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Lateral malleolus

The lateral malleolus is the distal end of the fibula that projects laterally at the ankle joint. It plays a critical role in ankle stability by forming the lateral wall of the ankle mortise and providing attachment sites for key stabilizing ligaments. It is commonly injured in ankle fractures and ligamentous injuries, making it highly important in trauma imaging.

Joints

  • Forms part of the talocrural (ankle) joint by articulating with the lateral aspect of the talus

  • Contributes to the distal tibiofibular syndesmosis, stabilizing the ankle mortise

Ligament Attachments

  • Anterior talofibular ligament (ATFL): From anterior margin of lateral malleolus to talus

  • Calcaneofibular ligament (CFL): Runs from tip of malleolus to calcaneus

  • Posterior talofibular ligament (PTFL): From posterior aspect of malleolus to talus

  • Anterior inferior tibiofibular ligament (AITFL): Anchors tibia to fibula anteriorly

  • Posterior inferior tibiofibular ligament (PITFL): Anchors tibia to fibula posteriorly

Tendon and Muscle Relations

  • Posterior to malleolus: Peroneus longus and brevis tendons pass in a fibrous tunnel behind lateral malleolus

  • Anterior to malleolus: Tendons of extensor digitorum longus and peroneus tertius cross

  • Superior retinaculum: Peroneal retinaculum stabilizes peroneal tendons posterior to lateral malleolus

Nerve Supply

  • Superficial peroneal nerve: Supplies overlying skin

  • Deep peroneal nerve and sural nerve: Contribute to ankle joint innervation

Arterial Supply

  • Peroneal artery: Primary supply via branches to distal fibula

  • Anterior tibial artery: Contributes at ankle mortise

  • Posterior tibial artery: Minor contributions

Venous Drainage

  • Drains into peroneal, anterior tibial, and posterior tibial veins

Function

  • Provides lateral support to ankle mortise

  • Acts as an anchor for lateral ankle ligaments

  • Forms pulley system for peroneal tendons

  • Essential in stabilizing ankle during inversion/eversion

Clinical Significance

  • Fractures: Very common in ankle trauma; Weber classification based on level of fibular fracture

  • Syndesmotic injuries: Involve tibiofibular ligaments and destabilize ankle mortise

  • Ligament injuries: ATFL most commonly torn in inversion injuries

  • Peroneal tendon pathology: Dislocation or tenosynovitis often occurs behind malleolus

  • Imaging role: MRI/CT crucial for assessing fractures, ligament injuries, and peroneal tendon stability

MRI Appearance

  • T1-weighted images:

    • Cortical bone: uniformly low signal (dark)

    • Bone marrow: intermediate-to-high signal depending on fat content

    • Fractures: linear low-signal lines within malleolus

    • Bone marrow edema: low-to-intermediate

  • T2-weighted images:

    • Cortical bone: dark low signal

    • Bone marrow: intermediate-to-high signal depending on fat

    • Edema or stress fracture: bright hyperintense marrow changes

    • Associated ligament injury: hyperintense signal along ATFL, CFL, or PTFL

  • STIR:

    • Cortical bone: dark

    • Bone marrow edema, occult fractures: bright hyperintense

    • Highlights soft-tissue swelling and peroneal tendon sheath fluid

  • Proton Density Fat-Saturated (PD FS):

    • Cortical bone: sharply defined dark rim

    • Normal marrow: homogeneous dark-to-intermediate signal

    • Fractures: bright signal lines and marrow edema

    • Excellent for peroneal tendon pathology and ligament injuries

MRI Arthrogram Appearance

  • Contrast fills ankle joint and syndesmosis

  • Identifies small intra-articular fractures or osteochondral fragments

  • Outlines ATFL and CFL tears with contrast extravasation

  • Useful in chronic ankle instability assessment

CT Appearance

Non-Contrast CT:

  • Best modality for detecting fractures and cortical bone detail

  • Cortical bone: high-density sharply defined rim

  • Marrow: low density, fractures visible as clear cortical breaks or lucent lines

  • Assesses fracture displacement, syndesmotic widening, and intra-articular extension

CT Arthrogram Appearance:

  • Contrast highlights the ankle joint capsule and syndesmosis

  • Reveals osteochondral fragments and subtle articular defects

  • Detects contrast leakage into peroneal tendon sheath in complex ligament tears

CT VRT 3D image

Lateral malleolus ct 3d

MRI image

Lateral malleolus MRI axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI image

Lateral malleolus MRI coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI image

Lateral malleolus MRI sagittal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

CT image

Lateral malleolus ct axial