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Fibularis brevis muscle

The fibularis brevis muscle is a short, fusiform muscle of the lateral compartment of the leg. It lies deep to the fibularis longus muscle and functions primarily as an everter of the foot and a weak plantarflexor of the ankle.

The fibularis brevis has a long tendon that courses posterior to the lateral malleolus, sharing a synovial sheath with the fibularis longus tendon, before inserting at the base of the fifth metatarsal. It plays a key role in maintaining lateral ankle stability, and its tendon is frequently involved in ankle sprains, peroneal tendon subluxation, and tears.

Synonyms

  • Peroneus brevis muscle

  • Short fibular muscle

Origin, Course, and Insertion

  • Origin: Distal two-thirds of the lateral surface of the fibula and intermuscular septa

  • Course: Fibers descend vertically, forming a tendon that passes posterior to the lateral malleolus within the common peroneal tendon sheath, anterior to the fibularis longus tendon

  • Insertion: Tuberosity at the base of the fifth metatarsal (lateral aspect)

Tendon Attachments

  • Runs in the retro-malleolar groove of the fibula, posterior to the lateral malleolus

  • Secured by the superior and inferior peroneal retinacula

  • Inserts into the styloid process of the fifth metatarsal, with occasional slips to adjacent metatarsals

Relations

  • Superficial: Fibularis longus muscle

  • Deep: Fibula and interosseous membrane

  • Medial: Fibularis tertius and extensor digitorum longus (anteriorly)

  • Posterior: Peroneal retinacula and calcaneofibular ligament

Nerve Supply

  • Superficial fibular (peroneal) nerve (L5–S1)

Arterial Supply

  • Fibular (peroneal) artery branches

  • Contributions from the anterior tibial artery

Venous Drainage

  • Fibular veins and tributaries of the anterior tibial vein, draining into the popliteal vein

Function

  • Eversion of the foot: Primary function, balancing medial pull of tibialis anterior and posterior

  • Plantarflexion of ankle: Weak but assists gastrocnemius and soleus

  • Lateral stability: Prevents inversion injuries by stabilizing lateral ankle

  • Dynamic support: Maintains balance during walking and running

Clinical Significance

  • Tendon tears: Fibularis brevis is the most commonly torn peroneal tendon due to repetitive inversion injuries

  • Subluxation/dislocation: Can occur if the superior peroneal retinaculum is ruptured

  • Tendinopathy: Seen in chronic ankle instability or overuse

  • Avulsion fracture: Insertion at the fifth metatarsal base may pull off (Dancer’s fracture)

  • Surgical importance: Tendon repair or debridement critical in chronic tears

MRI Appearance

  • T1-weighted images:

    • Normal muscle: intermediate signal intensity

    • Tendon: low signal (dark band) coursing posterior to lateral malleolus

    • Tears: focal hyperintense signals or discontinuity within tendon

    • Fat planes around tendon appear bright

  • T2-weighted images:

    • Normal muscle: intermediate to dark, slightly darker than T1

    • Normal tendon: very low signal (black)

    • Tendinopathy: tendon thickening with intermediate-to-bright signal

    • Partial tear: focal bright intratendinous signal; complete tear: fluid-filled gap

  • STIR (Short Tau Inversion Recovery):

    • Normal muscle: intermediate to dark

    • Pathology: bright hyperintense signal indicating tendon edema, sheath fluid, or peritendinitis

  • Proton Density Fat-Saturated (PD FS):

    • Normal muscle: intermediate to dark

    • Normal tendon: dark, uniform low signal

    • Tendon tears: bright focal signals within tendon or sheath

    • Excellent for detecting subtle longitudinal splits and peroneal tendon dislocation

  • T1 Fat-Sat Post-Contrast:

    • Normal tendon: minimal enhancement

    • Tenosynovitis: enhances along tendon sheath

    • Tear edges: may enhance due to granulation tissue

CT Appearance

Non-Contrast CT:

  • Muscle belly: soft-tissue density, not well separated from fibularis longus

  • Tendon: dense band posterior to lateral malleolus, best seen in cross-section

  • Pathology: tendon thickening, calcifications, or fifth metatarsal avulsion fractures

Post-Contrast CT (standard):

  • Muscle enhances homogeneously

  • Inflamed tendon sheath may show contrast enhancement

  • Useful for evaluating peroneal tendon sheath pathology and osseous injuries

MRI image

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Fibularis brevis muscle MRI sag cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

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Fibularis brevis muscle MRI sag cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001

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Fibularis brevis muscle MRI sag cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00002

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