extensor digitorum muscle (forearm, anatomy)

Last reviewed 01/2018

Extensor digitorum is one of the superficial layer of muscles on the extensor surface of the forearm. It arises from the common extensor origin on the anterior aspect of the lateral epicondyle of the humerus. Passing distally, it occupies most of the posterior aspect of the forearm.

It divides into four tendon slips proximal to the wrist. These pass under the extensor retinaculum within a common synovial sheath. The tendons insert into the extensor expansions of the fingers: the middle slip of each tendon supplies the base of the middle phalange; the two outer slips of each tendon pass to bases of the distal phalanges. Tendons to the ring and little fingers often fuse. The contribution to the little finger extensor hood may only be a small slip.

Extensor digitorum extends the:

  • wrist
  • fingers at the metacarpophalangeal and interphalangeal joints

It is supplied by the posterior interosseous nerve, a branch of the radial nerve (C7,C8).