Abstract: BACKGROUND: The traditional fixation method for femoral neck fractures is three hollow screws inverted triangle fixation, and the optimal fixation method for femoral neck fractures that have not achieved anatomical reduction is inconclusive.
OBJECTIVE: To compare the biomechanical properties of cannulated screws internal fixation for sub-capitated femoral neck fracture with different reduction qualities based on finite element analysis. 
METHODS: The three-dimensional digital model was reconstructed using CT data of the proximal femur from a healthy male volunteer. The femur was modeled to sub-capitated femoral neck fractures. Fracture models were divided into anatomical reduction group, coxa vara group, and coxa valgus group. All fracture model groups were transferred using the standard group, screw depression group, and screw elevation group. A vertical downward stress of 1 400 N was applied to the femoral head at the top of the acetabulum. The displacement and stress distribution of the femur and internal fixator under different fixation methods were observed, and the maximum stress and displacement of the femur and fixator were compared. 
RESULTS AND CONCLUSION: (1) For anatomical reduction femoral neck fracture, the peak stress of fixation in the standard group, screw depression group and screw elevation group was 41.35, 31.27 and 43.32 MPa, respectively. The maximum peak stress of the femur was found on the screw elevation group (28.58 MPa), and the standard group had the maximum peak displacement. (2) During hip varus, the stresses in the three subgroups were relatively dispersed and even. The peak stress of the femur in the standard group was the smallest, but the peak displacement was the largest. The stability of fixation might be poor. The peak displacement of the femur in the screw depression group was the smallest. (3) In the hip valgus, obvious screw stress concentration appeared in the screw depression group, and the peak displacement was the largest among the three subgroups, and an in-out-in phenomenon appeared. The peak stress of the screws in the screw elevation group was the largest among the three subgroups, but the peak displacement was the smallest. (4) It is concluded that for sub-capitated femoral neck fractures that are completely anatomically reduced, it is recommended to use standard inverted triangular nails for fixation. When the hip varus and hip valgus occur within the allowable range of the reduction standard, it is recommended to use the inverted triangle screw to fix it by rotating the corresponding angle in the same direction as the hip varus or valgus.

Key words: femoral neck fracture, internal fixation, finite element analysis, reduction quality, biomechanics