ABSTRACT
Wear and damage of ultrahigh molecular weight polyethylene (UHMWPE) tibial inserts used in total knee arthroplasty are accelerated by oxidation. Radiation crosslinking reduces wear but produces residual free radicals adversely affecting stability. One alternative to stabilize radiation-crosslinked UHMWPE is to infuse the material with vitamin E (vit E). We investigated the properties of 100-kGy e-beam-irradiated UHMWPE that was subsequently doped with vitamin E in comparison with conventional UHMWPE. Both polymers were sterilized with gamma irradiation in vacuum packaging. Vitamin E-doped UHMWPE showed lower wear before and after aging (2.4 ± 0.5 and 2.5 ± 0.8 mg/million cycle, respectively, vs 26.9 ± 3.5 and 40.8 ± 3.0 mg/million cycle for conventional UHMWPE). Conventional UHMWPE showed oxidation after accelerated aging, and its mechanical properties were adversely affected, whereas vit E-doped UHMWPE showed no oxidation or changes in its mechanical properties. Vitamin E stabilization of radiation-crosslinked UHMWPE resulted in low wear and high oxidation resistance; it is an alternative load-bearing material for total knee applications.
Subject(s)
Antioxidants , Knee Prosthesis , Materials Testing , Polyethylenes , Vitamin E , Models, Anatomic , Prosthesis DesignABSTRACT
Wear and delamination of conventional ultrahigh-molecular-weight polyethylene (UHMWPE) components used in total knee arthroplasty can compromise long-term performance. Radiation cross-linking and melt-annealing reduced wear and increased delamination resistance of UHMWPE. An alternative material is the alpha-tocopherol-stabilized irradiated UHMWPE (alphaTPE), with improved mechanical and fatigue properties vs irradiated and melted UHMWPE. We studied the wear and delamination resistance of alphaTPE and conventional UHMWPE (direct compression molded GUR 1050 and Himont 1900) under reciprocating unidirectional motion. Wear resistance was improved, and no delamination was observed in alphaTPE. Accelerated aging did not alter the wear and delamination behavior of alphaTPE. The GUR 1050 UHMWPE showed delamination and pitting when subjected to unidirectional reciprocating motion after accelerated aging. Himont 1900 UHMWPE showed no delamination when subjected to unidirectional reciprocating motion after accelerated aging. alpha-Tocopherol-stabilized irradiated UHMWPE is advanced for use in total knee arthroplasty due to its high resistance to wear, delamination, and oxidation.
Subject(s)
Arthroplasty, Replacement, Knee/instrumentation , Biocompatible Materials , Knee Prosthesis , Materials Testing , Polyethylenes , Prosthesis Failure , Equipment Failure Analysis , Oxidation-Reduction , Prosthesis Design , alpha-TocopherolABSTRACT
Our hypothesis was that cross-linked, ultrahigh-molecular weight polyethylene (UHMWPE) stabilized with vitamin E (alpha-tocopherol) would be wear-resistant and fatigue-resistant. Acetabular liners were radiation cross-linked, doped with vitamin E, and gamma-sterilized. Hip simulator wear rate of vitamin E-stabilized UHMWPE was approximately 1 and 6 mg/million-cycles in clean serum and in serum with third-body particles, respectively, a 4-fold to 10-fold decrease from that of conventional UHMWPE. The ultimate strength, yield strength, elongation at break, and fatigue resistance of vitamin E-stabilized UHMWPE were significantly higher than that of 100 kGy-irradiated and melted UHMWPE, and were unaffected by accelerated aging. Rim impingement testing with 3.7-mm-thick acetabular liners up to 2 million-cycles showed no significant damage of the cross-linked liners compared with conventional, gamma-sterilized in inert UHMWPE, vitamin E-stabilized liners. The data indicate good in vitro wear properties and improved mechanical and fatigue properties for vitamin E-stabilized, cross-linked UHMWPE.
Subject(s)
Hip Prosthesis , Polyethylenes/chemistry , Vitamin E , Fatigue , Materials Testing , Polyethylenes/radiation effects , Prosthesis Design , Stress, Mechanical , Tensile StrengthABSTRACT
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.
