Mutual position of the distal fibular physis and the tibiotalar joint space - radiological typology and clinical significance.

AIM The mutual position of the distal fibular physis compared to the tibiotalar joint space in the immature skeleton was investigated in X-ray studies. The clinical relevance of the recorded mutual position was evaluated for paediatric skeletal traumatology. MATERIALS AND METHODS 140 radiographs of immature ankle joints without skeletal injury were reviewed and the mutual position of the distal fibular physis and tibiotalar joint space was tested. We then reviewed a cohort of 30 children with skeletal injuries of both the distal tibial epiphysis and the distal fibula. The type of distal fibular injury was evaluated according to the mutual position of the distal fibular physis and the tibiotalar joint space. RESULTS We found that in about one-half of cases the distal fibular physis is located distally to the plane of the tibiotalar joint, which has not been considered in the literature. Thus, we defined three radiological types of immature ankle joint according to the vertical position of the distal fibular physis in relation to the tibiotalar joint space: type 1 - distal fibular physis is above the joint space; type 2 - distal fibular physis is on the same level as the joint space; type 3 - distal fibular physis is below the joint space. In the second cohort, we found that type 2 predisposes to physeal fibular injury and type 3 predisposes to metaphyseal fibular injury. All data obtained were statistically evaluated. CONCLUSIONS There are three radiological types of immature ankle joint. Type 1 is only an evolutionary type without clinical significance, type 2 predisposes to physeal and type 3 to metaphyseal fibular injury in combination with distal tibial physeal injury.