Medial Subtalar Dislocation: A Comprehensive Clinical Case & Imaging Guide
Key Takeaway
Medial subtalar dislocation is diagnosed via detailed clinical examination revealing characteristic hindfoot valgus, lateral calcaneal displacement, and a palpable medial talar head. Plain radiographs confirm complete talocalcaneal and talonavicular disarticulation with an intact tibiotalar joint. CT scans are crucial post-reduction to detect occult fractures or incarcerated fragments and ensure concentric reduction.
A 32-year-old male presents to the ED after a high-energy motor vehicle collision. He has a gross deformity of the left hindfoot. You are presented with the patient's initial plain film. Describe your findings and identify the likely injury.
Candidate: The radiograph shows a complete dislocation of the subtalar joint. There is loss of articulation between the talus and calcaneus, as well as the talus and the navicular. The talus remains within the ankle mortise. The foot is displaced medially relative to the talus. This is a classic medial subtalar dislocation.
Failing to emphasize that the tibiotalar joint is preserved. A poor candidate might call it a "pantalar dislocation" or simply "ankle dislocation," missing the critical distinction that the talus remains in the mortise, which classifies this as a peritalar/subtalar injury.
Systematically describe the loss of the subtalar and talonavicular joints while confirming the integrity of the tibiotalar articulation. Explicitly identify the injury as a "Medial Subtalar Dislocation," note the high-energy mechanism, and immediately state the management priority: "This is an orthopaedic emergency requiring urgent closed reduction to prevent skin necrosis from the prominent, dorsolaterally displaced talar head."
You have successfully reduced the dislocation in the ED. The patient’s neurovascular status is intact, and the skin is stable. What are the next steps in your management, and why?
Candidate: I would place the patient in a well-padded backslab splint with the knee flexed. Crucially, I would order a CT scan of the foot and ankle to rule out any associated osteochondral shear fractures or occult fractures of the talar process or sustentaculum tali, which can block reduction or lead to post-traumatic arthritis.
Stating that the patient can be discharged or managed with plain radiographs only. Failing to recognize the high incidence of occult intra-articular injuries on CT that significantly alter management/prognosis is a major red flag.
"Management follows a three-pillar approach: 1) Stabilization in a splint with the knee flexed to 90 degrees to negate the gastrocnemius deforming force. 2) Urgent post-reduction CT scan to identify intra-articular fragments (e.g., lateral process fractures) that dictate the need for ORIF versus conservative management. 3) Longitudinal monitoring for neurovascular integrity and skin viability, as the energy required for this injury often leads to long-term sequelae including stiffness and post-traumatic arthrosis."
What are the potential "blocks" to closed reduction if you were to attempt this, and how would you manage an irreducible dislocation?
Candidate: The most common blocks to reduction in a medial dislocation include the extensor digitorum brevis muscle belly, the extensor retinaculum, or the talonavicular joint capsule. If it remains irreducible after two attempts under adequate sedation, I would take the patient to the operating room for an open reduction, typically through an anterolateral approach to remove the obstructing soft tissue.
Attempting too many closed reductions in the ED, which increases soft tissue damage, or failing to recognize that "buttonholing" is the primary mechanism of irreducibility.
Define the anatomical blocks clearly (EDB, retinaculum, joint capsule). Emphasize that persistence of the deformity despite adequate analgesia/relaxation mandates an urgent open reduction. Mention the anterolateral approach as the standard for identifying and freeing the entrapped structures, and verify that the reduction must be confirmed as concentric under direct visualization or fluoroscopy.
