Fibularis brevis muscle
Fibularis brevis, or peroneus brevis, is a short muscle that together with the fibularis (peroneus) longus comprises the group of the lateral leg muscles.
Based on their function, both peroneal muscles belong to a larger group of leg muscles whose common function is to plantarflex the foot (point the toes downward). Other muscles of this group are the gastrocnemius, soleus, plantaris, tibialis posterior, fibularis tertius, flexor digitorum longus, and flexor hallucis longus. Besides plantarflexing the foot, fibularis brevis and longus also evert the foot while contracting.
|Origin||Distal 2/3 of the lateral surface of fibula, anterior inermuscular septum|
|Insertion||Tuberosity of the 5th metatarsal bone|
|Action||Talocrural joint: Foot plantar flexion
Subtalar joint: Foot eversion
|Innervation||Superficial fibular nerve (L5, S1)|
|Blood supply||Anterior tibial artery|
This article will discuss the anatomy and function of the 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.
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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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.
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.
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.
The location of the fibularis brevis tendon renders it susceptible to injury. Over time, it is exposed to shear stress while gliding between the lateral malleolus and the tendon of fibularis longus. If the foot becomes over-inverted, the excess downward force will be applied to the lateral part of the foot, causing tears or rupture of fibularis brevis tendon. These injuries are seen among basketball, tennis and football (NFL) players. If the tendon of fibularis brevis ruptures, it can also cause an avulsion fracture of the fifth metatarsal tuberosity.
Microtears in the fibularis brevis tendon can over time result in fibular (peroneal) tendonitis. This is often characterized by pain and swelling to the posterolateral part of the ankle and foot. The pain is indolent and worsens with exertion. Acute management of this problem involves resting the limb, applying ice packs to the affected area, compression bandage of the ankle and elevation of the limb. Non-steroidal anti-inflammatory drugs can also aid in alleviating the pain.
Physiotherapists recommend that individuals perform adequate stretching prior to starting strenuous activities. This helps to promote collagen synthesis and muscle fiber organization, thus strengthening the muscle. One way to stretch the fibularis muscles is to manually invert and evert the foot. This can be done by sitting on a chair with the leg resting on the opposite knee and holding the foot in the opposite hand. Now slowly twist the sole of the foot toward the floor (eversion) then back toward the ceiling (inversion). Another technique involves sitting with the lower limbs parallel to the floor, wrapping a towel around the toes and pulling the foot into dorsiflexion and inversion. The fibularis muscles will inadvertently be activated and stretched in an attempt to counteract the action described.
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