Finite element analysis of the effect of cannulated screw placement and drilling frequency on femoral neck fracture fixation

Background: Positioning of the implanted cannulated screw is paramount for stable femoral neck fracture fixation. To avoid overdrilling, the aim of this study is to determine the optimum configuration of three cannulated screws employed in femoral neck fracture fixation.

Methods: Using a CT scan from a 28 year old healthy male, several models of femoral neck fracture fixation were developed using finite element analysis. After drilling small holes (in either fixed or random patterns) for screw insertion, the mechanical stresses on the screws were compared for three fracture types.

Results: The inverted isosceles triangle was found to be the best screw configuration. Using finite element analysis, the upper limit of drilling frequency and the maximum stress on the screws for 30°, 50°, and 70° drilling were 14, 16, and 19 times and 46.1MPa, 61.9MPa, and 51.0MPa, respectively. The upper limit of drilling frequency and the maximum stress on the screws for subcapital type, transcervical type, and basicervical type were 14, 16, and 40 times and 24.7MPa, 61.9MPa, and 113.5MPa, respectively.

Conclusions: Results of this study had supported the use of the inverted isosceles triangle as the best screw configuration for femoral neck fracture fixation. Screw position, Pauwels angle, and drilling frequency can all affect the mechanical strength of femoral neck fracture fixation.