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The foot and ankle form a complex system of bones, joints, and ligaments, and muscles that work together to support the body and enable movement. One such movement is eversion, which is the tilting of the sole of the foot away from the midline. This movement is facilitated by the peroneus brevis muscle, also known as the fibularis brevis muscle, which originates from the lower two-thirds of the lateral fibula and inserts on the proximal fifth metatarsal. Additionally, the fibularis longus muscle also plays a role in plantarflexion and eversion of the foot.
| Characteristics | Values |
|---|---|
| Muscles that evert the foot | Peroneus brevis, fibularis brevis, fibularis longus, tibialis posterior |
| Other names | Peroneus brevis is also called the fibularis brevis muscle |
| Location | Lateral compartment of the lower extremity below the knee |
| Origin | Lower two-thirds of the lateral fibula |
| Insertion | Proximal fifth metatarsal |
| Nerve | Superficial peroneal nerve |
| Artery | Peroneal artery |
| Function | Evert the foot and plantarflex the ankle |
| Involvement in injuries | Most commonly dislocated tendon in the ankle |
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What You'll Learn
Peroneus brevis muscle
The Peroneus Brevis (also known as the Fibularis Brevis) is a short muscle that lies in the lateral part of the lower leg deep to the Fibularis Longus. It is one of three ankle everters, the others being the Fibularis Longus and the Fibularis Tertius. The Peroneus Brevis is the most commonly injured muscle during a lateral ankle sprain, and its tendon is the most commonly dislocated tendon in the ankle.
The Peroneus Brevis originates from the distal two-thirds of the lateral surface of the fibula and the adjacent part of the anterior intermuscular septum. Its tendon passes downwards and loops posterior to the lateral malleolus, then enters the lateral part of the foot. The tendon finally inserts on the styloid process of the proximal fifth metatarsal bone. The muscle belly of the Peroneus Brevis is found posterior to the extensor digitorum longus and Fibularis Tertius, and anterior to the Fibularis Longus, flexor hallucis longus, and the distal part of the soleus muscle.
The Peroneus Brevis is supplied by the superior and inferior branches of the anterior tibial artery, a branch of the popliteal artery, which is the distal continuation of the femoral artery. The tendon of the Peroneus Brevis and its accompanying muscle are supplied by an anastomotic network around the ankle, which 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.
The Peroneus Brevis crosses both the subtalar (talocalcaneal) and talocrural (ankle) joints and therefore contributes to the actions produced across these joints. The primary movements of the foot and ankle that the Peroneus Brevis assists with are plantar flexion, dorsiflexion, eversion, and inversion. Plantar flexion describes the movement of the foot down towards the sole, and dorsiflexion is moving the foot upwards towards the tibia. Eversion is tilting the sole away from the midline, and inversion is tilting the sole towards the midline.
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Fibularis longus
The fibularis longus (also known as peroneus longus) is a muscle in the lateral compartment of the leg. It is the longest and most superficial of the three fibularis (or peroneus) muscles. The fibularis longus is attached at its upper end to the head of the fibula, with its "belly" running down along most of this bone. The muscle then becomes a tendon that wraps around and behind the lateral malleolus of the ankle.
The fibularis longus plays a role in two movements of the foot and ankle: eversion and plantar flexion. Eversion refers to the tilting of the sole of the foot away from the midline of the body. The fibularis longus is one of four muscles responsible for this action. The other three are the fibularis brevis, tibialis anterior, and tibialis posterior. The fibularis longus also contributes to plantar flexion, which is the extension of the foot downward and away from the body at the ankle. This movement is also facilitated by the fibularis brevis and the tibialis posterior.
The fibularis longus is supplied by the superficial fibular nerve, which arises from the fifth lumbar and first sacral roots of the spinal cord. The tendon of the fibularis longus runs behind the lateral malleolus of the ankle in a groove shared with the tendon of the fibularis brevis. This groove is converted into a canal by the superior fibular retinaculum, and the tendons within it are contained in a common mucous sheath.
The fibularis longus is susceptible to various pathologies, including contracture or shortening, which can result in an everted or valgus foot. Tears in the fibularis longus tendon are also common, typically occurring longitudinally due to subluxation over the fibula but sometimes presenting as transverse tears. Avulsion fractures can also occur as a result of tendon tears. Peroneal tenosynovitis is another pathological condition affecting the fibularis longus, characterised by fluid accumulation within the tendon sheath and associated with sports participation.
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Fibularis brevis
The fibularis brevis, also known as the peroneus brevis, is a short muscle located in the lateral part of the lower leg, deep to the fibularis longus. It is one of three ankle everters, collectively called the fibularis muscles, that include the fibularis longus, fibularis brevis, and fibularis tertius. The fibularis brevis is the strongest abductor of the foot and is responsible for 63% of the power needed to evert the foot. It also assists in plantar flexion, which is the movement of the foot down towards the sole.
The fibularis brevis originates from the lower or distal two-thirds of the lateral surface of the fibula and the adjacent part of the anterior intermuscular septum. Its muscle fibres course inferomedially along the lateral border of the fibula, forming a fusiform muscle belly. At the distal third of the leg, the fibularis brevis gives off a broad, flat tendon that courses deep to the tendon of the fibularis longus proximally and anterior to the same structure in its distal aspect. The tendon then continues caudally, passing behind the lateral malleolus to enter the lateral part of the foot.
The tendon of the fibularis brevis inserts on the fifth metatarsal bone, posterior to the insertion of the fibularis tertius muscle. The fibularis brevis receives innervation from the superficial peroneal or fibular nerve, and its arterial supply is by muscular branches of the peroneal or fibular artery. The superior and inferior peroneal retinacula secure the tendons of the fibularis brevis and longus in place at the level of the ankle, preventing tendon subluxation.
Injuries to the fibularis brevis commonly affect the tendon, including tendinopathy, dislocation or subluxation, sprain, or splitting. Lateral ankle sprains can cause the fibularis brevis to tear and result in swelling at the lateral ankle. During a supination-adduction injury, the tendon of the fibularis brevis may be injured and pull at the base of the fifth metatarsal, causing an avulsion fracture known as a Jones fracture.
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Tibialis posterior
The tibialis posterior muscle is located deep in the posterior compartment of the lower leg, between the flexor digitorum longus and the flexor hallucis longus. It is the deepest muscle in this compartment and the most central of all the leg muscles. The tibialis posterior is a key stabilising muscle, supporting the medial arch of the foot. It is also a primary inverter of the foot, causing inversion at the midtarsal and subtalar joints.
The tibialis posterior muscle originates on the inner posterior border of the fibula and is attached to the interosseous membrane, which connects to the tibia and fibula. The tendon of the tibialis posterior muscle, also called the posterior tibial tendon, travels distally and then posterior to the medial malleolus, along with the tendons of the flexor digitorum longus, the posterior tibial artery, the tibial nerve, and the flexor hallucis longus.
Once the tendon passes the medial malleolus, it moves along the plantar aspect of the foot, splitting into three components: primary, plantar, and recurrent. The main portion inserts onto the navicular bone tubercle, while the plantar sections attach to the medial cuneiform, the base of the second, third, and fourth metatarsals, the second and third cuneiform, and the cuboid. The recurrent portion has a small insertion site at the sustentaculum tali of the calcaneus.
The tibialis posterior is responsible for plantar flexion and inversion of the foot. It receives its arterial blood supply from the posterior tibial artery and innervation from the tibial nerve. Dysfunction of the tibialis posterior can lead to flat feet in adults, as the muscle plays a vital role in supporting the arch of the foot. Strengthening exercises can be done to improve arch control and prevent or treat conditions associated with weakness in this muscle.
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Subtalar joint
The subtalar joint is a joint of the foot that occurs at the meeting point of the talus and the calcaneus. The subtalar joint is formed between two of the tarsal bones: the inferior surface of the body of the talus and the superior surface of the calcaneus. The joint is classed structurally as a synovial joint and functionally as a plane synovial joint or a plane joint. The talus is oriented slightly obliquely on the anterior surface of the calcaneus.
The subtalar joint is enclosed by a joint capsule, which is lined internally by a synovial membrane and strengthened externally by a fibrous layer. The capsule is also supported by three ligaments, with an additional ligament—the interosseous talocalcaneal ligament—that acts to bind the talus and calcaneus together. The subtalar joint is formed on an oblique axis and is, therefore, the chief site within the foot for the generation of eversion and inversion movements. The ligaments around the subtalar joint can be distinguished as intrinsic (cervical ligament, interosseous talocalcaneal ligament) and extrinsic ligaments (calcaneo-fibular ligament, tibio-calcaneal part of the deltoid ligament).
The subtalar joint has a complex anatomy that can vary significantly between individuals. Movement is affected by several adjacent joints, ligaments, and periarticular tendons. The centre of rotation of the subtalar joint is thought to be in the region of the middle facet. It is considered a gliding joint, acting as a hinge connecting the talus and calcaneus. There is extensive variation in the inclination from horizontal. The subtalar joint can also be considered a combination of the anatomic subtalar joint and the talocalcaneal part of the talocalcaneonavicular joint. When both of these articulations are accounted for together, it allows for pronation and supination of the midfoot to occur.
The subtalar joint is particularly susceptible to arthritis, and symptoms include pain when walking, loss of motion through the joint's range of motion, and difficulty walking on uneven surfaces. The joint is usually disrupted in cases of calcaneal fracture, causing the joint to become arthritic.
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Frequently asked questions
Eversion of the foot is the movement of the sole of the foot away from the midline of the body.
The opposite movement of eversion is inversion, which is the movement of the sole of the foot towards the midline of the body.
The peroneus brevis muscle, also known as the fibularis brevis muscle, is responsible for everting the foot.
The peroneus brevis muscle partially forms the lateral compartment of the leg, along with the peroneus longus muscle. It originates from the lower two-thirds of the lateral fibula and inserts on the proximal fifth metatarsal.
Yes, the fibularis longus (or peroneus longus) and the tibialis posterior muscles are also involved in the eversion of the foot.
