![]() 19, 20 Thus, clinical exam findings may be used to distinguish a nondisplaced avulsion fracture from an ossification center. The medial os subtibiale is more prevalent than the lateral os subfibulare. The distal fibula frequently has a secondary center of ossification which can mimic an avulsion fracture on radiograph. The distal fibula physis becomes undulating during childhood, which does provide it with additional stability 18. Thus, the same injury mechanism which may result in an ankle sprain in adults can present with physeal or avulsion fractures in children. Ligamentous structures in children are quite robust, whereas the physis is biomechanically vulnerable to shear and rotational forces. The distal fibula is contained in a groove on the lateral distal tibia with significant ligamentous constraint with the anterior and posterior tibiofibular and calcaneofibular ligaments. Abundant blood supply is provided to the distal tibial physis, so post-traumatic avascular necrosis of the plafond is very rare. Physeal arrest is generally not a concern for triplane and Tillaux fractures, since the physis is already closing in these fracture patterns. This pattern of closure explains the specific tibial physeal fracture patterns seen in adolescent triplane and Tillaux fractures. In contrast to other physes, tibial physeal closure occurs slowly and eccentrically, beginning around Poland’s hump, and then anteromedially, posterolaterally, and finally anterolaterally. Distal tibial and fibular physeal closure occurs around 12 to 17 years in females and 15 to 20 in males 17, 18. The distal tibial ossification center appears around 6 months of age and the distal fibula around 1 to 3 years of age. Thus, injury to the physis at a young age can result in significant leg length discrepancy. Distal tibial growth occurs proportionately to the proximal tibia in young patients, but in adolescents the proximal tibia growth becomes more rapid and distal tibial growth tapers off 16. The distal tibial physis provides 40% of the growth of the tibia and 17% of lower extremity growth, with 3–4 mm of growth per year in childhood. Fractures which cross the physis into the epiphysis (Salter Harris III and IV types), however, may damage the reserve zone and thus are at higher risk of causing physeal growth disturbance. For most fractures, this in turns preserves the reserve zone, which is located on the epiphyseal side of the fracture and contains the progenitor cells for physeal growth 14, 15. Fracture typically occurs through the hypertrophic zone, which has the largest cells and less extracellular matrix than the other zones. The physis contains four zones, from the epiphysis to the metaphysis with decreasing mechanical strength due to decreasing matrix-cell ratio: reserve zone, proliferative zone, hypertrophic zone and the provisional calcification zone. Of all physeal injuries, fractures of the distal tibial physis have among the highest rates of complications, including premature physeal arrest, bar formation, angular deformity, and articular incongruity 12, 13.
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