Introduction:The objectives of this study were to identify the biomechanical factors involved in the occurrence of upper femoral epiphysiolysis through a series of cases and a review of the literature and to study the biomechanical factors of stability of the upper femoral epiphysis after percutaneous screw fixation.Methods:This was a retrospective longitudinal study conducted in the orthopedic department at the Tunis Children's Hospital over a period of 7 years. The evaluation of the results was clinical by the PMA score and radiological by the calculation of the residual tilt angle. Results:The main biomechanical factor involved in the occurrence of EFS was obesity. It was identified in 58% of the cases with an adiposo-genital morphotype that represented 11%.Conclusion: Knowledge of the biomechanical factors at the time of placement of the cephalic screw is the guarantee of a stable osteosynthesis.