Extensor digiti minimi

At a glance

English

Extensor digiti minimi

Latin (TA2)

Extensor digiti minimi

System

Muscle

Region

Upper limb

Side

Paired, left and right

About the extensor digiti minimi

Extensor digiti minimi is a thin muscle in the superficial layer of the posterior forearm. It lies on the ulnar side of extensor digitorum and is often partly joined to it, so it can look like a detached slip of that larger muscle.

Its fibres start from the shared extensor tendon on the lateral epicondyle on the humerus and from the fibrous septa it shares with its neighbours. The narrow belly runs down the forearm and becomes a tendon that passes under the extensor retinaculum in its own compartment, the fifth, lying over the distal radioulnar joint. On the back of the hand the tendon frequently splits in two. Its slips join the tendon of extensor digitorum for the little finger on the ulnar side and merge into the extensor expansion over the proximal phalanx.

The muscle extends the little finger at the metacarpophalangeal joint and, through the extensor expansion and with help from the small hand muscles, at the interphalangeal joints. It lets the little finger be raised on its own, which matters in typing and playing instruments, and it adds a little to wrist extension. Its nerve is the posterior interosseous nerve, the deep continuation of the radial nerve, and its blood comes mainly from the posterior interosseous artery.

Since the extensor digitorum slip to the little finger is often thin or missing, this muscle may be the main extensor of that digit. Its tendon is sometimes used for tendon transfer. Rheumatoid disease at the distal radioulnar joint can wear through the tendon, and loss of little finger extension is often the first sign.

Attachments, action and supply

Origin

Lateral humeral epicondyle through the common extensor tendon, and the adjoining intermuscular septa.

Insertion

Extensor expansion of the little finger, joining the extensor digitorum tendon to that finger.

Action

Extends the little finger at the metacarpophalangeal and interphalangeal joints; assists wrist extension.

Nerve supply

Posterior interosseous nerve (C7, C8).

Blood supply

Posterior interosseous artery.