Fibularis brevis muscle

At a glance

English

Fibularis brevis muscle

Latin (TA2)

Musculus fibularis brevis

System

Muscle

Region

Lower limb

Side

Paired, left and right

About the fibularis brevis muscle

Fibularis brevis, also called peroneus brevis, is the smaller of the two muscles of the lateral compartment of the leg. It lies deep to fibularis longus, against the fibula, and is the shorter of the pair. Both names come from the Greek word for a brooch pin, an old name for the slender fibula.

Its fibres come from the fibula's outer face over its lower two-thirds, on the inner side of the longus origin, and from the septa that part the lateral compartment from its anterior and posterior neighbours. The fibres run straight down to a tendon that passes behind the lateral malleolus. Here it lies directly on the bone, in front of the longus tendon, with both tendons in a shared groove and synovial sheath held by the superior fibular retinaculum. It then turns forwards along the outer surface of the calcaneus, above the fibular trochlea and the longus tendon, and ends on the tuberosity at the fifth metatarsal's base.

The muscle is the main evertor of the foot, turning the sole outwards, and it helps plantarflex the ankle a little. More important in everyday life is its steadying role: with fibularis longus it braces the outer side of the ankle, resisting the rolling-in that causes the common inversion sprain. When standing on one leg, both fibular muscles pull the leg towards the outer side of the foot and keep the body balanced over it.

In an inversion injury the tendon can pull hard enough to break off a fragment of the fifth metatarsal tuberosity, an avulsion fracture often seen with an ankle sprain; it is distinct from a Jones fracture a little further along the shaft. The tendon may also split lengthwise as it presses against the back of the fibula, or dislocate forwards over the malleolus if the retinaculum tears, giving pain and snapping behind the ankle. The muscle is supplied by the superficial fibular nerve.

Attachments, action and supply

Origin

Outer face of the fibula over its lower two-thirds, and the adjacent intermuscular septa.

Insertion

Tuberosity on the outer edge of the fifth metatarsal's base.

Action

Everts the foot and weakly plantarflexes the ankle; stabilises the lateral ankle.

Nerve supply

Superficial fibular nerve (L5, S1).

Blood supply

Branches of the fibular artery and the anterior tibial artery.