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:
- Extensor carpi radialis longus
- Extensor carpi radialis brevis
- Extensor digitorum
- Extensor digiti minimi
- Extensor carpi ulnaris
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.
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:
Posterior interosseus nerve (continuation of the deep branch of the radial nerve)