Finite element analysis of different repair methods of Vancouver B1 periprosthetic fractures after total hip arthroplasty

Objective: To use finite element analysis to study the stability of different fixation methods used to repair Vancouver type B1 periprosthetic fractures occurring after total hip arthroplasty (THA). Methods: An artificial femur was used as the basis for the solid model; U2 series femoral stem (United Orthopedic Corporation, Hsinchu, Taiwan) was used for modelling of the prosthesis; and the modelling of the cable plate, wires and screws was based on information given in the manufacturer's catalogue (Zimmer, Warsaw, IN, USA). The analysis model was constructed using the ANSYS software, and all material settings were based on literature values. A six-orifice cable plate, unicortical screws (20 mm long and 4.5 mm in diameter) and bicortical screws (50 mm long and 4.5 mm in diameter) were constructed. Four analysis models were defined. The basic model had a plate and three cable wires above the fracture line and two bicortical screws below the fracture line. In the second model, two unicortical screws were added above the fracture line. In the third model, three wires were added below the fracture line. In the fourth model, both the proximal screws of the second model and the distal wires of the third model were added to the basic model. To ensure that the numerical values produced by analysis reached convergence, mesh convergence was tested. Results: Adding two proximal unicortical screws to the basic Ogden construct (plate, proximal wires and distal screws) lessened displacement of the fracture and decreased the von Mises stress on the repair. Adding three distal wires to the basic construct had no noticeable effect. Conclusion: Better fixation power is achieved by using both proximal and distal screws (the locking-plate concept) in treating Vancouver type B1 periprosthetic fracture after THA.