Abstract: BACKGROUND: There is still no consensus on the optimal internal fixation for the treatment of Pauwels III femoral neck fracture, and most of the related finite element analyses have been performed using a single simplified loading condition, and the biomechanical properties of commonly used internal fixation devices need to be further investigated.
OBJECTIVE: To analyze the biomechanical characteristics of Pauwels III femoral neck fractures treated with cannulated compression screw, dynamic hip screw, and femoral neck system by finite element method under different loading conditions of single-leg standing loads and sideways fall loads.
METHODS: The DICOM data of healthy adult femur were obtained by CT scanning, imported into Mimics 15.0 software to obtain the rough model of bone tissue. The data exported from Mimics were optimized by Geomagics software, and then three internal fixation models were built and assembled with the femur model according to the parameters of the clinical application of the cannulated compression screw, dynamic hip screw, and femoral neck system by using Pro/E software. Finally, the three internal fixation models were imported into Ansys software for loading and calculation to analyze the stress distribution and displacement of the femur and the internal fixation under different working conditions of single-leg standing loads and sideways fall loads, as well as the stress characteristics of the calcar femorale and Ward’s triangle.
RESULTS AND CONCLUSION: (1) Under the single-leg standing load and the sideways fall load, the proximal femoral stress of the three internal fixation models was mainly distributed above the fracture end of the femoral neck. The peak stress of the proximal femoral end, fracture end, Ward triangle, and calcar femorale of the three internal fixation models were the smallest in the femoral neck system model and the largest in the cannulated compression screw model. (2) Under the single-leg standing load and the sideways fall load, the peak displacement of the proximal femur of the three internal fixation models was all located at the top of the femoral head, and the peak displacement was the smallest in the femoral neck system model and the largest in the cannulated compression screw model. (3) The peak displacement of the three internal fixation models was all located at the top of the internal fixation device under the single-leg standing and sideways fall loading conditions, and the peak displacement values were the smallest in the femoral neck system internal fixation model and the largest in the cannulated compression screw internal fixation model. (4) The internal fixation stress of the three internal fixation models was mainly distributed in the area near the fracture end of the internal fixation device under the single-leg standing and sideways fall loads, and the peak value of internal fixation stress was the smallest in the femoral neck system model and the largest in the cannulated compression screw model. (5) These results suggest that the mechanical stability of the femoral neck system is the best, but there may be a risk of stress shielding of the fracture end and calcar femorale. The stress of the internal fixation device of the femoral neck system is more dispersed, and the risk of internal fixation break is lower.

Key words: femoral neck fracture, internal fixation, finite element analysis, biomechanics, single-leg standing, sideways fall, calcar femorale, Ward’s triangle