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Accessory anterior inferior tibiofibular (Bassett’s) ligament

The accessory anterior inferior tibiofibular ligament (AITFL), also known as Bassett’s ligament, is a distinct anatomical variant found in a significant portion of the population. It is a thin band of fibrous tissue that runs parallel and just inferior to the anterior inferior tibiofibular ligament at the distal tibiofibular syndesmosis.

Although not always present, when prominent, Bassett’s ligament can play a role in anterolateral ankle impingement, particularly after ankle sprains. Because of its location within the ankle mortise, it can become entrapped between the talus and distal tibia during dorsiflexion, leading to chronic pain and restricted ankle motion.

Synonyms

  • Accessory anterior inferior tibiofibular ligament

  • Distal fascicle of the AITFL

  • Bassett’s ligament

Origin, Course, and Insertion

  • Origin: Anterior distal tibia, just inferior to the main anterior inferior tibiofibular ligament

  • Course: Runs obliquely downward and laterally, lying close to the anterior ankle joint capsule

  • Insertion: Anterior aspect of the lateral malleolus (fibula), adjacent to the AITFL attachment

Relations

  • Superiorly: Anterior inferior tibiofibular ligament (AITFL)

  • Inferiorly: Ankle joint capsule and talar dome

  • Anteriorly: Extensor tendons crossing the ankle (extensor hallucis longus, tibialis anterior)

  • Posteriorly: Talus at the talocrural joint, where impingement may occur

Function

  • Variant stabilizer: May act as a minor stabilizing structure for the distal tibiofibular syndesmosis

  • Clinical impact: Its functional role is limited, but when thickened or hypertrophic, it may contribute to ankle impingement

Clinical Significance

  • Ankle impingement: Hypertrophy or scarring of Bassett’s ligament can become entrapped between the talus and tibia, causing anterolateral ankle pain

  • Post-trauma: Often implicated after ankle sprains or syndesmotic injuries

  • Symptoms: Chronic ankle pain, stiffness, or painful clicking during dorsiflexion

  • Surgical relevance: Can be resected during arthroscopy in cases of impingement

  • Imaging importance: Recognizing it prevents misinterpretation as scar tissue, meniscoid lesions, or abnormal AITFL thickening

MRI Appearance

  • T1-weighted images:

    • Ligament appears as a thin, low-signal (dark) band beneath the anterior inferior tibiofibular ligament

    • Surrounded by intermediate-signal fat planes in the ankle mortise

    • Difficult to identify unless hypertrophic or inflamed

  • T2-weighted images:

    • Normal ligament remains dark but may appear slightly darker than on T1

    • Pathology: bright hyperintense thickening in cases of edema, hypertrophy, or scarring

    • Adjacent bone marrow edema in the talus or tibia may be seen with impingement

  • STIR:

    • Normal ligament: low signal

    • Pathology: hyperintense signal consistent with edema, fibrosis, or scarring

  • Proton Density Fat-Saturated (PD FS):

    • Normal: uniformly dark

    • Pathology: bright, thickened band between tibia and talus indicating inflammation or hypertrophy

    • Particularly useful for detecting subtle impingement syndromes

  • T1 Fat-Sat Post-Contrast:

    • Normal: minimal or no enhancement

    • Inflamed or fibrotic ligament may enhance

    • Surrounding synovial proliferation can also show enhancement

CT Appearance

Non-Contrast CT:

  • Ligament rarely visualized directly due to small size

  • Indirect signs: irregularity, sclerosis, or osteophytes at anterior tibial plafond or talar dome from chronic impingement

Post-Contrast CT (standard):

  • Limited role for direct visualization

  • May demonstrate surrounding synovial thickening or subtle impingement-related changes

MRI image

Accessory anterior inferior tibiofibular (Bassett’s) ligament AXIAL cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001

MRI image

Accessory anterior inferior tibiofibular (Bassett’s) ligament coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI image

Accessory anterior inferior tibiofibular (Bassett’s) ligament SAG cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001