Dominic Stone
Extensor muscles are those that increase the angle between members of a limb, resulting in backward movement. This includes straightening the elbow or knee, or bending the wrist or spine backward. Extensor muscles in the hand include the extensor carpi radialis brevis, extensor carpi radialis longus, and extensor carpi ulnaris, which extend the wrist, and the extensor digitorum, which extends the fingers. In the foot, extensors include the extensor digitorum longus and extensor digitorum brevis, which act on the toes. The elbow contains seven major muscles that extend it, including the triceps brachii and anconeus, and nine muscles that cross the elbow to act on the wrist and hand.
| 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 backward, except in the case of the knee joint |
| Extensor Muscles in the Hand | Extensor carpi radialis brevis, extensor carpi radialis longus, extensor carpi ulnaris, extensor digitorum, extensor indicis, extensor pollicis brevis, extensor pollicis longus |
| Extensor Muscles in the Foot | Extensor digitorum longus, extensor digitorum brevis |
| Extensor Muscles in the Forearm | Supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, extensor indicis, anconeus |
| Extensor Muscles in the Elbow | Triceps brachii, anconeus |
| Extensor Muscles in the Wrist | Extensor carpi radialis muscles, extensor digitorum communis (EDC), extensor digiti minimi (EDM), extensor carpi ulnaris |
| Extensor Muscle Injury | Lateral epicondylitis, also known as "tennis elbow," is a common injury caused by repeated use of the superficial 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 that connect them to bones in the hand, where they exert their action. The extensor expansion of the hand is a specialised connective tissue structure by which the extensor tendons insert onto the phalanges.
The extensor expansion is triangular in shape and begins at the metacarpophalangeal joint. It is formed from the extensor digitorum tendon (fingers) and the extensor pollicis longus tendon (thumb). As the long extensor tendons approach the metacarpophalangeal joint, they begin to flatten and form the extensor hood. Fibres from the extensor hood fan out and wrap around the distal metacarpal and proximal phalanx.
The extensor muscles of the hand include the extensor pollicis longus, extensor pollicis brevis, extensor carpi radialis longus, extensor carpi radialis brevis, extensor carpi ulnaris, extensor digitorum, and extensor digiti minimi. The extensor carpi radialis longus has the most proximal origin of the extrinsic hand extensors. It originates just distal to the brachioradialis at the lateral supracondylar ridge of the humerus, the lateral intermuscular septum, and by a few fibres at the lateral epicondyle of the humerus.
The extensor digitorum divides into four tendons which, with the extensor indicis tendons, go through the fourth tendon compartment of the dorsal carpal ligament. On the back of the hand, the extensor digitorum tendons diverge to follow the fingers, and the extensor indicis tendon joins the ulnar side of one of the extensor digitorum tendons along the back of the index finger. The extensor digiti minimi takes a similar course as the extensor indicis, except it follows the extensor digitorum tendon along the little finger.
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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 brevis and extensor hallucis longus muscles are also present in the foot and are targeted by exercises such as the big toe lift and big toe extension with heel raises.
Extensor tendinopathy is a condition that involves the tendons that run along the top of the foot, attaching to muscles that lift the foot and help clear the ground when walking. Extensor tendonitis is a specific type of tendonitis that affects the extensor tendons in the foot, causing pain and difficulty in moving the foot. It is often caused by repetitive use or overuse of the tendons, particularly in those with flat feet or high arches. Treatment for extensor tendonitis includes rest, ice, elevation, and avoiding activities that overuse the tendons.
The extensor hallucis longus muscle passes deep to the extensor retinaculum before inserting at the base of the distal phalanx of the big toe. It is responsible for extending the metatarsophalangeal and interphalangeal joints of the big toe, as well as assisting in the inversion of the foot and dorsiflexion of the ankle. Weakness in the extensor hallucis longus can lead to decreased extension at these joints.
The extensor digitorum longus and extensor digitorum brevis muscles act on the toes through long tendons. They originate in the upper and lower parts of the lower leg and are involved in the extension and movement of the toes. These muscles are important for maintaining balance and stability during various activities such as walking, running, or jumping.
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Extensors in the elbow
Extensors 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. In the elbow, the extensor muscles can be divided into two groups: superficial extensors and deep extensors.
The superficial extensors consist of seven muscles: the brachioradialis, extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, and the anconeus. The anconeus and triceps brachii act as the extensors of the forearm. The triceps brachii is a long muscle that runs from the scapula to the olecranon of the ulna. The anconeus is a much smaller muscle that begins at the distal end of the humerus near the elbow and ends at the olecranon. Working together, these muscles increase the angle between the humerus and the ulna and radius, straightening the arm until the olecranon locks into the olecranon fossa of the humerus at full extension.
The deep extensors include five muscles: the supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis. The supinator is one of two muscles that cross the elbow to accomplish the rotation of the forearm. The other muscle is the pronator teres, which is considered a secondary elbow flexor.
The elbow is a common site for injuries such as lateral epicondylitis, also known as "tennis elbow". Tennis elbow is caused by the degeneration or microtearing of the tendons that join the forearm muscles on the outside of the elbow due to overuse. It is common in athletes and people with jobs that require vigorous use of the forearm muscles, such as painters, plumbers, and carpenters. Treatment for tennis elbow usually involves a team approach, including primary care doctors, physical or occupational therapists, and sometimes surgeons.
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Extensors in the wrist
The wrist extensor muscles 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 carpi radialis brevis (ECRB), extensor carpi radialis longus (ECRL), and extensor carpi ulnaris (ECU) muscles work together to achieve neutral wrist extension movements. The ECU, in particular, inserts at the base of the 5th metacarpal to extend and adduct the wrist. It is supplied by the ulnar artery.
The wrist extensors consist of six extensor compartments that serve as tunnels for tendons to pass from the forearm to the wrist. These compartments are lined by a synovial sheath and separated by fibrous septa. The first compartment contains the abductor pollicis longus (APL) and extensor pollicis brevis (EPB) tendons, which are involved in thumb extension and abduction. The second compartment houses the ECRB and ECRL tendons, while the third compartment contains the extensor pollicis longus (EPL) tendon, which acts on the thumb.
The fourth extensor compartment transmits the tendons of the extensor digitorum and extensor indicis, allowing for independent index finger extension. The fifth compartment contains the extensor digiti minimi tendon, which controls the small finger, and the sixth compartment is located on the medial (ulnar) aspect of the wrist, conducting the ECU tendon. These compartments can be affected by De Quervain's tenosynovitis, an inflammation resulting in wrist pain and swelling.
The posterior interosseous nerve (PIN) innervates several muscles in the wrist extensors, including the extensor digitorum communis (EDC), extensor digiti minimi (EDM), and ECU in the superficial wrist extensor compartment. It also innervates the APL, EPB, EPL, and
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Extensors in the forearm
The muscles in the posterior compartment of the forearm are commonly referred to as the extensor muscles. They are responsible for producing extension at the wrist and fingers. 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 these muscles are innervated by the posterior interosseous nerve (C7, C8), a branch of the radial nerve. The blood supply for these muscles mainly comes from the anterior and posterior interosseous arteries, the terminal branches of the common interosseous artery.
The prime functions of the deep posterior forearm 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 specifically acts on the proximal radioulnar joint to produce supination of the forearm.
The extensor pollicis brevis is a short, posterior forearm muscle that originates from the distal third of the radius and the adjacent interosseous membrane. It inserts onto the base of the proximal phalanx of the thumb. This muscle primarily acts as an extensor of the thumb at the carpometacarpal and metacarpophalangeal joints, working in conjunction with its long counterpart, the extensor pollicis longus.
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, running 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. Its primary function is to extend the thumb in the metacarpophalangeal and interphalangeal joints.
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Frequently asked questions
Extensor muscles are muscles that increase the angle between members of a limb, resulting in backward movement. Extension usually results in the straightening of the bones or body surfaces involved.
Extensor muscles can be found in the hand, wrist, forearm, elbow, foot, and knee. Examples of extensor muscles include the extensor carpi radialis brevis, extensor carpi radialis longus, extensor digitorum, extensor indicis, and extensor digitorum longus.
Extensor muscles are responsible for movements such as straightening the elbow, bending the wrist or spine backward, and extending the fingers or toes. They also contribute to abduction and adduction movements at the wrist.
