Abstract
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.
Highlights
Total knee arthroplasty (TKA) is an effective surgical intervention for end-stage knee osteoarthritis in which the diseased articulating surfaces of the knee joint are replaced with artificial components to relieve pain and restore the normal knee function [1]
Previous studies suggest that a minimum thickness of 6 to 8 mm is required to minimize the contact stresses within the tibial insert surface [8,9], applying the conventional 2 mm increments; these increments allow surgeons to identify the effect of PE insert thickness variations on the soft-tissue tension and intraoperative kinematics based on knee laxity trials [10,11]
The peak medial collateral ligament (MCL), lateral collateral ligament (LCL), and posterior cruciate ligament (PCL) forces increased by 38 N, 74 N, and 125 N, respectively, as PE insert thickness changed from 9 mm to 11 mm; the corresponding peak force increase for a 4 mm greater thickness relative to the reference case was 80 N, 157 N, and 286 N
Summary
Total knee arthroplasty (TKA) is an effective surgical intervention for end-stage knee osteoarthritis in which the diseased articulating surfaces of the knee joint are replaced with artificial components to relieve pain and restore the normal knee function [1]. Previous studies suggest that a minimum thickness of 6 to 8 mm is required to minimize the contact stresses within the tibial insert surface [8,9], applying the conventional 2 mm increments; these increments allow surgeons to identify the effect of PE insert thickness variations on the soft-tissue tension and intraoperative kinematics based on knee laxity trials [10,11]. Following this recommendation, some authors argue that the insertion of thicker PE components is likely to prevent accelerated wear and early surgical failure [12]
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