Extensor Digitorum Muscle: Location and Actions

The extensor digitorum [pronounced ex-TEN-sur dih-ji-TAW-rum] muscle gets its name from the Greek and Latin ex which means “out of”, and the Latin tendere, which means “to stretch”. So an extensor is a muscle that stretches out or straightens out a joint. The word digitorum is from Latin, indicating the digits or fingers. Communis is Latin for “common” and it refers to a muscle which has several branches or structures. 1Doyle, James R., and Michael J. Botte. Surgical Anatomy of the Hand and Upper Extremity. Philadelphia: Lippincott Williams & Wilkins, 2003.

See Extensor Digitorum Trigger Points

The extensor digitorum muscle, also called the extensor digitorum communis, is an extrinsic hand muscle. Located in the posterior forearm, it is thicker at its proximal end and flattens out as it reaches the wrist. It may be the most apparent of all the forearm hand muscles as it is responsible for most of the shape of the dorsal (extensor) surface of the forearm and you can clearly see its tendons when you extend all four fingers. This may tell you its function, which is, in fact to extend the fingers, and it is the only muscle capable of extending all four.

Manual of Structural Kinesiology

Along with several other muscles, it is part of the “extensor compartment” of the forearm. These other muscles are the extensor indicis, extensor digiti minimi, exensor pollicis longus, and extensor pollicis brevis. It also extends the wrist and is sometimes reported to weakly flex the elbow. 2Floyd, R. T., and Clem W. Thompson. Manual of Structural Kinesiology. Dubuque, IA: WCB/McGraw-Hill, 1998. 82.,3Morrey, Bernard F., and Joaquin Sanchez-Sotelo. The Elbow and Its Disorders. Philadelphia, PA: Saunders/Elsevier, 2009.

extensore digitorum muscle illustration
The Extensor Digitorum

Beginning at the distal humerus, the extensor digitorum runs down the dorsal surface of the forearm between the extensor carpi radialis brevis and the extensor carpi ulnaris muscles, which all arise from a common tendon. The muscle then gives way to four tendons on the four fingers. These tendons are united by a oblique bands over the back of the hand so that individual movement of the fingers by the muscle is limited, but not eliminated. The individual parts of the muscle are capable of producing independent finger extension, with the middle and ring extensors being the most symptomatic for trigger points. The tendons on the index and little fingers are commonly joined by thicker tendons from the extensor indicis and the digiti minimi muscles.

The action of the extensor digitorum in finger extension is significant and the muscle can be overworked by frequent forceful gripping or repetitive actions of the fingers. Strength trainees engaging in dedicated grip strength training, especially high volume repetitive training, can certainly overload this muscle as any powerful flexion of the fingers requires great activity of the antagonistic extensors, especially since, without them, strong flexion of the fingers while closing the grip would also cause the wrist to bend (flex). Trigger points in the extensor digitorum can cause pain in the forearm, hand, and fingers. 4Simons, David G., Janet G. Travell, Lois S. Simons, and Janet G. Travell. “Chp. 8: Masseter Muscle.” Travell & Simons’ Myofascial Pain and Dysfunction: the Trigger Point Manual. Baltimore: Williams & Wilkins, 1999. 329.

The Elbow and Its Disorders (ELBOW & ITS DISORDERS (MORREY))

Extensor Digitorum Origin, Insertion, and Action

Origin: The common extensor origin which is a smooth area on the anterior distal aspect of the lateral epicondyle of the humerus. Its tendon is fused together with the tendons of the extensor carpi radialis brevis, the extensor digiti minimi, and the extensor carpi ulnaris. There are also attachments arising from the adjacent intermuscular septa and from the fascia of the forearm muscles which neighbor. 5Floyd, R. T., and Clem W. Thompson. Manual of Structural Kinesiology. Dubuque, IA: WCB/McGraw-Hill, 1998. 82.,6MacAuley, Domhnall, and Thomas M. Best. “Chp. 21.” Evidence-based Sports Medicine. Malden, MA: BMJ /Blackwell Pub., 2007. 420.

The Extensor Tendons

Insertion: Four separate tendons form a myotendinous junction around one-third of the way up the distal forearm (2/3 of the way down the proximal forearm). Initially somewhat attached, the tendons separate at the extensor retinaculum and form complex attachments at base of the distal phalanx and middle phalanx of each finger, with attachments on the proximal phalanges also being possible (The tendons and the extensor mechanism they are a part of have many possible variations and are highly complex).

Locating the Extensor Digitorum
Locating the Extensor Digitorum

Actions: Extension of the four fingers, primarily at the metacarpophalangeal joints. Also some extension of the proximal interphalangeal joints, assisting the interossei and lumbricals. Some separation (adduction) of the fingers. Wrist extension. 7Floyd, R. T., and Clem W. Thompson. Manual of Structural Kinesiology. Dubuque, IA: WCB/McGraw-Hill, 1998. 82.,8Doyle, James R., and Michael J. Botte. Surgical Anatomy of the Hand and Upper Extremity. Philadelphia: Lippincott Williams & Wilkins, 2003.

See Extensor Digitorum Trigger Points and Referred Pain Patterns

Sources   [ + ]

1. Doyle, James R., and Michael J. Botte. Surgical Anatomy of the Hand and Upper Extremity. Philadelphia: Lippincott Williams & Wilkins, 2003.
2, 5, 7. Floyd, R. T., and Clem W. Thompson. Manual of Structural Kinesiology. Dubuque, IA: WCB/McGraw-Hill, 1998. 82.
3. Morrey, Bernard F., and Joaquin Sanchez-Sotelo. The Elbow and Its Disorders. Philadelphia, PA: Saunders/Elsevier, 2009.
4. Simons, David G., Janet G. Travell, Lois S. Simons, and Janet G. Travell. “Chp. 8: Masseter Muscle.” Travell & Simons’ Myofascial Pain and Dysfunction: the Trigger Point Manual. Baltimore: Williams & Wilkins, 1999. 329.
6. MacAuley, Domhnall, and Thomas M. Best. “Chp. 21.” Evidence-based Sports Medicine. Malden, MA: BMJ /Blackwell Pub., 2007. 420.
8. Doyle, James R., and Michael J. Botte. Surgical Anatomy of the Hand and Upper Extremity. Philadelphia: Lippincott Williams & Wilkins, 2003.