The effect of different posterior inclinations of tibial component on tibio-femoral contact pressures after unicompartmental knee arthroplasty

Background: Different posterior inclinations of tibial component after unicompartmental knee arthroplasty (UKA) may lead to different biomechanical characteristics of knee joint. This finite element study was designed to investigate the tibio-femoral contact pressures after UKA with different posterior inclinations of tibial component. Methods Finite element model of a healthy knee joint was constructed and MB UKA models with 5 different posterior inclinations (3°, 5°, 7°, 9° and 11°) of tibial components were simulated. The maximum contact pressures of tibial plateau cartilage in the lateral compartment and polyethylene insert in the medial compartment were calculated based on the ground reaction force and the angle of the knee flexion obtained by 3D motion capture system. Results The loading ratio of medial and lateral compartment during standing stance (medial 54.49%, lateral 45.51%) and tibial anterior displacement (134N, 3.89mm) of healthy knee were basically consistent with the previous experimental data. The maximum contact pressures of the medial and lateral tibial plateau cartilage of the healthy knee during standing stance are 2.14Mpa and 1.57Mpa.At the static standing phase, the maximum contact pressures of the polyethylene insert decreased from 17.90 MPa to 17.29 MPa, and the maximum contact pressures of the tibial plateau cartilage in the lateral compartment increased from 0.81MPa to 0.92 MPa with the increase of the posterior inclination of the tibial component. At the first peak of ground reaction force, the maximum contact pressures of polyethylene insert increased from 22.37 Mpa to 25.16 Mpa, and the maximum contact pressures of tibial plateau cartilage in the lateral compartment increased from 3.03 Mpa to 3.33 Mpa with the increase of the posterior inclination of the tibial component. At the second peak of ground reaction force, the maximum contact pressures of polyethylene insert decreased from 2.34Mpa to 2.22Mpa with the increase of posterior inclination of tibial component with the increase of the posterior inclination of the tibial component. Conclusions The preoperative and postoperative finite element models of MB UKA were well established. The results showed that the maximum contact pressures of the polyethylene insert did not change significantly with the increase of the posterior inclination of the tibial prosthesis, while the maximum contact pressures of the tibial plateau cartilage of the lateral compartment increased when the posterior inclination of the tibial prosthesis was > 7°. Our results also show that the maximum contact pressures were greater with an excessive inclination angle (11°) of the tibial component, and the pressures of the tibial plateau cartilage in the lateral compartment were more concentrated on the posterior area.We suggested that excessive osteotomy should be avoided.