Finite Element Analysis of Bone Healing with Variable Fixation Locking Screws in Femoral Fracture Osteosynthesis

Femoral shaft fractures are among the most common long bone injuries, and their successful treatment requires a balance between mechanical stability and biological healing. While conventional locking screws provide rigid fixation, they may limit the micromotion necessary for callus formation. This study evaluates the mechanical performance of a hybrid fixation strategy employing Variable Fixation Locking Screws (VFLS) and conventional Locking Screws (LS) for stabilizing simple transverse femoral fractures. Using ANSYS, a finite element model was created to simulate a femoral shaft with a 2 mm fracture gap. The construct included four Variable Fixation Locking Screws (VFLS) in the proximal fragment and four standard Locking Screws (LS) distally. To simulate progressive degradation of the PLGA sleeve in the VFLS design, the Young’s modulus was reduced in stages: 100%, 75%, 50%, 25%, and 0%. For each case, strain and volume data from the callus region were used to assess the mechanical environment using volume-weighted strain analysis. The percentage of callus volume falling within the 2–10% strain range was taken as an indicator of favourable healing conditions. Results indicated that for all degradation stages except 75%, over 96% of the callus remained within this range. The 75% case showed an abnormal drop in strain, suggesting excessive stiffness during partial degradation. Overall, the VFLS system provided stable mechanical conditions throughout the simulated healing process, with only a temporary deviation at the intermediate stage.