ABSTRACT
The oxidation resistance of irradiated ultra-high molecular weight polyethylene (UHMWPE) components used in total joint arthroplasty can be improved by adding alpha-tocopherol (vitamin E) through diffusion. To ensure long-term oxidative stability, a minimum alpha-tocopherol concentration needs to be maintained throughout these components. Migration of alpha-tocopherol out of the components is one mechanism that could compromise long-term oxidative stability. We hypothesized that alpha-tocopherol could elute out during standard implant fabrication steps such as cleaning as well as during in vivo use. We doped 85 kGy irradiated UHMWPE with alpha-tocopherol at 120 degrees C and homogenized at 120 degrees C. We determined the extent of elution of alpha-tocopherol or its effect on oxidative stability following cleaning in isopropyl alcohol (IPA) and following 5 million cycles (MC) of simulated normal gait in bovine serum. There was no significant elution of alpha-tocopherol in repeated and prolonged cleaning in IPA as measured by average surface and bulk alpha-tocopherol concentrations. There was no change in the oxidative stability following 5 MC of hip simulator testing, indicating minimal elution during simulated normal gait.
Subject(s)
Joint Prosthesis , Polyethylenes/radiation effects , alpha-Tocopherol/administration & dosage , Animals , Biocompatible Materials , Cattle , Drug Stability , Humans , In Vitro Techniques , Materials Testing , Oxidation-Reduction , Spectroscopy, Fourier Transform Infrared , alpha-Tocopherol/pharmacokineticsABSTRACT
Irradiation decreases the wear of ultra-high molecular weight polyethylene (UHMWPE) but generates residual free radicals, precursors to long-term oxidation. Melting or annealing is used in quenching free radicals. We hypothesized that irradiated and once-annealed UHMWPE would oxidize while irradiated and melted UHMWPE would not, and that the oxidation in the former would increase wear. Acetabular liners were real-time aged by immersion in an aqueous environment that closely mimicked the temperature and oxygen concentration of synovial fluid. After 95 weeks of real-time aging, once-annealed components were oxidized; the melted components were not. The wear rate of the real-time aged irradiated and once-annealed components was higher than the literature reported values of other contemporary highly cross-linked UHMWPEs. Single annealing after irradiation used with terminal gamma sterilization may adversely affect the long-term oxidative stability of UHMWPE components.