Does Kinematic Alignment Increase Polyethylene Wear Compared With Mechanically Aligned Components? A Wear Simulation Study

Abstract

Background Kinematic alignment is an alternative approach to mechanical alignment. Kinematic alignment can restore the joint line to its prearthritic condition, and its advocates have suggested it may be associated with other benefits. But this alignment approach often results in tibial components that are placed in varus and femoral components that are placed in valgus alignment, which may result in an increased risk of component loosening because of wear. Like malaligned implant components, kinematically aligned knee implants could increase wear in vivo, but we lack comparative data about wear behavior between these approaches. Questions/purposes (1) Do the different alignment approaches (kinematic, mechanical, and purposefully malaligned components) result in different wear rates in a wear simulator? (2) Do the different alignment approaches lead to different worn areas on the polyethylene inserts in a wear simulator? (3) Do the different alignment approaches result in different joint kinematics in a wear simulator? Methods Mechanical alignment was simulated in a forcecontrolled manner with a virtual ligament structure according to the International Organization for Standardization (ISO 14243-1) using a knee wear simulator. To simulate kinematic alignment, flexion-extension motion, internalexternal torque, and the joint line were tilted by 4°, using a novel mechanical setup, without changing the force axis. The setup includes bearings with inclinations of 4°so that the joint axis of 4°is determined. To verify the angle of 4°, aThe study was financially supported by the nonprofit research foundation Stiftung Endoprothetik, Hamburg, Germany (S 01/20). One of the authors (TR) certifies receipt of personal payments, during the study period, in an amount of less than USD 10,000 from Zimmer Biomet Holdings, in an amount less than USD 10,000 from Aesculap AG/AQ Solutions GmbH, and in an amount less than USD 10,000 from DePuy Synthes as honoraria for lectures. One of the authors (JPK) certifies receipt of personal payments, during the study period, in an amount of less than USD 10,000 from Mathys AG and less than USD 10,000 USD from DePuy Synthes as honoraria for lectures. None of these payments influenced the design and results of the current study. All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research® editors and board members are on file with the publication and can be viewed on request. Clinical Orthopaedics and Related Research® neither advocates nor endorses the use of any treatment, drug, or device. Readers are encouraged to always seek additional information, including FDA approval status, of any drug or device before clinical use. Ethical approval was not sought for the present study.

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].…”

Mechanical alignment tolerance of a cruciate-retaining knee prosthesis under gait loading—A finite element analysis

“…On the coronal plane, the joint line of the knee prosthesis was rotated around the AP axis to simulate the malalignment. Therefore, the flexion-extension axis and the internal-external rotation axis were not parallel or perpendicular to the joint line ( Schroeder et al, 2022 ) ( Figure 3A ). The femoral component was flexed or extended along the FE axis before the gait loading to indicate the malalignment on the sagittal plane ( Figure 3B ).…”

CORR Insights®: Does Kinematic Alignment Increase Polyethylene Wear Compared With Mechanically Aligned Components? A Wear Simulation Study

“…Schroeder et al [4] investigated the influence of joint alignment (mechanical alignment, kinematic alignment, and 4° of malalignment) on wear performance using a knee wear simulator. The concern about kinematic alignment is that the slight amount of mechanical varus it usually generates might be a source of excess wear; the authors found that alignment with up to 4° of component inclination in the setting of kinematically aligned TKA kept the amount of wear generation comparable to that observed with mechanically aligned TKAs.…”

“…Proponents of kinematic alignment believe this approach results in kinematics after TKA that more closely resemble those of a normal knee. High-quality clinical research has found no difference in clinical outcome between kinematic and mechanical alignment [9], but few studies I’m aware of have assessed the wear performance of these two alignment techniques [4].…”

“…It is unclear how the kinematics or wear performance of various jigs can be verified for different alignments. Virtual ligament structures play an important role in controlling force in the wear test, with input values calculated according to the mechanical axis, which is the standard position in the ISO 14243-1 [3] (and was the position used by Schroeder et al [4]). However, quantifying ligament conditions under different alignments, especially kinematic alignment, needs to be more specific.…”