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Fibularis longus muscle (peroneus longus muscle)

The fibularis longus, also known as the peroneus longus, is the most superficial muscle of the lateral compartment of the leg. It arises from the fibula and the surrounding fascia, then courses distally and posterior to the lateral malleolus. Its tendon passes across the sole of the foot to insert on the medial cuneiform and first metatarsal.

The fibularis longus plays a major role in ankle eversion, plantarflexion, and stabilization of the transverse arch of the foot. Clinically, it is important in lateral ankle injuries, peroneal tendon pathology, and chronic ankle instability.

Synonyms

  • Peroneus longus muscle

  • Long fibular muscle

  • Lateral leg eversion muscle

Origin and Insertion

  • Origin:

    • Head of fibula

    • Proximal two-thirds of the lateral surface of fibula

    • Adjacent intermuscular septa and deep fascia of leg

  • Course:

    • Fibers run downward in the lateral compartment

    • Tendon passes posterior to the lateral malleolus, through a groove on the cuboid bone, then across the sole of the foot

  • Insertion:

    • Base of the first metatarsal

    • Medial cuneiform

Nerve Supply

  • Superficial fibular (peroneal) nerve (L5–S2)

Arterial Supply

  • Fibular (peroneal) artery

  • Anterior tibial artery (contributions)

Venous Drainage

  • Fibular veins

  • Tributaries into anterior tibial and posterior tibial veins

Function

  • Eversion of the foot at the subtalar and transverse tarsal joints

  • Plantarflexion at the ankle joint (assists gastrocnemius–soleus complex)

  • Stabilization of the medial longitudinal and transverse arches of the foot

  • Provides lateral stability during gait and balance

MRI Appearance

T1-weighted images:

  • Normal muscle shows low-to-intermediate signal intensity

  • Surrounding subcutaneous and intramuscular fat appears bright

  • Fatty infiltration or chronic changes appear as higher signal

T2-weighted images:

  • Normal muscle shows low-to-intermediate signal intensity

  • Edema, strain, or tear appears as bright signal within the muscle or tendon

STIR (Short Tau Inversion Recovery):

  • Normal muscle shows low-to-intermediate signal

  • Acute pathology (strain, tear, myositis) shows bright hyperintensity

Proton Density Fat-Saturated (PD FS):

  • Normal muscle shows low-to-intermediate signal

  • Tendinopathy, tear, or inflammation appears as localized bright hyperintensity in muscle or tendon sheath

T1 Fat-Sat Post-Contrast:

  • Normal muscle shows mild uniform enhancement

  • Inflammatory lesions, infections, or tumors show focal, heterogeneous, or rim enhancement

  • Peroneal tendon sheath inflammation may show linear or circumferential enhancement

CT Appearance

Non-Contrast CT:

  • Muscle appears as homogeneous soft tissue density along lateral compartment of leg

  • Tendon seen posterior to lateral malleolus and along plantar foot course

  • Hematoma appears hyperdense acutely

  • Chronic fatty replacement appears hypodense

Post-Contrast CT:

  • Normal muscle enhances mildly and evenly

  • Pathology (inflammatory, neoplastic, or infectious) enhances heterogeneously

  • Abscess or necrotic lesions show rim enhancement with central low attenuation

MRI images

Fibularis longus (peroneus longus) muscle sag cross sectional anatomy 3T MRI radiology anatomy image-img-00000-00000

MRI images

Fibularis longus muscle anatomy 3t MRI image

MRI images

Fibularis longus muscle anatomy

CT image

Fibularis longus (peroneus longus) muscle CT axial image 0

CT image

Fibularis longus (peroneus longus) muscle CT axial image 1

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Fibularis longus (peroneus longus) muscle CT axial image 2

MRI image

Fibularis (peroneus) longus muscle axialcross sectional anatomy 3T MRI AI enhanced radiology image 2

MRI image

Fibularis (peroneus) longus muscle sagittal cross sectional anatomy 3T MRI AI enhanced radiology image 1

MRI image

Fibularis (peroneus) longus muscle sagittal cross sectional anatomy 3T MRI AI enhanced radiology image 2