The extensor digiti minimi is one of the muscles of the superficial layer of the posterior compartment of the forearm. It is an accessory extensor of the little finger.

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.

Origin
  • Lateral epicondyle of the humerus
  • Intermuscular septa of adjacent muscles
Insertion
  • Extensor expansion of little finger

The extensor expansion/hood is 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 attach 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, reinforcing the structure.

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
Innervation
  • Posterior interosseus nerve (continuation of the deep branch of the radial nerve)
Blood Supply
  • Posterior interosseus artery
  • Radial recurrent artery
  • Anterior interosseus artery
Antagonist

Flexor digiti minimi brevis

Action
  • Extension of the little finger at the metacarpophalangeal joint (primarily) as well as at the proximal and distal interphalangeal joints
  • Extension of the wrist