A finite element analysis of the optimal longitudinal screw trajectory for Sanders II and Sanders III calcaneal fractures fixed with percutaneous screws

BACKGROUND: In recent years, percutaneous screw fixation technology has been extensively utilized in the management of displaced intra-articular calcaneal fractures. However, there remains a lack of consensus regarding the optimal design of screw trajectories to achieve maximal biomechanical strength. The objective of the present study was to identify the optimal screw trajectory for percutaneous screw fixation of calcaneal fractures through the application of finite element analysis. METHODS: The finite element analysis was used in this study. Six fracture models (Sanders IIA, B, C and IIIAB, AC, BC) were constructed according to the Sanders classification system. Based on the injury mechanism of calcaneal fractures, the anatomical characteristics of the calcaneus, and the results of preliminary experiments, four different screw fixation methods were designed to simulate the internal fixation of calcaneal fractures. RESULTS: In the six fracture models, the maximum stress on the calcaneal bone and the maximum displacement between the fracture blocks in the study group 1 and study group 2 were both less than those in control groups 1 and control groups 2. These differences were particularly significant in the II C, III AC, and III BC fracture models. In the II A fracture model, the screw stress in the study group 1 and study group 2 was higher than in control groups 1 and control groups 2. Conversely, in the II B and III AB fracture models, the differences in screw stress among the four fixation methods were minimal. In the II C, III AC, and III BC fracture models, the screw stress in the study group 1 and study group 2 was lower than that in control groups 1 and control groups 2. Notably, none of the screw stresses exceeded the threshold for internal fixation failure (600 mPa). CONCLUSION: In the treatment of Sanders II and Sanders III calcaneal fractures with percutaneous screw fixation technique, the lateral longitudinal screw should be fixed from the calcaneal tubercle to the anterior process of the calcaneus, and the medial longitudinal screw should be fixed from the calcaneal tubercle along the medial wall to the calcaneal sustentaculum tali. This configuration is associated with optimal biomechanical stability.