Biomechanical study of a new cannulated screw for Pauwels type III femoral neck fractures

Abstract

Background A new cannulated screw for the treatment of Pauwels type III femoral neck fracture (FNF) was developed and its biomechanical stability was analyzed by finite element analysis and mechanical tests to provide a new approach for the clinical treatment of Pauwels type III FNF. Methods A Pauwels III femoral neck fracture model with an angle of 70° was constructed using medical engineering software such as Mimics, Geomagic, and Hypermesh. Two parallel inverted triangular cannulated screw finite element models were established to simulate surgical fixation: three conventional cannulated screw models(CCS), and two upper cannulated screw + one new cannulated screw models(NCS). The biomechanical properties of the 2 fixation methods were compared and analyzed under the same loading and constraint conditions. An unstable femoral neck fracture model was made using a composite femur (Sawbone) at a Pauwels 70° angle. Reduction and fixation models of Pauwels III FNF were made according to CCS and NCS fixation methods. and the compression displacement of the femur was tested, then the load-displacement curve was used to calculate the stiffness and compare the advantages and disadvantages of the two internal fixation methods. Results In the computer-simulated reconstruction of the inverted triangular cannulated screw fixation model for Pauwels type III FNFs, the NCS model outperformed the CCS model in terms of strain and stress distribution. And the peak stress of the 2 groups appeared in the middle section of the screw closest to the femoral spur, close to the fracture line. In the experimental mechanical model of Pauwels type III FNF, under the same loading condition, the NCS group has smaller distance of femoral deformation and fracture end displacement than the CCS group, and from the perspective of stiffness, the former group had greater stiffness and smaller compression distance under the same vertical load. Conclusions The new cannulated screws provide good biomechanical stability for the treatment of Pauwels type III FNFs, which provides a new choice for the treatment of young patients with vertical fracture of femoral neck.