Bony Anatomy Overview
The ankle (talocrural) joint is a mortise formed by the distal tibia (tibial plafond and medial malleolus) and distal fibula (lateral malleolus) articulating with the talus. Inferior to the ankle, the hindfoot consists of the talus and calcaneus, the midfoot includes the navicular, cuboid, and three cuneiforms, and the forefoot consists of the metatarsals and phalanges. Stability of these joints is maintained by strong ligamentous structures, primarily the lateral ligament complex, deltoid ligament, distal tibiofibular syndesmosis, Lisfranc ligament, and spring ligament.
Ankle Ligament Introduction
Primary ligaments of the ankle include:
· Medial
• Deltoid ligament
• Calcaneonavicular (Spring) ligament
· Lateral
• Syndesmosis (AITFL, PITFL, TTFL, IOL)
• Anterior talofibular ligament (ATFL)
• Posterior talofibular ligament (PTFL)
• Calcaneofibular ligament (CFL)
• Lateral talocalcaneal ligament (LTCL)
Anterior Talofibular Ligament (ATFL)
The ATFL extends from the anteroinferior fibula to the talar neck. It is the weakest lateral ligament and the primary restraint to inversion when the ankle is plantarflexed, while also limiting anterior talar translation.
It is the most frequently injured ankle ligament, typically torn during inversion injuries. Rupture produces a positive anterior drawer test with excessive anterior talar translation. Stress radiographs showing >8 mm of translation suggest complete rupture. Recurrent ATFL injury may lead to chronic lateral ankle instability, impingement, and degenerative changes.
Calcaneofibular Ligament (CFL)
The CFL runs from the distal fibula to the lateral calcaneus, deep to the peroneal tendons. It crosses both the ankle and subtalar joints and resists inversion in neutral or dorsiflexed positions.
CFL injury usually occurs with more severe inversion trauma, often combined with ATFL rupture. A positive talar tilt test indicates combined injury. Increased talar tilt on stress radiographs confirms CFL insufficiency. Isolated CFL tears are uncommon but may contribute to subtalar instability.
Posterior Talofibular Ligament (PTFL)
The PTFL is the strongest lateral ligament, extending from the posterior fibula to the posterolateral talus. It stabilizes the ankle in dorsiflexion and prevents posterior talar displacement and excessive external rotation.
Isolated PTFL injury is rare and typically associated with high-energy trauma such as ankle dislocation or fracture-dislocation. No reliable isolated clinical test exists; MRI may be used in severe cases.
Deltoid (Medial Collateral) Ligament
The deltoid ligament complex connects the medial malleolus to the talus, calcaneus, and navicular.
It consists of:
• Superficial layer (tibiocalcaneal, tibionavicular, superficial tibiotalar) — crosses ankle and subtalar joints
• Deep layer (anterior tibiotalar) — crosses the ankle only and is the primary stabilizer preventing lateral talar shift
The deltoid ligament resists valgus tilt, hindfoot eversion, and external rotation. Isolated deltoid sprains are uncommon and usually occur with ankle fractures or syndesmotic injury.
Clinically, patients present with medial ankle pain and swelling. Eversion stress tests the superficial layer, while external rotation stress evaluates the deep layer. Medial clear space >4–5 mm on mortise radiographs indicates deltoid incompetence and often necessitates surgical stabilization.
Distal Tibiofibular Syndesmosis
The syndesmosis consists of the AITFL, PITFL, interosseous ligament, and transverse ligament, maintaining ankle mortise integrity.
Injury (high ankle sprain) results from external rotation or hyperdorsiflexion. Patients present with pain above the ankle joint. Clinical tests include the external rotation stress test and the squeeze test.
Radiographic findings include increased tibiofibular clear space (>5 mm) and decreased tibiofibular overlap. Unstable injuries frequently require surgical fixation.
Lisfranc (Tarsometatarsal) Ligament
The Lisfranc ligament connects the medial cuneiform to the base of the second metatarsal and is the primary stabilizer of the midfoot.
Injury occurs with axial load or twisting on a plantarflexed foot, producing midfoot pain, swelling, plantar ecchymosis, and impaired weight bearing.
Weight-bearing radiographs reveal diastasis between the 1st and 2nd metatarsals, malalignment of the 2nd metatarsal with the medial cuneiform, or the fleck sign. Unstable injuries require surgical fixation to prevent chronic deformity and arthritis.
The spring ligament supports the talar head and medial longitudinal arch, extending from the sustentaculum tali to the navicular. The superomedial component is the primary stabilizer.
Failure of this ligament, commonly associated with posterior tibial tendon dysfunction, results in adult-acquired flatfoot deformity with arch collapse, hindfoot valgus, and forefoot abduction. MRI is the preferred imaging modality. Advanced deformity often requires surgical reconstruction.
Bifurcate Ligament (Chopart Ligament)
The bifurcate ligament stabilizes the transverse tarsal (Chopart) joint and limits midfoot inversion. It originates from the anterior calcaneus and divides into calcaneonavicular and calcaneocuboid bands. Injury presents as persistent lateral midfoot pain and is frequently underdiagnosed. CT detects avulsion fractures; MRI evaluates ligament integrity.
Clinical Correlation
Ligament integrity is essential for normal biomechanics of the foot and ankle. Disruption of the lateral ankle ligaments results in chronic ankle instability with recurrent sprains and degenerative changes.
Failure of medial stabilizers, particularly the spring ligament with posterior tibial tendon dysfunction, leads to adult-acquired flatfoot deformity.
Midfoot ligament injury, especially of the Lisfranc complex, causes tarsometatarsal instability, deformity, and early arthritis if untreated.