Origin and factors for overgrowth in pediatric fractures of the femoral shaft after flexible intramedullary nail fixation.

Background: Leg length discrepancy is a common complication following flexible intramedullary nail (FIN) fixation for femoral shaft fractures in adolescents. This retrospective study was designed to evaluate the possible cause of femoral overlengthening in children with femoral shaft fracture. Methods: We retrospectively included 138 patients diagnosed with femoral shaft fractures between June 2012 and December 2022 and reported the clinical/radiological outcomes after at least half a year of surgery. We have introduced a new parameter, distal physis growth proportion (DPGP), which can be used to predict the origin of femoral growth. Results: The mean DPGP value of 138 samples was 50.9%, of which 24 (17.4%) were greater than 70% and 114 (82.6%) were less than 70%. In the group with nail-canal diameter ratio (NCD) values greater than 60%, the proportion of patients with DPGP values exceeding 70% was significantly higher compared to the group with NCD values less than 60%. However, there was no significant difference between gender, fracture side, fracture type, mode of reduction, associated craniocerebral injury or the distance from fracture site to distal articular surface of femur. Conclusions: In children with femoral shaft fractures treated with FIN fixation, the number of patients with DPGP lesser than 70% far exceeded the number of patients with DPGP greater than 70%, indicating the significant role of fracture end stimulation in femoral lengthening.