Author: Dr Peter de Souza
Last modified: 3 March 2021

The extensor digitorum is one of the muscles of the superficial layer of the posterior compartment of the forearm. It is the main extensor of the four fingers - the index, middle, ring and little fingers.

The posterior compartment of the forearm consists of a superficial layer (7 muscles) and a deep layer (5 muscles).

The muscles in the superficial layer include:

The muscles of the superficial layer share a common origin from the lateral epicondyle and lateral supracondylar ridge of the humerus.

All the muscles of the posterior compartment are innervated by the radial nerve.


  • Lateral epicondyle of the humerus
  • Intermuscular septa of adjacent muscles


  • Extensor hoods/expansions on the dorsal bases of the distal phalanges of the index, middle, ring and littler fingers.

The tendons of the extensor digitorum insert via a triangular connective tissue aponeurosis on the dorsal surfaces of the middle and distal phalanges. The apex of th triangle attaches to the distal phalanx, the central parts attaches to the middle phalanx and the corners of the triangle are wrapped around the sides of the metacarpophalangeal joints, attaching to the deep transverse metacarpal ligaments.

Several of the intrinsic muscles of the hand attach to the margins of the extensor hood on either side.

The extensor expansion consists of 3 parts/slips:

  • 1 Central part – inserts onto the base of the middle phalanx
  • 2 Lateral parts – pass laterally around the central part/slip and attach to the base of the distal phalanx


  • Extension of the index, middle, ring and little fingers at the metacarpophalangeal, proximal an distal interphalangeal joints
  • Extension of the wrist


Posterior interosseus nerve (continuation of the deep branch of the radial nerve)

Blood Supply

  • Posterior interosseus artery
  • Radial recurrent artery
  • Anterior interosseus artery


  • Flexor digitorum superficialis
  • Flexor digitorum profundus