Abstract
Implant wear and osteolysis have been a major cause of failure of total knee implants. In the mid-1990s, manufacturers recognised the impact of oxidation on wear with implants sterilised by gamma irradiation in air and changed their methods of sterilisation. This has resulted in a dramatic reduction in wear. In retrieval studies, non-irradiated polyethylene has not shown the fatigue type of failure associated with oxidation. The percentage of revisions done at the Anderson Clinic for polyethylene wear for osteolysis has dropped from 44% in the late 1990s to 4% in the past decade. With the continued use of polyethylene free of oxidation, we anticipate a further reduction in the need for revision surgery secondary to wear and osteolysis.
Highly cross-linked polyethylene was introduced to further reduce wear with total knee implants. Higher levels of irradiation used increases crosslinking in the polyethylene but the material strength is reduced. Although volumetric wear is reduced, the wear particles are smaller in size and potentially more bio-reactive. The Manufacturer And User Device Experience Database (MAUDE) reports describe early implant breakage and osteolysis of highly cross-linked polyethylene inserts. Implants that were highly crosslinked with quenched free radicals demonstrate increased levels of oxidation after retrieval unlike, never implanted components “off-the-shelf”. Backside wear remains a concern as non-modular implants have better long-term survivorship compared to their modular counterparts. These reports should temper enthusiasm for using highly cross-linked material in knees or modular tibial components until longer term clinical and retrieval studies have been completed.
