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Posterior intermalleolar ligament

The posterior intermalleolar ligament (PIML) is a variable but frequently present ligament in the ankle joint. It extends between the posterior aspect of the medial malleolus (tibia) and the posterior aspect of the lateral malleolus (fibula). The ligament runs obliquely across the posterior ankle joint, posterior to the talus.

The PIML is not always present in all individuals, but when it exists, it plays a role in posterior ankle stability. It has gained clinical importance as a contributor to posterior ankle impingement syndrome, especially in athletes and ballet dancers, due to its position behind the talus and its tendency to become thickened or fibrotic.

Synonyms

  • Posterior transverse intermalleolar ligament

  • Intermalleolar ligament of the ankle

Origin, Course, and Insertion

  • Origin: Posterior margin of the medial malleolus (tibia)

  • Course: Runs obliquely laterally and slightly posteriorly across the posterior ankle joint, posterior to the talus

  • Insertion: Posterior margin of the lateral malleolus (fibula)

Relations

  • Anteriorly: Posterior aspect of the talus

  • Posteriorly: Subcutaneous tissue, Achilles tendon region

  • Medially: Medial malleolus and posterior tibiotalar structures

  • Laterally: Lateral malleolus and posterior talofibular ligament

  • Superiorly: Distal tibia and fibula

  • Inferiorly: Posterior joint capsule of the ankle

Function

  • Stabilization: Helps stabilize the posterior aspect of the ankle joint

  • Posterior support: Acts as a secondary stabilizer to prevent excessive posterior talar translation

  • Clinical role: May contribute to posterior ankle impingement when thickened or hypertrophied

  • Protective effect: May reinforce the posterior capsule of the ankle joint

Clinical Significance

  • Anatomical variation: Present in up to 70% of individuals, absent in others

  • Posterior ankle impingement: Thickened or fibrotic PIML may be compressed between tibia, fibula, and talus during plantarflexion

  • Sports relevance: Common in ballet dancers, football players, and athletes requiring repeated plantarflexion

  • Diagnostic imaging: Can be mistaken for a loose body, hypertrophic synovium, or posterior capsule fold

  • Surgical importance: Recognition is important during posterior ankle arthroscopy and impingement surgery

MRI Appearance

  • T1-weighted images:

    • Normal PIML: low-signal (dark) band-like structure posterior to the talus, connecting tibia and fibula

    • Thickened ligament: appears bulkier but still dark; may show intermediate signal in degeneration

    • Fat planes around ligament: bright, aiding delineation

  • T2-weighted images:

    • Normal: dark linear structure posterior to talus

    • Pathology: bright hyperintense signal in ligament substance indicates edema, strain, or partial tear

    • Posterior impingement: hypertrophied ligament may show high T2 signal and thickening

  • STIR:

    • Normal ligament: low signal

    • Abnormal ligament: bright hyperintensity in impingement, edema, or partial disruption

    • Periligamentous edema well highlighted

  • Proton Density Fat-Saturated (PD FS):

    • Normal: uniform low signal band

    • Pathology: bright focal or diffuse signals indicate sprain, mucoid degeneration, or entrapment changes

    • Best sequence to detect subtle ligament thickening in posterior impingement

  • T1 Fat-Sat Post-Contrast:

    • Normal: minimal or no enhancement

    • Pathology: enhancing hypertrophic or fibrotic PIML suggests synovial inflammation or chronic impingement changes

CT Appearance

Non-Contrast CT:

  • Ligament itself not well visualized due to soft tissue density

  • May appear as a thin soft tissue band posterior to talus in high-resolution CT

  • Chronic thickening may present as posterior joint space narrowing or subtle soft tissue density

Post-Contrast CT (standard):

  • Ligament not directly enhanced

  • Surrounding synovial changes or fibrosis may show indirect enhancement

  • Useful in ruling out posterior loose bodies or bony impingement lesions

MRI images

Posterior intermalleolar ligament axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI images

Posterior intermalleolar ligament coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000