High cycle in vitro hip wear of and in vivo biological response to vitamin E blended highly crosslinked polyethylene

Wear testing of 40 mm diameter acetabular liners made of vitamin E blended highly-crosslinked polyethylene (VE-HXPE) was conducted for 100 million cycles (Mc) and the wear rate was compared to those of conventional gamma-sterilized polyethylene (CPE) and melt-annealed highly-crosslinked polyethylene (HXPE) liners. Particles of blended VE-HXPE and HXPE particles were injected into the knee capsules of white rabbits to evaluate potential local and systemic effects. VE-HXPE demonstrated volumetric wear rate < 3 mm3/Mc representing an order of magnitude reduction from that of 32 mm diameter CPE liners. The wear debris distribution shifted towards bigger sizes at later stages (>50Mc) of testing, indicating a further reduction in number of particles generated and thus the potential to further reduce the incidence of osteolysis during clinical use. Histological analyses of the liver, spleen and lymph nodes exhibited no evidence of systemic toxicity in rabbits injected with blended VE-HXPE particles. Small clusters of particles were found within synovial membranes and encapsulated in macrophages of rabbits injected with HXPE and VE-HXPE particle suspensions. The degrees of the inflammatory response to VE-HXPE and HXPE particles were not significantly different.