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Fibularis brevis tendon

The fibularis (peroneus) brevis tendon is the distal continuation of the fibularis brevis muscle, located in the lateral compartment of the leg. It runs behind the lateral malleolus within a common synovial sheath shared with the fibularis longus tendon, then courses forward along the lateral aspect of the calcaneus and inserts at the base of the fifth metatarsal.

It is an important stabilizer of the lateral ankle, playing a key role in eversion of the foot and protection against ankle inversion sprains. Due to its superficial location and course behind the lateral malleolus, the tendon is particularly vulnerable to tears, tendinitis, and subluxation.

Synonyms

  • Peroneus brevis tendon

  • Short fibular tendon

Origin, Course, and Insertion

  • Origin: Middle and lower two-thirds of the lateral surface of the fibula, deep to the fibularis longus

  • Course: Fibers converge into a tendon in the lower third of the leg, passing posterior to the lateral malleolus, within the fibular (peroneal) groove of the calcaneus, enclosed in a synovial sheath

  • Insertion: Tuberosity at the base of the fifth metatarsal on its lateral surface

Tendon Attachments

  • Runs with fibularis longus tendon in a common sheath behind the lateral malleolus

  • Stabilized by the superior and inferior peroneal retinacula

  • Inserts firmly into the base of the fifth metatarsal, occasionally sending slips to adjacent bones or fascia

Relations

  • Superiorly: Fibularis longus tendon (runs superficial and posterior)

  • Inferiorly: Fifth metatarsal base

  • Anteriorly: Lateral malleolus and fibular groove

  • Posteriorly: Calcaneus and peroneal retinacula

  • Laterally: Subcutaneous tissue of lateral ankle

  • Medially: Fibula and surrounding retinacular structures

Function

  • Eversion of foot: Primary function, working with fibularis longus

  • Ankle stabilization: Prevents excessive inversion, reducing risk of sprains

  • Load sharing: Assists lateral foot mechanics during walking and running

  • Dynamic support: Provides lateral ankle support, particularly in uneven terrain

Clinical Significance

  • Tears: Common in athletes and following inversion ankle injuries; longitudinal split tears frequently occur due to compression against the fibula

  • Tendinitis / tendinosis: Overuse or instability leads to pain and thickening of the tendon

  • Subluxation / dislocation: Can occur with retinaculum injury, causing snapping sensation around the lateral malleolus

  • Avulsion fractures: Tendon pull at its insertion may cause fracture of the base of the fifth metatarsal

  • Symptoms: Lateral ankle pain, swelling, instability, snapping sensation with movement

MRI Appearance

  • T1-weighted images:

    • Normal tendon: low signal (dark band) surrounded by intermediate signal muscle belly proximally

    • Surrounding fat: bright signal outlining tendon course

    • Tendinopathy: tendon thickening with intermediate signal intensity

    • Tears: focal hyperintense cleft within dark tendon structure

  • T2-weighted images:

    • Normal tendon: very dark signal, thinner band than on T1

    • Pathology: tears appear as linear or irregular bright signals within tendon substance

    • Peritendinous fluid or edema: bright hyperintensity around tendon sheath

    • Split tears: two parallel dark tendon bands with high-signal cleft between

  • STIR:

    • Normal tendon: dark signal

    • Inflammation or tear: hyperintense edema around or within tendon

    • Excellent for detecting peritendinitis and fluid in tendon sheath

  • Proton Density Fat-Saturated (PD FS):

    • Normal tendon: homogeneously dark

    • Partial tear: focal bright hyperintense signal, often crescent- or cleft-shaped

    • Complete tear: gap filled with fluid-like bright signal

    • Best for subtle split tears and degenerative changes

  • T1 Fat-Sat Post-Contrast:

    • Normal tendon: minimal enhancement

    • Pathology: tendinitis or sheath inflammation enhances brightly

    • Chronic tears: peripheral enhancement surrounding fluid-filled defect

CT Appearance

Non-Contrast CT:

  • Tendon: soft-tissue density structure posterior to lateral malleolus, difficult to isolate

  • Indirect signs: tendon thickening, associated calcifications, or avulsion fracture at fifth metatarsal base

  • Chronic tendinosis: may show irregular tendon margins

Post-Contrast CT (standard):

  • Tendon itself does not enhance significantly

  • Peritendinous inflammatory tissue or synovitis may show enhancement

  • Useful for excluding fractures and bone involvement in lateral ankle pain

MRI image

Fibularis brevis tendon axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI image

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

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MRI image

Fibularis brevis tendon axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00003

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