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Posterior inferior tibiofibular ligament

The posterior inferior tibiofibular ligament (PITFL) is a strong fibrous band that forms the posterior component of the distal tibiofibular syndesmosis. It extends from the posterior margin of the distal tibia to the posterior aspect of the distal fibula, helping to stabilize the ankle mortise.

It is the thickest and strongest ligament of the syndesmosis complex, and functions synergistically with the anterior inferior tibiofibular ligament (AITFL), interosseous ligament, and transverse tibiofibular ligament. The PITFL plays a crucial role in preventing posterior and external rotation displacement of the fibula and is essential for ankle stability.

Synonyms

  • Posterior tibiofibular ligament

  • Posterior distal tibiofibular ligament

Origin, Course, and Insertion

  • Origin: Posterior margin of the distal tibia, just proximal to the ankle joint

  • Course: Runs obliquely downward and laterally across the posterior ankle syndesmosis

  • Insertion: Posterior surface of the distal fibula, blending partially with the transverse tibiofibular ligament

Relations

  • Anteriorly: Interosseous ligament and anterior inferior tibiofibular ligament

  • Posteriorly: Flexor hallucis longus tendon and posterior ankle capsule

  • Superiorly: Posterior tibial plafond

  • Inferiorly: Posterior aspect of the ankle mortise and talus

Function

  • Ankle stability: Primary stabilizer of the distal tibiofibular syndesmosis

  • Posterior restraint: Prevents posterior and external rotation displacement of the fibula

  • Mortise support: Maintains congruency of tibiofibular articulation for proper ankle joint mechanics

  • Load distribution: Resists separation of tibia and fibula under weight-bearing

Clinical Significance

  • Syndesmotic injuries: PITFL injuries are seen in high ankle sprains, especially with external rotation and dorsiflexion trauma

  • Avulsion fractures: May pull off a fragment of the tibia (posterior malleolus) or fibula

  • Chronic instability: Failure to heal can lead to ankle instability and degenerative arthritis

  • Surgical relevance: PITFL reconstruction or repair is sometimes necessary in severe syndesmotic injuries

  • Imaging importance: Evaluation on MRI is critical in grading ankle syndesmosis sprains

MRI Appearance

  • T1-weighted images:

    • Normal PITFL: low signal (dark, cord-like band) connecting distal tibia and fibula

    • Tear: focal or complete discontinuity, with intermediate-to-bright signal gap

    • Surrounding fat: bright signal, helping outline the ligament

  • T2-weighted images:

    • Normal: low signal, thin band posterior to the tibiofibular joint

    • Tear/strain: bright hyperintense signal within or around ligament

    • Partial tear: increased thickness, irregular contour, and hyperintensity

    • Complete tear: absent or fully discontinuous low-signal band

  • STIR:

    • Normal ligament: dark, sharply defined

    • Injury: bright hyperintensity indicating edema, fluid, or hemorrhage

  • Proton Density Fat-Saturated (PD FS):

    • Normal: thin, compact dark band

    • Pathology: bright linear or diffuse signal, edema in surrounding soft tissue

    • Best for detecting partial tears and subtle sprain

  • T1 Fat-Sat Post-Contrast:

    • Normal: minimal or no enhancement

    • Pathology: enhancement around torn fibers due to inflammation or synovitis

CT Appearance

Non-Contrast CT:

  • PITFL itself poorly visualized as a soft tissue band

  • Indirect signs: widening of syndesmosis, posterior malleolar avulsion fractures, malalignment

  • Chronic injury: calcification or ossification along ligamentous course

Post-Contrast CT (standard):

  • Ligament remains poorly visualized

  • Adjacent inflammatory or post-traumatic soft-tissue enhancement may be seen

MRI image

Posterior inferior tibiofibular ligament Axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI image

Posterior inferior tibiofibular ligament coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001

CT image

Posterior inferior tibiofibular ligament ct image