Posterior Plating Through a Single Posterolateral Approach for a Comminuted Thurston-Holland Fragment in a Pediatric Triplane Ankle Fracture.

We present the case of a 12-year-old boy who sustained a three-part triplane fracture of the left distal tibia following a torsional fall, with a small, comminuted posterior Thurston-Holland fragment. Triplane fractures are transitional injuries unique to mid-adolescence. While displaced fractures are conventionally managed through an anterior approach with indirect reduction of the posterior fragment, this technique relies on the posterior fragment being a single, congruent piece. In the present case, comminution of the posterior fragment precluded reliable indirect reduction, prompting a posterolateral surgical approach to achieve anatomical reduction under direct visualization. The patient presented with pain, edema, deformity, and inability to ambulate, with the overlying skin tense and blanched over the deformity. Computed tomography confirmed a three-part triplane fracture comprising an anterolateral (Tillaux) fragment, a medial epiphyseal fragment, and a comminuted posterior metaphyseal fragment. The patient underwent open reduction and internal fixation performed entirely through a single posterolateral approach, with Kirschner-wire fixation of the posterior and Tillaux fragments and percutaneous screw fixation of the medial fragment. At final follow-up, the patient achieved an American Orthopaedic Foot and Ankle Society (AOFAS) Ankle-Hindfoot score of 99 out of 100 points, reflecting an excellent functional outcome. This case supports extrapolating posterior fixation principles well established in adult trimalleolar ankle fracture surgery to the pediatric transitional ankle fracture population and suggests that fragment morphology, rather than fracture classification alone, should guide the choice of surgical approach.