Biomechanical Evaluation of Femoral Neck Fracture Fixation Based on Finite Element Analysis

Pauwels type III fracture, wherein the fracture plane makes an angle of 50°-70° with the transverse plane, is the most unstable femoral neck fracture. Although there are various types of internal fixation devices, including Cannulated cancellous screws (CCS), dynamic hip screw (DHS), dynamic hip screw along with anti-rotation screws (DHS+ARS), and a newly introduced femoral neck system (FNS), patients with Pauwels type III fracture often experience implant failure. There was no study investigating the performance of these internal fixators under physiological musculoskeletal loading. The objective of the present study was to compare the biomechanical performance of CCS, DHS, DHS+ARS and FNS under daily physiological activities like normal walking and stair climbing.

The unstable Pauwels type III fracture was virtually induced in a composite femur bone model and was fixed with all four internal fixators. Second-order tetrahedral elements were used to develop the FE models. The stresses, strains, and deformations of intact and reconstructed femur and implant components were compared to understand the biomechanical efficacy.

FNS showed the highest inferior axial displacement of the femoral head while DHS+ARS exhibited the least inferior axial displacement. Among the four fracture fixation systems, DHS+ARS offered the highest post-fixation stability in terms of fracture gap opening (normal walking: 0.82mm and stair climbing: 0.95mm) and contact sliding, while the performance of single hole locking plated FNS was the worst (normal walking: 2.65mm, stair climbing: 3.72mm). Based on this computational study, DHS+ARS seems to be a better performing system in Pauwels type III fracture fixation.