Extensor digitorum

At a glance

English

Extensor digitorum

Latin (TA2)

Extensor digitorum

System

Muscle

Region

Upper limb

Side

Paired, left and right

Inserts on

The middle phalanx of fifth finger of hand, middle phalanx of fourth finger of hand, middle phalanx of second finger of hand, middle phalanx of third finger of hand, proximal phalanx of fourth finger of hand, proximal phalanx of second finger of hand and proximal phalanx of third finger of hand

About the extensor digitorum

Extensor digitorum forms much of the bulk of the superficial posterior forearm, lying between the radial wrist extensors and extensor digiti minimi. It is the muscle that straightens the fingers when the hand is opened.

It arises from the common extensor tendon on the lateral epicondyle on the humerus, from the deep fascia and from the septa between it and its neighbours. Towards the lower forearm the belly divides into four tendons, which pass under the extensor retinaculum in the fourth compartment together with extensor indicis. Across the dorsum of the hand these tendons fan out to the index, middle, ring and little fingers, and oblique bands called intertendinous connections link them near the knuckles. Over each metacarpophalangeal joint the tendon widens into an extensor expansion. A central slip attaches to the base of the middle phalanx and two lateral bands, joined by the lumbricals and interossei, reunite to reach the base of the distal phalanx; some fibres also attach to the proximal phalanx.

The muscle extends the fingers mainly at the metacarpophalangeal joints and, with the small hand muscles, at the interphalangeal joints. It also helps extend the wrist and tends to spread the fingers as they straighten. The linking bands explain why the ring finger is hard to lift on its own. It is supplied by the posterior interosseous nerve and by the posterior interosseous artery, with help from the radial recurrent artery.

Damage to the extensor mechanism gives typical finger deformities. Tearing of the insertion at the distal phalanx causes mallet finger, while damage to the central slip can lead to a boutonniere deformity.

Attachments, action and supply

Origin

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

Insertion

Extensor expansions of the index, middle, ring and little fingers, reaching the middle phalanges by a central slip and the distal phalanges by lateral bands.

Action

Extends the medial four fingers at the metacarpophalangeal and interphalangeal joints; assists wrist extension.

Nerve supply

Posterior interosseous nerve (C7, C8).

Blood supply

Posterior interosseous artery, with branches from the radial recurrent artery.