We tried to evaluate the role of lateral malleolus in development and biomechanics of ankle in growing children through the clinical long-term follow-up study for the nine cases of fibular pseudoarthrosis and also the nine children with epiphyseal injury of distal tibial eplphysis, and followed them for more than 10 years.

As a first part of this study, nine children had valgus deformity of the ankle, resulting from fibular pseudoarthrosis due to post-traumatlc or sequelae of fibular osteomyelitis and treated by Langenskiolds bone grafting in four, supramalleolar corrective osteotomy in 3 and observation in 2 children. The Langenskield operation to make a bony bridge between tibial and fibular metaphyses on just below the pseudoarthrosis was effective to prevent the valgus ankle deformity in growing child, but the ankle deformity was recurred again in long-term follow-up and needed to corrective osteotomy later. The mechanism of production of the lateral malleolar elevation and of the valgus ankle deformity was removal of the physiologic thrust of growth contribution by the proximal fibular epiphysis, tethering effect of inelastic soft tissue around the pseudoarthrosls and also the early closure of lateral part of distal tibial epiphysis due to longstanding concentration of stress by increasing valgus ankle.

As a second part of study, nine children had varus and internal rotational deformitles of the ankle, resulting from fracture or fracture-separation of distal tibial epiphysis but intact the fibular and its epiphysis, and treated initially by percutaneous K-wire fixation. The distal fibula was hypertrophied, their cortex was also thickened and lateral bending deformity was severe upto 80as adaptive changes according to the severity of varus deformity. The mechanism of varus ankle deformity was the pulling down action of tibio-fibular ligament and joint capsule by the continuous fibular growth to the distal tibia which was arrested in growth by on distal tibial epiphysls the traum.

As a conclusion, the fibula in growing children was very important to develop the normal ankle and in its biomechanics, and if it is damaged in growing period, it must be restored to normal ankle and also followed them for the end of skeletal maturity.