Extensor digitorum longus

At a glance

English

Extensor digitorum longus

Latin (TA2)

Extensor longus digitorum

System

Muscle

Region

Lower limb

Side

Paired, left and right

Arises from

The fibula

Inserts on

The distal phalanx of fifth finger of foot, distal phalanx of fourth finger of foot, distal phalanx of third finger of foot and middle phalanx of fifth finger of foot

About the extensor digitorum longus

Extensor digitorum longus lies in the anterior compartment of the leg, on the lateral side of tibialis anterior and in front of the fibula. It is a pennate muscle: its fibres slant onto a tendon running down the front of the belly. With fibularis tertius, which is often regarded as its fifth slip, it makes up the outer half of the anterior compartment.

Its origin is long. It takes fibres from the lateral tibial condyle, from most of the front surface of the fibular shaft above, from the upper interosseous membrane and from the deep fascia and the septa it shares with its neighbours. In the upper leg the anterior tibial vessels and the deep fibular nerve run between it and tibialis anterior. The tendon runs beneath both extensor retinacula, upper and lower, at the front of the ankle, in one synovial sheath with fibularis tertius, and splits into slips for the second to fifth toes.

On each toe the slip spreads into an extensor expansion over the proximal phalanx, joined on the outer side, for the second to fourth toes, by a tendon of extensor digitorum brevis, and receiving fibres from the lumbricals and interossei. Over the proximal interphalangeal joint the expansion divides into three bands: a central one to the base of the middle phalanx, and two side bands that reunite and end on the base of the distal phalanx. The arrangement mirrors the extensor apparatus of the fingers.

The muscle straightens the lesser toes at all their joints and dorsiflexes the foot at the ankle, and it helps evert the foot. In walking it lifts the toes and foot clear of the ground during swing. Weakness from injury to the common or deep fibular nerve contributes to foot drop. Its slips vary often, with doubled tendons or extra bands to metatarsals or neighbouring muscles.

Attachments, action and supply

Origin

Lateral condyle of the tibia, upper three-quarters of the front of the fibula, upper interosseous membrane, deep fascia and intermuscular septa.

Insertion

Middle and distal phalanges of the second to fifth toes, through their extensor expansions.

Action

Extends the lesser toes, dorsiflexes the foot at the ankle and helps evert it.

Nerve supply

Deep fibular nerve (L5, S1).

Blood supply

Anterior tibial artery.