The finite element analysis study of the impact of single and double lag screw fixation on ankle fractures of different sizes.

In clinical practice, the choice of single vs. double screw fixation for posterior malleolus fractures (PMF) is theoretically unclear, particularly concerning the size-stability relationship. This study, employing Finite Element Analysis (FEA), assesses biomechanical stability in PMF of varying sizes under both fixation methods. Utilizing a 3D model based on CT scans, we simulated fractures with 10-50% fragment sizes and applied a 600 N force to mimic the single-leg stance. Our evaluation focused on screw Von Mises stress (VMS) and fracture relative displacement (RD). Results show that stability increases with fragment size for both fixation types. Single screw fixation is comparable to double screw in fragments up to 25%, but in larger fragments, double screw significantly enhances stability. This suggests that for fragments over 25%, double screw fixation is preferable, marking a critical threshold for PMF stability.