Only four cases of triplane distal radius fracture have been described in the literature. We report the first that has been treated with open reduction and internal fixation. A 15-year-old boy sustained a triplane fracture of the distal radius. After an unsuccessful attempt at closed reduction, open reduction and internal fixation were performed. Six months after injury, the patient is asymptomatic, but radiographs show a partial growth arrest. The goal of treatment is to achieve anatomic reduction of the articular surface. In this case interposed periosteum prevented anatomic reduction, requiring open reduction and internal fixation. Because of the patient’s advanced age the partial physeal arrest should advance to complete arrest before length impairment or occurrence of angular deformity.