Which is the safe position of femoral component in coronal plane in mobile-bearing unicompartmental knee arthroplasty? a finite element-based study

Abstract

Abstract Background Apply finite element analysis to explore the influence of different femoral prosthesis positions on the stress of the polyethylene bearing to determine the safe position of the femoral prosthesis in mobile-bearing Unicompartmental Knee arthroplasty. Methods A normal knee joint model was established and verified. The femoral component were designed with intorsion13 °,intorsion6 °, 0°(neutral position),extorsion6°,extorsion13°,and were combined into 5 three⁃dimensional finite element models of medial unicompartmental knee arthroplasty. A 1000 N load was applied along the femoral mechanical axis. The von Mises cloud stress distribution was observed. Moreover, the high contact stress of femoral prosthesis, the lateral compartment load ratio, the upper surface of the polyethylene liner, and the femoral cartilage in the lateral compartment was measured. Compared with the neutral position (6°and 13°intorsion or extorsion of the femoral prosthesis) to find the appropriate position of the femoral component. Results The maximum contact stress of the femoral prosthesis from the neutral position to the internal and external rotation of the femur, tibia prosthesis and meniscal liner gradually increase. When the femoral prosthesis internal and external rotation at 13°,the maximum contact stress of the femoral prosthesis increased by 3.21 MPa and 1.17 MPa, respectively, the maximum contact stress of the polyethylene liner increased by 4.46 MPa and 3.22 MPa, respectively. The maximum contact stress increased with the internal and external rotation angles, which suggested that it was unsafe for the femoral prosthesis to rotate within 10°. Conclusion Static knee biomechanics after mobile bearing unicompartmental knee arthroplasty can be affected by femoral component alignment༎During unicompartmental knee arthroplasty surgery, femoral prosthesis rotations within 10°are cannot be considered as appropriate for placing the femoral prosthesis in mobile—bearing unicompartmental knee arthroplasty, femoral prosthesis rotations more than 6°will increasing the risk of postoperative complications and may reduce the long-term survival rate of the prosthesis.