Variations of the Posterolateral Tubercle of the Talus: Geometric Analysis, Angular Safe Zones, and Implications for Talar Fixation Using a Three-Dimensional Simulation Model

OBJECTIVE: To investigate the prevalence of posterolateral tubercle variants and characterize the simulated safe zones and screw insertion angles for posterior-to-anterior talar screw fixation using individual 3D models from a Northeastern Thai skeletal collection. MATERIALS AND METHODS: A total of 1,106 dry tali from 553 skeletons (301 males and 252 females), aged 22-106 years, were classified according to posterolateral tubercle type. Safe zones for posterior-to-anterior (PA) screw fixation were determined for the left and right tali in both sexes using 3D simulation models, and the widest possible screw insertion angles were simulated. RESULTS: The posterolateral tubercle was classified into three types: Type 1 (almost absent, 1.36%), Type 2 (normal, 45.48%), and Type 3 (enlarged, 53.16%). In selected individual male talus models, the illustrated safe-zone configurations ranged from 20% to 50% on the left and from 30% to 60% on the right. In selected individual female talus models, the illustrated safe-zone configurations ranged from 20% to 70% on the left and from 20% to 50% on the right. CONCLUSION: The enlarged posterolateral tubercle was the most prevalent variant in the Northeastern Thai skeletal sample. The selected individual models illustrated differences in simulated safe-zone configurations and insertion angles according to side and sex. These findings may provide anatomical reference information for preoperative planning of screw fixation involving the posterolateral region of the talus.