Fibularis Brevis

The fibularis brevis, also known as peroneus brevis, is a muscle of the lateral compartment of the leg. It lies deep to fibularis longus and extends from the distal portion of the fibula to the base of the fifth metatarsal. Its principal action is eversion of the foot, and it also assists plantarflexion at the ankle.^[1][2]

The muscle becomes tendinous in the distal leg. Its tendon passes posterior to the lateral malleolus with the tendon of fibularis longus and then travels along the lateral side of the foot to insert on the prominent tuberosity at the base of the fifth metatarsal.

Fibularis brevis is supplied by the superficial fibular nerve. Its location, tendon course, and fifth metatarsal attachment are clinically important in lateral ankle injuries, fibular tendon disorders, and avulsion fractures of the fifth metatarsal.

Location

Fibularis brevis occupies the lateral compartment of the leg. It lies deep to fibularis longus through most of its course and is closely related to the lateral surface of the fibula.

The muscle belly is situated predominantly in the middle and distal portions of the leg. Distally, it becomes a tendon that passes behind the lateral malleolus.

After leaving the retromalleolar region, the tendon travels anteriorly along the lateral aspect of the foot toward the base of the fifth metatarsal.

General Anatomy

Feature	Anatomy
Muscle	Fibularis brevis
Alternative name	Peroneus brevis
Compartment	Lateral compartment of leg
Origin	Distal lateral surface of fibula and adjacent intermuscular septa
Insertion	Tuberosity at base of fifth metatarsal
Innervation	Superficial fibular nerve
Root values	L5, S1, S2
Principal action	Eversion of foot
Secondary action	Assists plantarflexion of ankle

Origin

Fibularis brevis arises primarily from the distal two-thirds of the lateral surface of the fibula.^[1][3]

Additional fibers arise from the adjacent anterior and posterior intermuscular septa. These septa help separate the lateral compartment from the anterior and posterior compartments of the leg.

The proximal part of the muscle lies deep to fibularis longus, which has a more extensive proximal origin from the fibula.

Insertion

The tendon of fibularis brevis inserts onto the tuberosity at the base of the fifth metatarsal.

This prominent bony attachment can be palpated along the lateral border of the foot. The insertion provides fibularis brevis with an effective lateral line of pull for eversion.

The attachment should be distinguished from that of fibularis tertius, which inserts more dorsally on the base and proximal shaft of the fifth metatarsal.

Course

Fibularis brevis descends along the lateral surface of the fibula and becomes tendinous in the distal leg.

The tendon passes posterior to the lateral malleolus, where it shares a fibro-osseous pathway with the fibularis longus tendon. Within this region, the fibularis brevis tendon generally lies anterior to the fibularis longus tendon.

After passing around the lateral malleolus, the tendon continues anteriorly along the lateral side of the calcaneus and foot before reaching the fifth metatarsal.

Lateral Compartment of the Leg

The lateral compartment contains two principal muscles:

• Fibularis longus
• Fibularis brevis

Both muscles are supplied by the superficial fibular nerve and act primarily as evertors of the foot.

The lateral compartment is separated from the anterior and posterior compartments by intermuscular septa and the surrounding deep fascia of the leg.

Relationship to Fibularis Longus

Fibularis longus lies superficial to fibularis brevis in much of the lateral compartment. The two muscles share similar actions and innervation but have markedly different distal courses and insertions.

Both tendons pass behind the lateral malleolus. Fibularis brevis then travels toward the fifth metatarsal, while fibularis longus continues beneath the foot toward the medial cuneiform and first metatarsal.

Feature	Fibularis Brevis	Fibularis Longus
Position in lateral compartment	Deeper	More superficial
Insertion	Base of fifth metatarsal	Base of first metatarsal and medial cuneiform
Primary action	Eversion	Eversion
Ankle action	Weak plantarflexion	Weak plantarflexion
Innervation	Superficial fibular nerve	Superficial fibular nerve

Relationship to Fibularis Tertius

Fibularis brevis and fibularis tertius both attach near the base of the fifth metatarsal and both contribute to eversion, but they belong to different muscular compartments.

Fibularis brevis lies in the lateral compartment and is supplied by the superficial fibular nerve. Fibularis tertius lies in the anterior compartment and is supplied by the deep fibular nerve.

Their actions at the ankle also differ. Fibularis brevis assists plantarflexion, while fibularis tertius assists dorsiflexion.

Relationship to the Fibula

The fibula provides the principal origin of fibularis brevis. The muscle arises from its lateral surface and descends closely applied to the bone.

The fibula also provides attachment for the intermuscular septa that help define the lateral compartment.

Near the ankle, the distal fibula expands to form the lateral malleolus, around which the fibularis brevis tendon changes direction.

Relationship to the Lateral Malleolus

The fibularis brevis tendon passes immediately posterior to the lateral malleolus. The malleolus therefore functions as a pulley that redirects the tendon toward the lateral foot.

The tendon is retained in this position by the superior fibular retinaculum. Distal to the malleolus, the tendon continues beneath the inferior fibular retinaculum.

The retromalleolar position of the tendon is clinically important because lateral ankle trauma can affect both the tendon and its retaining structures.

Fibular Retinacula

The tendons of fibularis longus and fibularis brevis are stabilized around the lateral ankle by the superior and inferior fibular retinacula.

The superior fibular retinaculum holds the tendons within the groove posterior to the lateral malleolus. The inferior fibular retinaculum secures the tendons more distally along the lateral calcaneal region.

These retinacula prevent excessive displacement and bowstringing of the tendons during ankle and foot movement.

Fibular Tendon Sheaths

The fibularis longus and brevis tendons are surrounded by synovial sheaths as they pass through the retromalleolar region.

These sheaths reduce friction as the tendons repeatedly glide around the posterior surface of the lateral malleolus.

Inflammation of the tendon sheaths can contribute to pain and swelling along the posterolateral ankle.

Relationship Between the Fibular Tendons

Behind the lateral malleolus, the tendon of fibularis brevis generally lies anterior to the tendon of fibularis longus.

As the tendons continue distally, their courses diverge. Fibularis brevis remains relatively superficial and travels toward the fifth metatarsal, while fibularis longus passes farther inferiorly and eventually enters the plantar aspect of the foot.

This arrangement is useful when identifying the tendons on cross-sectional imaging or during surgery.

Relationship to the Calcaneus

After passing behind the lateral malleolus, the fibularis brevis tendon courses along the lateral surface of the calcaneus.

The fibular trochlea, when prominent, helps separate the paths of the fibular tendons. Fibularis brevis typically passes superior to this bony prominence, while fibularis longus passes inferior to it.

The tendons are maintained against the calcaneus by the inferior fibular retinaculum.

Relationship to the Fifth Metatarsal

The insertion of fibularis brevis onto the fifth metatarsal tuberosity is one of its most important anatomical relationships.

The tuberosity projects laterally from the base of the fifth metatarsal and can be palpated through the skin.

Force transmitted through the fibularis brevis tendon can contribute to avulsion of this region during sudden inversion injuries.

Superficial Fibular Nerve

Fibularis brevis is innervated by the superficial fibular nerve, a terminal branch of the common fibular nerve.

The superficial fibular nerve descends within the lateral compartment and supplies both fibularis longus and fibularis brevis.

In the distal leg, it pierces the deep fascia and becomes primarily cutaneous, supplying much of the skin on the dorsum of the foot.

Innervation

The motor supply to fibularis brevis is provided by the superficial fibular nerve, with root contributions commonly described as L5, S1, and S2.

The nerve arises from the common fibular nerve after it passes around the proximal fibula.

Because both lateral compartment muscles share this nerve supply, injury to the superficial fibular nerve can weaken eversion of the foot.

Blood Supply

Fibularis brevis receives arterial blood primarily from branches of the fibular artery, with contributions from neighboring arterial networks.

The fibular artery arises from the posterior tibial artery and descends within the posterior region of the leg near the fibula.

Perforating and muscular branches reach structures associated with the lateral compartment and lateral ankle.

Actions

Eversion

The principal action of fibularis brevis is eversion of the foot. Its tendon passes along the lateral side of the ankle and inserts on the lateral border of the foot.

Contraction therefore elevates the lateral border of the foot and turns the plantar surface away from the midline.

Fibularis brevis works primarily with fibularis longus, while fibularis tertius and extensor digitorum longus can provide additional evertor force.

Plantarflexion

Fibularis brevis assists plantarflexion of the ankle because its tendon passes posterior to the transverse axis of the talocrural joint.

Its plantarflexion force is substantially weaker than that of gastrocnemius and soleus.

Its position nevertheless allows it to assist the larger plantarflexors during movements requiring combined plantarflexion and eversion.

Functional Opposition to Invertors

Fibularis brevis acts in opposition to strong invertors such as tibialis anterior and tibialis posterior.

Balanced activity between these muscle groups helps maintain the foot in an appropriate position during standing, walking, and changes in direction.

The fibular muscles are particularly important for dynamically resisting excessive inversion of the foot.

Role During Walking

During gait, fibularis brevis contributes to control of the lateral side of the foot and helps regulate inversion and eversion as body weight passes over the supporting limb.

Its activity works with fibularis longus and other muscles to stabilize the foot against changing ground-reaction forces.

During uneven-surface walking, rapid activation of the evertors can help correct unwanted inversion and maintain lateral ankle stability.

Role in Lateral Ankle Stability

Fibularis brevis contributes to dynamic lateral ankle stability. Its evertor action opposes excessive inversion, the movement involved in many common lateral ankle sprains.

This muscular stabilization complements the passive support provided by the lateral ligament complex of the ankle.

Normal neuromuscular control of the fibular muscles is therefore important for maintaining ankle stability during rapid or unpredictable movements.

Comparison with Fibularis Longus and Tertius

Feature	Fibularis Brevis	Fibularis Longus	Fibularis Tertius
Compartment	Lateral	Lateral	Anterior
Innervation	Superficial fibular nerve	Superficial fibular nerve	Deep fibular nerve
Insertion	Fifth metatarsal tuberosity	First metatarsal and medial cuneiform	Dorsal base of fifth metatarsal
Eversion	Strong	Strong	Assists
Ankle action	Plantarflexion	Plantarflexion	Dorsiflexion

Anatomical Variations

Fibularis brevis can vary in the size and shape of its muscle belly and tendon. Accessory tendon slips may occur near the lateral ankle or fifth metatarsal.

An accessory muscle known as fibularis quartus may be present in the retromalleolar region and can alter the local anatomy of the fibular tendons.

Variations are important because additional muscle or tendon tissue can contribute to crowding within the relatively confined space behind the lateral malleolus.

Clinical Significance

Lateral Ankle Sprain

Fibularis brevis is functionally important during lateral ankle sprains. These injuries commonly occur when the foot undergoes excessive inversion.

The fibular muscles contract to oppose inversion and provide dynamic protection to the lateral ankle. Sudden or forceful inversion can therefore place substantial stress on the fibularis brevis muscle and tendon.

Fibularis Brevis Tendinopathy

Fibularis brevis tendinopathy may produce pain and tenderness along the posterolateral ankle and lateral foot.

Repetitive loading, chronic ankle instability, altered foot mechanics, or previous ankle trauma can increase stress on the tendon.

The tendon should be assessed together with fibularis longus because both travel through the retromalleolar region and disorders can affect either or both tendons.

Fibularis Brevis Tendon Tear

The fibularis brevis tendon may develop longitudinal split tears, particularly in the region behind the lateral malleolus.

The tendon occupies a constrained anatomical space and can be compressed between surrounding structures and the adjacent fibularis longus tendon.

MRI and ultrasound can help identify tendon thickening, splitting, discontinuity, and associated tenosynovitis.

Fibular Tendon Subluxation

Damage to the superior fibular retinaculum can allow the fibular tendons to subluxate or dislocate anteriorly over the lateral malleolus.

This may occur during forceful ankle movements or trauma and can produce snapping, pain, or instability along the posterolateral ankle.

Fibularis brevis and fibularis longus should both be evaluated when tendon instability is suspected.

Fifth Metatarsal Avulsion Fracture

Forceful inversion of the foot can transmit traction through the fibularis brevis tendon to its attachment on the fifth metatarsal tuberosity.

This mechanism can produce an avulsion fracture of the proximal fifth metatarsal.

The injury should be distinguished from other fractures of the proximal fifth metatarsal because fracture location, mechanism, healing characteristics, and management considerations differ.

Superficial Fibular Nerve Injury

Damage to the superficial fibular nerve can weaken both fibularis brevis and fibularis longus, reducing the strength of foot eversion.

Sensory changes may also occur over much of the dorsum of the foot because the distal branches of the nerve provide cutaneous innervation to this region.

The exact pattern of sensory loss depends on the level and extent of the lesion.

Chronic Ankle Instability

Fibularis brevis has an important role in patients with chronic lateral ankle instability. Recurrent inversion injuries can affect the lateral ligaments, fibular tendons, proprioception, and muscular control.

Weakness or delayed activation of the evertor muscles can reduce dynamic resistance to inversion.

The condition therefore involves both passive ligamentous restraints and active neuromuscular stabilization.

Surgical Reconstruction

The fibularis brevis tendon may be encountered or used in reconstructive procedures involving the lateral ankle and foot.

Its accessible distal tendon and strong fifth metatarsal attachment make it relevant to procedures involving tendon repair, stabilization, or reconstruction.

Knowledge of the superficial fibular nerve, sural nerve, retinacula, and neighboring fibularis longus tendon is important during surgical exposure.

Imaging

The fibularis brevis muscle and tendon can be evaluated with ultrasound and MRI. Ultrasound is particularly useful for dynamic assessment of tendon movement around the lateral malleolus.

MRI provides detailed visualization of the tendon, muscle belly, retinacula, neighboring fibularis longus tendon, and surrounding soft tissues.

Imaging may demonstrate tendinopathy, longitudinal tears, tenosynovitis, tendon instability, muscle injury, or anatomical variants.

Surface Anatomy

The fibularis brevis muscle belly lies deep to fibularis longus and is therefore less distinct on surface examination than the more superficial lateral compartment muscle.

Its tendon can be palpated posterior to the lateral malleolus and followed toward the prominent tuberosity at the base of the fifth metatarsal, particularly during resisted eversion.

The fifth metatarsal tuberosity provides a useful palpable landmark for identifying the distal attachment of fibularis brevis and understanding the muscle's mechanical role in eversion and lateral ankle stability.