Case of the Week

Editor: Dr Danielle Coleman

This is a dislocation of the ankle joint. Due to the intrinsic stability of the tibio-talar joint dislocation of the ankle joint is rarely seen without a fracture. Dislocation is usually caused by high energy trauma e.g. road traffic accident or jumping sports, commonly involving plantar flexion combined with either an inversion/eversion force upon the foot. Ankle dislocation is commonest in adolescents and young males. Furthermore, individuals with a prior history of ankle sprain or dislocation, malleolar hypoplasia, peroneal muscle weakness and connective tissue disorders that convey ligamentous laxity e.g. Ehlers-Danlos syndrome are at an increased risk.

Anterior, posterior, lateral and superior dislocations can present to the E.D. dependant on the mechanism of injury. A posterior dislocation is the commonest – the force drives the foot backwards causing the talus to move in a posterior direction in relation to the distal tibia. A concomitant fracture of the lateral malleolus or disruption of the tibio-fibular syndesmosis occurs. Anterior dislocations of the talus are associated with loss of the dorsalis pedis pulse due to displacement and compression of the talus.

It is essential to reduce the dislocation in the E.D. to avoid tenting of the skin over the anterior tibia (evident in the picture above). Neurovascular compromise is a foremost concern as avascular necrosis of the talus, sensory damage and lower extremity ischaemia may ensue. Various closed reduction manoeuvres exist and depend on the type of dislocation. The main principles include conscious sedation, then placing one hand on the heel and another on the dorsum of the foot. An assistant then applies a hand to the distal tibia and axial traction is applied. Further manoeuvres apply an oppositional force to the direction of injury. The joint is immobilised in 90o flexion with opening of the cast distally to allow for repeated neurovascular assessments. Orthopaedic referral is required for fracture management and for open fractures.

Closed reduction becomes difficult if osseous fragments, ruptured tendons and ligaments disrupt the anatomical space and surgical involvement should be prompted if failed reduction after 2-3 attempts, increased skin tenting and need for amputation occurs. Vigilance is required as, during closed reduction, the skin can rupture converting the ankle into a open injury thus requiring tetanus and antibiotic prophylaxis and surgical debridement. Evidence of subtalar dislocation (either clinically or radiographically) is a contraindication to reduction as 20% of cases are irreducible by closed methods. Optimal radiographic studies include pre- and post-reduction films (AP, lateral). This should not delay the time to reduction in a neurovascularly compromised joint. CT imaging also plays a role in defining intricate anatomical disruptions.