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Extensor muscles are muscles that increase the angle between members of a limb, resulting in backward movements such as straightening the elbow or knee or bending the wrist or spine backward. They are commonly found in the posterior forearm, where they produce extension at the wrist and fingers. Extensor muscles are also found in the hand and foot, such as 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.
| Characteristics | Values |
|---|---|
| Location | Posterior forearm |
| Function | Produce extension at the wrist and fingers |
| Innervation | Radial nerve |
| Layers | Two (superficial and deep) |
| Superficial layer muscles | Extensor carpi radialis brevis, extensor digitorum, extensor carpi ulnaris, extensor digiti minimi |
| Deep layer muscles | Supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, extensor indicis |
| Extensor mechanism of the hand | Interlink between radial nerve-innervated extrinsic extensor system and ulnar nerve-innervated intrinsic system |
| Extensor mechanism of the finger | Extrinsic muscles (extensor digitorum communis) and intrinsic muscles (lumbrical and dorsal interosseous muscles) |
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What You'll Learn
Extensors in the forearm
Extensors are muscles that produce movement by increasing the angle between two bones or body surfaces at a joint. This usually results in the straightening of the bones or body surfaces involved. For example, extension is produced by extending a flexed (bent) elbow. Straightening the arm requires extension at the elbow joint.
The muscles in the posterior compartment of the forearm are commonly referred to as the extensor muscles. These muscles generally function to produce extension at the wrist and fingers. 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 superficial layer of the posterior forearm contains seven muscles. Four of these muscles (extensor carpi radialis brevis, extensor digitorum, extensor carpi ulnaris, and extensor digiti minimi) share a common tendinous origin at the lateral epicondyle. The extensor carpi radialis muscles are situated on the lateral aspect of the posterior forearm. Due to their position, they are able to produce abduction as well as extension at the wrist. The extensor digiti minimi is thought to originate from the extensor digitorum muscle. In some people, these two muscles are fused together. It lies medially to the extensor digitorum. It originates from the lateral epicondyle of the humerus and attaches, with the extensor digitorum tendon, into the extensor hood of the little finger.
The extensor mechanism of the hand relies on an intricate link between the radial nerve-innervated extrinsic extensor system, which originates in the forearm, and the ulnar nerve-innervated intrinsic system, which originates in the hand. Injury to the extensor tendon mechanism is more common than flexor tendon injury due to the more superficial anatomical location of these tendons.
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Extensors in the hand
The extrinsic extensor muscles of the hand 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 carpi radialis muscles are situated on the lateral aspect of the posterior forearm, allowing them to produce abduction and extension at the wrist.
The extensor digitorum, extensor indicis, and extensor digiti minimi are the extrinsic extensors of the fingers. They originate primarily from the lateral epicondyle of the humerus and the dorsal surfaces of the radius and ulna. The extensor digiti minimi is a small muscle interconnected with the extensor digitorum, and they both share a common tendinous origin at the lateral epicondyle. The extensor digitorum divides into four tendons, which, along with the EI tendons, pass through the dorsal carpal ligament. On the back of the hand, the ED tendons diverge to follow the fingers, while the EI tendon joins the ulnar side of one of the ED tendons along the back of the index finger.
The extensor expansion of the hand is a specialised connective tissue structure that allows the extensor tendons to insert onto the phalanges. It is a complex structure that balances the forces from multiple muscles acting on the digits. The extensor expansion is triangular and begins at the metacarpophalangeal joint, where the long extensor tendons flatten to form the extensor hood. Fibres from the extensor hood wrap around the distal metacarpal and proximal phalanx. The extensor hood receives contributions from the extensor digitorum tendon (fingers) and the extensor pollicis longus tendon (thumb).
The extensor mechanism of the hand relies on the intricate link between the radial nerve-innervated extrinsic extensor system, which originates in the forearm, and the ulnar nerve-innervated intrinsic system, which originates in the hand. The extrinsic extensors of the hand are supplied by the posterior interosseous nerve, a branch of the radial nerve. The extensor tendons are susceptible to injuries, and extensor tendon zones help identify the region of injury in the hand and wrist.
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Extensors in the fingers
Extensors are muscles that produce movement in the joints of the human body. This movement increases the angle between two bones or body surfaces at a joint, usually resulting in the straightening of the bones or body surfaces involved. For example, extension is produced by extending a flexed (bent) elbow. Straightening of the arm would require extension at the elbow joint.
The extrinsic 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. Extensor muscles are also present in the fingers, and they help to extend or open flat the joints in the hand. These muscles originate primarily from the lateral epicondyle of the humerus and from the dorsal surfaces of the radius and ulna. The bellies of these muscles are located close to the bellies of the wrist extensor muscles.
The extrinsic extensors of the fingers include the extensor digitorum, the extensor indicis, and the extensor digiti minimi. The extensor digitorum is the major extrinsic extensor muscle, and its degree of independent control has been analysed in studies. The extensor digiti minimi is a small muscle that is interconnected with the extensor digitorum. Tendons of these muscles cross the wrist in synovial-lined compartments, located within the extensor retinaculum. Distal to the extensor retinaculum, the tendons of the extensor digitorum course to the dorsal side of the fingers (one to each finger). The extensor indicis sends one tendon to the index finger.
The extensor mechanism of the hand is a unique system that relies on an intricate link between the radial nerve-innervated extrinsic extensor system, which originates in the forearm, and the ulnar nerve-innervated intrinsic system, which originates in the hand. Injury to the extensor tendon mechanism is more frequent than flexor tendon injury due to the more superficial anatomical location of these tendons. Lateral epicondylitis (tennis elbow) refers to inflammation of the periosteum of the lateral epicondyle and is caused by repeated use of the superficial extensor muscles, which strain their common tendinous attachment to the lateral epicondyle.
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Extensors in the wrist
Extensors are muscles that produce movement by increasing the angle between two bones or body surfaces at a joint. This movement usually results in the straightening of the bones or body surfaces involved. For example, straightening a bent elbow requires extension at the elbow joint.
The muscles in the posterior compartment of the forearm are commonly referred to as the extensor muscles. These muscles generally function to produce extension at the wrist and fingers. The extensor muscles in the forearm are organised into two layers: a deep layer and a superficial layer. The superficial layer of the posterior forearm contains seven muscles, four of which (extensor carpi radialis brevis, extensor digitorum, extensor carpi ulnaris, and extensor digiti minimi) share a common tendinous origin at the lateral epicondyle. The extensor carpi radialis muscles are situated on the lateral aspect of the posterior forearm, allowing them to produce abduction and extension at the wrist. The extensor digitorum is the main extensor of the fingers.
The extrinsic extensors of the fingers are the extensor digitorum, the extensor indicis, and the extensor digiti minimi. These muscles originate primarily from the lateral epicondyle of the humerus and the dorsal surfaces of the radius and ulna. The extensor digiti minimi is thought to originate from the extensor digitorum muscle, and in some people, these two muscles are fused together. The extensor digiti minimi is a small muscle that contributes to extension at the wrist.
The extensor mechanism of the hand relies on a complex link between the radial nerve-innervated extrinsic extensor system, which originates in the forearm, and the ulnar nerve-innervated intrinsic system, which originates in the hand. 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 provides support for the tendons of the extensor compartment and prevents bowstringing.
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Extensors in the foot
Extensor tendinopathy can be caused by overuse, such as from repeated motions, and can be aggravated by wearing poorly fitting shoes. Symptoms include an aching pain at the top of the foot and front of the ankle. Treatment for extensor tendinopathy usually begins with at-home exercises. It can be treated with over-the-counter medications, such as NSAIDs like aspirin or ibuprofen, which can reduce pain and inflammation.
To treat extensor tendinitis at home, you can follow the RICE method:
- Rest: Avoid the activity that irritated your tendons.
- Ice: Apply a cold compress to your foot for 15 minutes at a time, four times a day.
- Compression: Wrap the painful area in an elastic bandage to help reduce swelling.
- Elevation: Prop your foot above the level of your heart as often as you can.
It is important to note that flat shoes may aggravate symptoms, especially if paired with tight calf muscles. Shoes with flexible soles generally offer less support and can increase stress in the soft tissues of the foot and ankle.
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Frequently asked questions
Extensor muscles are found in the posterior compartment of the forearm.
Some examples of extensor muscles in the forearm include the extensor digitorum, extensor carpi ulnaris, and extensor digiti minimi.
The extensor digitorum muscle is involved in extending the four medial fingers and generating a pull for the extension of the wrist.
The deep muscles in the forearm include the extensor pollicis brevis, abductor pollicis longus, extensor pollicis longus, extensor digitorum communis, and extensor indicis proprius.
Yes, extensor muscles can also be found in the back, leg, hand, and foot. For example, the rectus femoris muscle and extensor digitorum longus are extensors in the leg and foot, respectively.
