates from the distal third of the radius and the adjacent interosseous membrane and inserts onto the base of the proximal phalanx of the thumb. The extensor pollicis brevis muscle is innervated by the posterior interosseous nerve (C7, C8). Its blood supply is provided via the posterior and anterior interosseous arteries. This muscle primarily acts as an extensor of the thumb at the carpometacarpal and metacarpophalangeal joints. This action occurs together with the action of its long counterpart, the extensor pollicis longus muscle.
The supinator muscle has superficial and deep heads that help to supinate the forearm. Passing between these two heads is the deep branch of the radial nerve. The extensor carpi ulnaris is located on the medial aspect of the posterior forearm. Due to its position, it is able to produce adduction as well as extension at the wrist. The extensor digitorum is the main extensor of the fingers. The extensor digitorum runs under the extensor retinaculum and divides to attach to the extensor hoods of the middle and distal phalanx of each of the digits two through five.
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Extensors in the elbow
The elbow is a complex joint that provides mobility and stability to the hand and forearm. Extensor muscles are those that increase the angle between the members of a limb, such as straightening the elbow or bending the wrist backward.
The primary extensor muscle of the elbow is the triceps brachii, a long muscle that runs from the scapula to the olecranon of the ulna. It is assisted by the anconeus, a much smaller muscle that originates at the distal end of the humerus near the elbow and also attaches to the olecranon. These two muscles work together to straighten the arm, with the olecranon locking into the olecranon fossa of the humerus at full extension.
The triceps brachii is considered the major elbow extensor, while the elbow flexors include the biceps brachii, brachialis, and brachioradialis. The biceps brachii is particularly interesting as it contributes significantly to the stability of the shoulder joint and can also supinate the forearm, turning the palm of the hand anteriorly. The brachialis is the primary flexor of the elbow, and the brachioradialis is the third flexor muscle.
The forearm can be divided into two compartments by deep fascia: the anterior compartment containing the flexor muscles and the posterior compartment housing the extensor muscles. The posterior compartment can be further subdivided into superficial and deep extensors. Superficial extensors consist of seven muscles, including the brachioradialis and extensor carpi radialis longus, while deep extensors include five muscles such as the supinator and abductor pollicis longus.
The elbow is a common site for injuries due to the many muscles originating or inserting near it. Tennis elbow, or lateral epicondylitis, is a condition where the forearm muscles and tendons degenerate or suffer microtears due to overuse. It commonly affects athletes and individuals with jobs requiring vigorous forearm use, such as painters, plumbers, and carpenters. Treatment typically involves a multidisciplinary team, including doctors, physical therapists, and sometimes surgeons.
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Extensors in the wrist
Extensor muscles are those that increase the angle between members of a limb, like straightening the elbow or bending the wrist backward. The wrist extensors are a significant component of the posterior forearm musculature. They generally originate on or near the lateral epicondyle and insert on the distal forearm or in the hand.
The extensor tendon compartments of the wrist are six tunnels that transmit long extensor tendons from the forearm into the hand. They are located on the posterior aspect of the wrist. Each tunnel is lined internally by a synovial sheath and separated from one another by fibrous septa. The six extensor compartments of the wrist serve as tunnels for tendons to pass from the forearm to the wrist. At the wrist, the extensor retinaculum of the hand overlies the tendons of the extensor compartment of the wrist. It provides support as well as prevents bowstringing of the tendons.
The first extensor compartment is located on the lateral (radial) aspect of the wrist and transmits two tendons: the abductor pollicis longus (APL) and extensor pollicis brevis (EPB). These tendons form the lateral and medial borders of the anatomical snuffbox, respectively. The second extensor compartment contains the tendons of the extensor carpi radialis longus (ECRL) and extensor carpi radialis brevis (ECRB). The third extensor compartment conducts the extensor pollicis longus (EPL) tendon, which forms the medial border of the anatomical snuffbox. The fourth extensor compartment transmits the tendons of the extensor digitorum and extensor indicis. The fifth extensor compartment contains the extensor digiti minimi tendon, which travels into the little finger. The sixth compartment is located on the medial (ulnar) aspect of the wrist and conducts the tendon of the extensor carpi ulnaris (ECU).
The ECU inserts at the base of the 5th metacarpal to extend and adduct the wrist. The APL inserts into the radial side of the base of the first metacarpal bone to abduct the thumb at the carpometacarpal joint and may continue to abduct the wrist. The EPB inserts into the base of the first phalanx of the thumb to extend and abduct the thumb at the carpometacarpal and MCP joints. The EPL inserts on the base of the distal phalanx of the thumb and uses the dorsal tubercle on the radius as a fulcrum to help the EPB with its action, as well as extending the distal phalanx of the thumb.
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Frequently asked questions
Extensor muscles are muscles that increase the angle between members of a limb, such as straightening the elbow or knee, or bending the wrist or spine backward.
Extensor muscles in the arm include the extensor carpi radialis longus, extensor carpi radialis brevis, and extensor digitorum.
Extensor muscles in the hand include the extensor digitorum, extensor indicis, extensor pollicis brevis, and extensor pollicis longus.
Extensor muscles in the foot include the extensor digitorum longus and extensor digitorum brevis.
Lateral epicondylitis, commonly known as "tennis elbow", is an injury to the forearm extensor muscles attached to the lateral epicondyle of the humerus.
