Impact of intraprosthetic drilling on the strength of the femoral stem in periprosthetic fractures: A finite element investigation

Treatment of periprosthetic femur fractures after total hip arthroplasty remains a major challenge in orthopedic surgery. Recently, a novel surgical technique using intraprosthetic screw fixation has been suggested. The purpose of this study was to evaluate the influence of drilling the femoral hip stem on integrity and strength of the implant. The hypothesis was that intraprosthetic drilling and screw fixation would not cause the load limit of the prosthesis to be exceeded and that deformation would remain within the elastic limit. A sawbone model with a conventional straight hip stem was used and a Vancouver C periprosthetic fracture was created. The fracture was fixed with a nine-hole less invasive stabilization system plate with two screws drilled and inserted through the femoral hip stem. Three different finite element models were created using ANSYS software. The models increased in complexity including joint forces and stress risers from three different dimensions. A variation of drilling positions was analyzed. Due to the complexity of the physiological conditions in the human femur, the most complex finite element model provided the most realistic results. Overall, significant changes in the stresses to the prosthesis caused by the drilling procedure were observed. While the stresses at the site of the bore hole decreased, the load increased in the surrounding stem material. This effect is more pronounced and further the holes were apart, and it was found that increasing the number of holes could counteract this. The maximum load was still found to be in the area of the prosthesis neck. No stresses above the load limit of titanium alloy were detected. All deformations of the prosthesis stem remained in the elastic range. These results may indicate a potential role for intraprosthetic screw fixation in the future treatment of periprosthetic femur fractures. © Institution of Mechanical Engineers