Extensor hallucis longus

At a glance

English

Extensor hallucis longus

Latin (TA2)

Extensor longus hallucis

System

Muscle

Region

Lower limb

Side

Paired, left and right

About the extensor hallucis longus

Extensor hallucis longus lies in the anterior compartment of the leg, deep between tibialis anterior on its inner side and extensor digitorum longus on its outer side. In the upper leg it is hidden by these two; only in the lower third does it come to the surface. Its tendon is the prominent cord seen on top of the foot when the big toe is lifted.

It arises from the middle half of the front surface of the fibula, medial to extensor digitorum longus, and from the interosseous membrane next to it. Between this muscle and tibialis anterior lie the deep fibular nerve and anterior tibial vessels. The fibres end on a tendon along the front edge of the muscle. This passes under the superior extensor retinaculum and through its own tunnel in the inferior retinaculum, crossing the anterior tibial vessels from outside to inside near the ankle, and runs along the inner dorsum of the foot to the base of the big toe's distal phalanx. Near the metatarsophalangeal joint it sends thin expansions over the joint and often a slip to the proximal phalanx.

The muscle extends the big toe at both of its joints and dorsiflexes the foot at the ankle. Its effect on inversion and eversion is small and depends on the foot's position. In walking it lifts the big toe and the front of the foot during swing, and at heel strike it helps lower the foot under control.

Testing its strength by asking the patient to lift the big toe against resistance checks the L5 root and the deep fibular nerve; weakness is an early sign of an L5 disc problem or fibular nerve damage. At the ankle the dorsalis pedis pulse is felt just lateral to its tendon. The tendon can be cut by falling glass or knives on the top of the foot and then needs repair.

Attachments, action and supply

Origin

Middle half of the fibula's front surface and the adjacent interosseous membrane.

Insertion

Base of the big toe's distal phalanx, with a slip often to the proximal phalanx.

Action

Extends the big toe and dorsiflexes the foot at the ankle; slight effect on inversion and eversion.

Nerve supply

Deep fibular nerve (L5, S1).

Blood supply

Anterior tibial artery.