The thickness of the tibial polyethylene (PE) insert is a critical parameter to ensure optimal soft-tissue balancing in the intraoperative decision-making procedure of total knee arthroplasty (TKA). However, there is a paucity of information about the kinetic response to PE insert thickness variations in the tibiofemoral (TF) joint, and subsequently, the secondary effects on the patellofemoral (PF) biomechanics. Therefore, the purpose of this study was to investigate the influence of varying PE insert thickness on the ligament and TF compressive forces, as well as on the PF forces and kinematics, after a cruciate-retaining TKA. A previous patient-specific musculoskeletal model of TKA was adapted to simulate a chair-rising motion in which PE insert thickness was varied with 2 mm increments or decrements compared to the reference case (9 mm), from 5 mm up to 13 mm. Greater PE insert thickness resulted in higher ligament forces and concurrently increased the TF compressive force by 21% (13 mm), but slightly unloaded the PF joint with 7% (13 mm) while shifting the patella distally in the trochlear groove, compared to the reference case. Thinner PE inserts showed an opposite trend. Our findings suggest that the optimal PE insert thickness selection is a trade-off between the kinetic outcomes of the TF and PF joints.

Robotic-assisted total knee arthroplasty can attain highly accurate implantation. However, the target for optimal positioning of the components remains debatable. One of the proposed targets is to recreate the functional status of the pre-diseased knee. The aim of this study was to demonstrate the feasibility of reproducing the pre-diseased kinematics and strains of the ligaments and, subsequently, use that information to optimize the position of the femoral and tibial components. For this purpose, we segmented the pre-operative computed tomography of one patient with knee osteoarthritis using an image-based statistical shape model and built a patient-specific musculoskeletal model of the pre-diseased knee. This model was initially implanted with a cruciate-retaining total knee system according to mechanical alignment principles; and an optimization algorithm was then configured seeking the optimal position of the components that minimized the root-mean-square deviation between the pre-diseased and post-operative kinematics and/or ligament strains. With concurrent optimization for kinematics and ligament strains, we managed to reduce the deviations from 2.4 ± 1.4 mm (translations) and 2.7 ± 0.7° (rotations) with mechanical alignment to 1.1 ± 0.5 mm and 1.1 ± 0.6°, and the strains from 6.5% to lower than 3.2% over all the ligaments. These findings confirm that adjusting the implant position from the initial plan allows for a closer match with the pre-diseased biomechanical situation, which can be utilized to optimize the pre-planning of robotic-assisted surgery.