Quadratus plantae muscle

At a glance

English

Quadratus plantae muscle

Latin (TA2)

Musculus quadratus plantae

System

Muscle

Region

Lower limb

Side

Paired, left and right

About the quadratus plantae muscle

Quadratus plantae, also called flexor accessorius, is a flat muscle in the second layer of the sole, at the back half of the foot. It lies deep to flexor digitorum brevis, with the lateral plantar nerve and vessels running between the two as they cross the foot. It has no counterpart in the hand, reflecting the special demands placed on the foot.

It begins by two heads from the calcaneus, with the long plantar ligament between them. Of these, the medial head is larger and fleshy and comes from the concave inner surface of the heel bone, beneath the groove for the flexor hallucis longus tendon. The lateral head is flat and tendinous and arises from the outer edge of the calcaneal undersurface, ahead of its lateral process, with extra fibres off the long plantar ligament. The heads converge at a sharp angle onto a flat band that attaches to the outer border and surfaces of the flexor digitorum longus tendon, just where it divides, often sending slips to the tendons for the second to fourth toes.

The long flexor tendon enters the sole from behind the medial malleolus and so pulls at an angle towards the inner side. By tugging backwards along the line of the foot, quadratus plantae straightens that pull so the lesser toes flex directly. It also lets the toes keep flexing when flexor digitorum longus is slack, as when the ankle is fully plantarflexed, helping the toes grip during walking and standing.

It is supplied by the lateral plantar nerve, a branch of the tibial nerve, and by the lateral plantar artery. The muscle varies widely: the lateral head is often absent, the whole muscle may be missing, and the number of tendons receiving its fibres differs between people. Its neighbouring nerve may be compressed near the heel and is one cause of persistent heel pain.

Attachments, action and supply

Origin

Medial head: medial surface of the calcaneus; lateral head: lateral border of the plantar surface of the calcaneus and the long plantar ligament.

Insertion

Lateral margin and surfaces of the flexor digitorum longus tendon, often with slips to its tendons for the second to fourth toes.

Action

Corrects the oblique pull of flexor digitorum longus and assists flexion of the second to fifth toes.

Nerve supply

Lateral plantar nerve (S1, S2, S3).

Blood supply

Lateral plantar artery, with branches of the medial plantar artery.