The optimal angle of screw for using cement-screw technique to repair tibial defect in total knee arthroplasty: a finite element analysis

Background The cement-screw technique is a convenient method to repair tibial plateau defects in primary and revision total knee arthroplasty (TKA). However, the optimal angle of screw insertions is unknown. This study aimed to perform a finite element analysis (FEA) to determine the optimal screw angle for the repair of tibial plateau defects in TKA. Methods Seven FEA models were set and two common different defects (defect 1: area < 12%, depth < 12 mm; defect 2: area > 12%, depth > 12 mm) were simulated. One screw was used in defect 1, and one or two screws were used in defect 2. Screws were parallel to the proximal cortical bone (oblique screw) or perpendicular to the upper surface (vertical screw) of the tibia. Contact stresses on cancellous bone in different areas were determined. Maximum principal stress on the cancellous bone around each screw was also compared. Results The FEA models showed that stresses on the surface of cancellous bone in tibial defect (0.13-0.39 MPa) and stress focus spot (0.45 MPa) around the screw were lower when one vertical screw was used in defect 1. The stresses on the surface of cancellous bone in tibial defect (0.09-0.44 MPa), stresses in the medial tibial plateau (0.14-0.21 MPa), and stress focus spot around the screws were lowest (0.42 MPa and 1.37 MPa) when two vertical screws were used in defect 2, followed by of one vertical and one oblique (0.16-0.48 MPa; 0.15-0.21 MPa; 1.63 MPa and 1.11 MPa). No other statistically significant differences were found. Conclusions Either for one or two screws, those perpendicular to the upper surface achieve better stability than those parallel to the proximal cortical bone of the tibia. If two vertical screws cannot be performed, one vertical and one oblique is also acceptable.