Postnatal epiphyseal development: the distal tibia and fibula.

At birth, the distal tibial physis is a transverse structure. However, as the tibia enlarges diametrically and the epiphyseal ossification center matures, the physis becomes increasingly undulated, with peripheral lappet formation. The anteromedial area is the first to develop undulation (Poland's hump). This should not be misinterpreted as an injury or premature epiphyseodesis subsequent to trauma. The tibial secondary ossification center forms within the central epiphysis. The medial margin is irregular and may have peripheral foci of ossification. Between the ages of 7 and 8 years, this secondary center extends into the medial malleolus, reaching the distal tip during adolescence. The malleolar tip may develop accessory ossification. Physiologic epiphyseodesis begins over the medial malleolus and then extends laterally, a pattern of closure that affects fracture patterns (e.g., the fracture of Tillaux). The distal fibular physis also begins as a transverse structure that becomes undulated and has extensive peripheral lappet formation. This physis usually becomes level with the articular surface of the distal tibia after the first year. Enchondromalike extensions of the physis into the metaphysis are common. Accessory ossification may develop at the distal end.