Extensor digitorum longus: extension of the lateral four toes
Extensor digitorum longus (its name means the long extensor of the digits) mainly extends the lateral four toes and only assists dorsiflexion, which lifts the foot upwards at the ankle.
Remember
Extensor digitorum longus mainly extends the lateral four toes, the second to fifth, while the great toe has its own extensor; dorsiflexion is only its secondary role.
Extensor digitorum longus (its name means the long extensor of the digits) belongs to the anterior compartment, the muscles lying beside the shin at the front of the leg. It begins on the upper tibia and the fibula, and on the interosseous membrane, a tough sheet joining the two leg bones.
Its tendon runs along the dorsal surface (the top of the foot) and splits into four. One part goes to each of the lateral four toes, the second to fifth. Pulling on those tendons straightens and lifts the toes, which is extension. The great toe (the hallux) is the exception, because its extension belongs to extensor hallucis longus.
The muscle also helps with dorsiflexion, which means lifting the foot upwards at the ankle. That is a supporting role, because tibialis anterior is the strongest dorsiflexor. The opposite movement, plantarflexion, points the foot downwards and comes from the posterior compartment (the calf).
The deep fibular nerve, the nerve of those front muscles, supplies the anterior compartment. An injury to that nerve before it branches to supply the anterior compartment muscles therefore produces a combined pattern of weak dorsiflexion and weak toe extension.
Key facts
- Main action
- extension of the lateral four toes, the second to fifth.
- Assisting action
- dorsiflexion of the ankle, led by tibialis anterior.
- Tendons
- its tendon splits into four, one for each of the lateral four toes.
- Compartment and nerve
- the anterior compartment of the leg, supplied by the deep fibular nerve.
- Great toe
- extension of the hallux belongs to extensor hallucis longus, not to this muscle.
- Palpation
- the four tendons can be felt on the top of the foot, which is its dorsal surface.
Exam traps
- Dorsiflexion is only a secondary role of extensor digitorum longus, because tibialis anterior is the strongest dorsiflexor and the main action of the muscle is on the toes.
- Extensor hallucis longus, not extensor digitorum longus, extends the great toe, because extensor digitorum longus serves the lateral four toes.
- Flexion (bending) of the lateral four toes is the opposite of extension, and flexor muscles such as flexor digitorum longus in the posterior compartment produce it, not an extensor of the anterior compartment.
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