We studied the cases of nine adolescent patients with a Salter-Harris Type-III fracture of the lateral portion of the distal tibial epiphysis (sometimes called the juvenile Tillaux fracture) and eight patients with a triplane fracture of the distal tibial epiphysis. The mechanism of both injuries was postulated to be external rotation of the foot on the leg. There were both two-fragment and three-fragment triplane fractures in the series. The three-fragment triplane fractures occurred in younger patients, and surgical treatment was more frequently administered. The pattern of closure of the distal tibial growth plate in the adolescent strongly influenced the type of fracture.