Fibularis brevis muscle

Origin and insertion

Fibularis brevis originates from the distal two-thirds of the lateral surface of fibula and the adjacent part of the anterior intermuscular septum. The muscle fibers course inferomedially along the lateral border of fibula, comprising a fusiform muscle belly.

At the level of the distal third of the leg, fibularis brevis gives off a broad flat tendon. The tendon courses deep to the tendon of fibularis longus proximally, and anterior to the same structure in its distal aspect. It then continues caudally to pass behind the lateral malleolus to enter the lateral part of the foot. The tendon of fibularis brevis finally inserts on the tuberosity of 5th metatarsal bone, posterior to the insertion of fibularis tertius muscle.

Relations 

The muscle belly of fibularis brevis is found posterior to the extensor digitorum longus and fibularis tertius, while it sits anterior to the fibularis longus, flexor hallucis longus and distal part of the soleus muscle. The distal portion of the sural nerve runs between the deep surface of fibularis brevis and anterior surface of soleus muscle.

The tendon of fibularis brevis initially runs anterior to the tendon of fibularis longus as they pass posterior to the lateral malleolus. The tendons of these muscles then enter separate osteofibrous canals limited medially by the calcaneus and laterally by the inferior fibular retinaculum. They take on a horizontal course as they pass behind the lateral malleolus such that fibularis brevis tendon is now superior to the fibularis longus tendon, and both are inferolateral to the lateral border of extensor digitorum brevis. 

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Innervation

Motoric innervation to the fibularis brevis muscle is provided by the superficial fibular (peroneal) nerve (L5-S1). This is a branch of the common fibular division of sciatic nerve. Cutaneous innervation to the skin overlying this muscle is mitigated by the spinal nerve roots L5, S1 and 2.

Blood supply 

Fibularis brevis and the other muscles of the lateral compartment of the leg are supplied by the superior and inferior branches of anterior tibial artery. This is a branch of the popliteal artery, which is the distal continuation of the femoral artery. On rare occasions, the chief blood supply to the lateral compartment is the fibular artery, which is a branch of the tibial artery.

The tendon of fibularis brevis and its accompanying muscle is supplied by an anastomotic network around the ankle. The network includes the arcuate, anterior lateral malleolar, fibular perforating, lateral calcaneal, lateral and medial plantar and lateral tarsal arteries. The venous blood from this muscle is conveyed by the anterior tibial vein.

Functions

Fibularis brevis crosses both the subtalar (talocalcaneal) and talocrural (ankle) joints and therefore contributes to the actions produced across these joints. The main function of fibularis brevis is to evert the foot at the subtalar joint, which helps to restore the foot to its anatomical position after it has been inverted. This is particularly important when running or walking on uneven terrain.

Since fibularis brevis counteracts inversion of the foot, it may also prevent the body from falling to the opposite side when the individual is balancing on one leg. The muscle also causes plantarflexion of the foot at the ankle joint while it is everting it. 

There are a lot of supporting structures that help to carry out the daily functions of the ankle joint. Check out the learning materials below to learn more about them.