Muscles everting the foot

Peroneus longus

Peroneus brevis

Peroneus tertius

Peroneus brevis

Peroneus brevis is also situated on the lateral side of the leg enclosed in the same osteofascial compartment. It arises from the lower two-thirds of the lateral surface of the fibula, the upper half being anterior to peroneus longus. It also attaches to the intermuscular septa at all sides.

The muscle belly is fusiform and short, soon passing into a tendon which accompanies that of peroneus longus to pass behind the lateral malleolus in a common synovial sheath. The tendon then passes forwards and downwards into a groove above the peroneal tubercle of the calcaneus, which is converted into a tunnel by the inferior part of the peroneal retinaculum. It then passes forward to its insertion into the tubercle on the lateral side of the base of the fifth metatarsal. Above the tubercle, the tendon is surrounded by a synovial sheath, which is separated from that of peroneus longus. A slip from the tendon usually joins the long extensor to the little toe. Other separate slips may join peroneus longus, or pass to the calcaneus or cuboid.

Nerve supply

Peroneus brevis is supplied by the superficial peroneal nerve, root value L5, S1. The skin covering the muscle is innervated by L5, S1, 2.

Action

Peroneus brevis is an evertor of the foot. Because of its course and attachments, the pull of its tendon is in such a direction to produce plantarflexion of the ankle at the same time. 

Functional activity

This muscle is also well-positioned to prevent sideways sway in the standing position. In standing on one leg, it will help to prevent the body falling to the opposite side, thus working with a reversed origin and insertion. In walking or running, especially over the rough ground, it plays an important role in controlling the position of the foot and should prevent the foot from becoming too inverted. In many cases, however, this mechanism does not always appear to work correctly, and the foot over-inverts causing the weight to come down on the lateral side of the foot forcing the foot into further inversion. This can severely damage or even snap the tendon of the muscle and often the anterior talofibular ligament of the ankle joint.

Palpation

If the fingers are placed on the belly of peroneus longus and then moved downwards to the lower half of the fibula (but in the same vertical line), the belly of peroneus brevis can be palpated when the foot is everted and plantarflexed. Its tendon can easily be traced to the groove just above the peroneal tubercle and then forwards to its insertion into the tubercle of the fifth metatarsal.