How does total knee replacement technique influence polyethylene wear?

ABSTRACT

In knee prostheses, wear is inherent to the tribology of the imperfectly congruent surfaces, one in chromium-cobalt alloy, the other in polyethylene. It is a multifactorial phenomenon, involving the properties of the respective materials and implant design, but also implant functioning, as determined by the implantation technique. There are still dark corners in the implantation charge book, especially concerning minimal insert thickness, the adjustment of tibiofemoral alignment and ligament balance. A review of the literature revealed consensus regarding minimal insert thickness (8mm), tibiofemoral alignment (to be kept within 5° on either side of the neutral axis) and ligament balance (identical collateral ligament tension in both extension and flexion spaces). Finer adjustment seems desirable. Tibiofemoral alignment is probably customizable according to individual patient morphology and weight. The rotational alignment of the components should allow harmonious patellar engagement. Classic ligament balance rules underestimate sagittal laxity, which needs checking to prevent paradoxical movement accelerating polymer delamination. Navigation techniques or specific ancillaries can help optimize implant component alignment. Control of sagittal laxity may require specific adaptation, notably in the flexion space. Improved implantation technique could postpone wear onset until beyond the 10th or even 20th postoperative year, barring material failure for other reasons.