Objective To study the effects of different posterior slope installations of unicompartmental knee arthroplasty(UKA)prostheses on the loading and motion of the knee joint and insert wear.Methods A combined approach involving the UKA musculoskeletal multibody dynamic,finite element,and wear prediction models was used to investigate the effects of five different posterior slope installation positions of the UKA prosthesis on the postoperative knee joint force and motion,insert contact stress,linear wear depth,and wear volume.Results At a 0° posterior slope,the maximum von Mises stress of the insert was 24.84 MPa,maximum contact stress was 47.61 MPa,and volumetric wear after 5 million cycles(MC)was 47.29 mm3.As the posterior slope angle of the UKA prosthesis increased,the internal rotation and posterior translation during the gait cycle increased,the medial joint force during the swing phase increased,the von Mises and contact stresses of the insert after 5 MC decreased significantly,and the wear area,maximum linear wear depth,and volumetric wear volume of the insert were consequently reduced.Compared to the 0° posterior slope,the linear wear depths of the insert at the 3°,5°,and 7° posterior slopes decreased by 17.8％,19.2％,and 20.6％,respectively.The volumetric wear volumes of the inserts decreased by 24.5％,30.9％,and 34.3％,respectively.Conclusions Installing a UKA prosthesis with a posterior slope exceeding 3° significantly increases internal rotation and posterior translation during the gait cycle,further reducing the articular volumetric wear of the polyethylene insert.

The clinical performance and failure issues are significantly influenced by prosthetic malposition in unicompartmental knee arthroplasty (UKA). Uncertainty exists about the impact of the prosthetic joint line height in UKA on tibial insert wear. In this study, we combined the UKA musculoskeletal multibody dynamics model, finite element model and wear model to investigate the effects of seven joint line height cases of fixed UKA implant on postoperative insert contact mechanics, cumulative sliding distance, linear wear depth and volumetric wear. As the elevation of the joint line height in UKA, the medial contact force and the joint anterior-posterior translation during swing phase were increased, and further the maximum von Mises stress, contact stress, linear wear depth, cumulative sliding distance, and the volumetric wear also were increased. Furthermore, the wear area of the insert gradually shifted from the middle region to the rear. Compared to 0 mm joint line height, the maximum linear wear depth and volumetric wear were decreased by 7.9% and 6.8% at -2 mm joint line height, and by 23.7% and 20.6% at -6 mm joint line height, the maximum linear wear depth and volumetric wear increased by 10.7% and 5.9% at +2 mm joint line height, and by 24.1% and 35.7% at +6 mm joint line height, respectively. UKA prosthetic joint line installation errors can significantly affect the wear life of the polyethylene inserted articular surfaces. Therefore, it is conservatively recommended that clinicians limit intraoperative UKA joint line height errors to -2-+2 mm.
Humans ; Arthroplasty, Replacement, Knee ; Knee Joint ; Knee Prosthesis ; Mechanical Phenomena ; Polyethylene ; Osteoarthritis, Knee/surgery* ; Tibia/surgery* ; Biomechanical Phenomena