Evaluation of the screw position for in-situ fixation of slipped capital femoral epiphysis using finite element modelling

Abstract

Slipped Capital Femoral Epiphysis (SCFE) is the most common hip disorder in adolescents characterised by the displacement of the femoral head relative to the femoral neck through the growth plate [3]. In-situ fixation, the current standard type of treatment, stabilises the epiphysis to prevent further slippage. Although it prevents further slippage of the femoral head, the altered morphology of the proximal femur remains [4], leading to long-term complications. Recent studies have, however, revealed that bone growth can continue after fixation, suggesting potential for guided bone growth through strategic screw placement. The aim of this study is to find the optimal screw position for in-situ fixation to stimulate longitudinal bone growth in desired areas, thereby potentially improving the femur morphology and reducing SCFE severity. The study is divided into two parts: the first part focuses on modeling healthy bone growth to validate the computational approach against results from a prior study and clinical data, while the second part concentrates on SCFE analysis to explore the optimal screw position for in-situ fixation to stimulate longitudinal bone growth in desired areas. A finite element (FE) model of a femur with a mild slip was developed to predict bone growth under various screw positions. The Osteogenic Index (OI), which quantifies the expected amount of bone growth, was used to predict growth patterns. The findings indicate that the conventional center-center screw position, commonly used in surgical practice, results in minimal bone growth. Conversely, anteriorly positioned screws, particularly in the anteromedial (AM) and anterolateral (AL) regions, were associated with the most significant and beneficial growth on the posterior side of the growth plate. The expected amount of growth in the AM and AL positions was approximately 211% and 138% greater, respectively, than in the conventional center-center position. These results suggest that anterior screw placement could enhance bone growth in desired areas, potentially mitigating the severity of SCFE and improving long-term functional outcomes. These results reinforce similar findings of a prior retrospective clinical study by [2]. This study contributes to a growing body of evidence supporting the reconsideration of traditional screw placement strategies in SCFE treatment. The insights gained could inform surgical practices aimed at optimising growth modulation and improving patient outcomes. Recommendations have been given to improve the FE analysis and validation. The largest uncertainty lies in the hip contact force in SCFE patients. Further research is needed to investigate this loading for different patients and slip severities and test the influence of the loading conditions on the growth pattern. In addition, clinical trials are necessary to fully validate these findings and assess their practical implications in the treatment of SCFE.