Kinematic Alignment in Total Knee Arthroplasty Reduces Polyethylene Contact Pressure by Increasing the Contact Area, When Compared to Mechanical Alignment—A Finite Element Analysis

Abstract

Unrestricted Kinematic alignment (KA) in total knee arthroplasty (TKA) replicates the joint line of each patient by adjusting the cuts based on the anatomy of the patient. Mechanical alignment (MA) aims to restore a neutral mechanical axis of the leg, irrespective of the joint line orientation. The purpose of the present study was to compare contact pressure and contact areas of the polyethylene (PE) bearing surface as well as von Mises stress of the PE-tibial tray interface for MA and KA in the same patient, using CT data and finite element analysis. Finite element models were created from lower leg CT scans of 10 patients with knee osteoarthritis with different phenotypes. Mechanical PE properties were experimentally determined by tensile tests on dumbbell specimens. For numerical simulation purposes an adjusted non-linear material model with the maximum load to failure of 30.5 MPa, was calibrated and utilized. Contact pressure points were the deepest parts of the polyethylene inlay. Contact pressures were either very similar or were increased for MA knees throughout the gait cycle. KA either increased or had a comparable contact area, compared to MA. KA and MA produced comparable von Mises stresses, although both alignments breached the failure point of 30.5 MPa in all 3 valgus knees. This might indicate a higher probability of failure at the inlay-tibial baseplate interface. By maintaining the joint line orientation, KA reduces or has comparable contact pressures on the PE bearing surface by increasing or maintaining the contact area throughout one gait cycle in a validated finite element analysis model in 10 different knee phenotypes. The von Mises stress on the PE-tibial component interface was comparable, except for the valgus knees, where the load to failure was achieved in both alignment strategies and slightly higher stresses were observed for KA. Further studies for different knee phenotypes are needed to better understand the pressure changes depending on the alignment strategy applied.

A robotic‐assisted simulation of kinematic alignment in TKA leads to excessive valgus and internal rotation in valgus knees

“…Other possible concerns of adding internal rotation to the femoral component include the creation of a more pronounced change in native tibiofemoral kinematics as demonstrated by a recent cadaver study by Heyse et al as well as higher quadriceps requirements as shown by Nettrour et al [13,25]. A recent inite element analysis by Klasan et al conirms the risk of using kinematic alignment in valgus knees by demonstrating an increased failure rate [19]. Another important inding is that approximately 18% of patients with neutrally aligned knees would also be at increased risk of patellofemoral maltracking by using robotic-assisted kinematic alignment due to the same reason.…”

“…Other possible concerns of adding internal rotation to the femoral component include the creation of a more pronounced change in native tibiofemoral kinematics as demonstrated by a recent cadaver study by Heyse et al as well as higher quadriceps requirements as shown by Nettrour et al [13, 25]. A recent finite element analysis by Klasan et al confirms the risk of using kinematic alignment in valgus knees by demonstrating an increased failure rate [19].…”

Superiority of kinematic alignment over mechanical alignment in total knee arthroplasty during medium‐ to long‐term follow‐up: A meta‐analysis and trial sequential analysis

“…Several factors may have contributed to such outcomes. Klasan demonstrated that KA, compared with MA, reduced polyethylene contact pressure, while Schroeder's results suggested that KA did not increase polyethylene wear [17,36]. Moreover, with the implementation of intraoperative navigation and roboticassisted systems, non-human-induced outliers have decreased, leading to enhanced precision [4,14,37,40,42].…”

Application strategy of finite element analysis in artificial knee arthroplasty

“…(C) Reprinted with permission from ref. Klasan et al (2022) (Copyright 2022; MDPI, Basel, Switzerland).…”

“… Kang et al (2020) studied ligament-preserving prostheses and found that KA had better mobility and even stress distribution than MA. Klasan et al (2022) established a finite element model for 10 patients with knee osteoarthritis to simulate TKA with mechanical alignment and kinematic alignment. The results showed a larger contact area and lower contact pressure on the polyethylene insert in TKA patients treated with kinematic alignment than in those treated with mechanical alignment ( Figure 1C ), but there was no significant difference in von Mises stress between the polyethylene insert and the tibia.…”