POLYETHYLENE DAMAGE IN TOTAL KNEES AND USE OF HIGHLY CROSSLINKED POLYETHYLENE

Abstract

Tibial inserts and patellar components used in total knee arthroplasty (TKA) are made of ultra-high molecular weight polyethylene. (In the present article, UHMWPE and terminology will be used interchangeably to refer to the same polymer, i.e., ultra-high molecular weight polyethylene.) The mechanisms of damage at the tibiofemoral and patellofemoral articulations consist of delamination, adhesive wear, and abrasive wear of the polyethylene component. These damage mechanisms contribute to the formation of a visible scar on the articular surfaces of the tibial insert and the patellar component. Creep and plastic deformation, both of which induce permanent deformation, also contribute to the scar on the articular surfaces and on the backside of modular polyethylene components. Creep accumulates for approximately the first two years of in vivo use and then reaches a steady state. Plastic deformation occurs rapidly due to the yielding of the polyethylene surface when the joint is loaded. Among these damage modes, delamination is the primary cause of most polyethylene-related total knee failures. Delamination can result in the loss of geometric conformity, can alter the pattern of load distribution, and can eventually result in accelerated implant failure by disengagement or fracture of the tibial insert or wear-through. To a lesser extent, adhesive/abrasive wear contributes to implant failure mainly by generating particulate debris that results in periprosthetic osteolysis1-11. In some instances, the amount of bone loss after TKA is great, leading to component loosening or fracture9. Revision surgery in these cases is particularly difficult, often requiring special component augments or bone grafts12. The causes of delamination and adhesive/abrasive wear are multifactorial. These damage mechanisms are influenced by the extent of oxidative embrittlement of the polyethylene resulting from gamma sterilization in air13-15 and the stress state of the components16, …