Shannon L Rowell1, Orhun K Muratoglu1,2. 1. Harris Orthopaedics Laboratory, Massachusetts General Hospital, Boston, MA. 2. Department of Orthopaedic Surgery, Harvard Medical School, Boston, MA.
Abstract
BACKGROUND: Antioxidant stabilized highly crosslinked ultra-high molecular weight polyethylene (UHMWPE) components have been in clinical use since 2008. In vitro testing has shown excellent oxidation resistance, wear resistance, mechanical properties, and fatigue strength. In this study, we analyzed surgically retrieved components to investigate in vivo behavior and changes in the material. METHODS: Fifteen surgically retrieved, vitamin E-stabilized, and radiation crosslinked UHMWPE components were analyzed to determine their oxidative stability, extent of lipid absorption in vivo, free radical content, hydroperoxide index, and extent of visible wear damage after in vivo service (0.1-36.6 months). RESULTS: Retrievals showed no significant carbonyls at the time of surgical removal, while free radical content was observed to decay with increasing in vivo duration. There was no increase in hydroperoxide index. Lipid penetration increased with time. Ex vivo oxidation was not observed after 18 months of aging in air at room temperature. CONCLUSIONS: The free-radical scavenging activity of the vitamin E appears to successfully prevent both in vivo and ex vivo oxidation for short durations, while reducing free radical content overall. Without an increase in hydroperoxides, the oxidation cascade initiated by radiation-induced and lipid-derived free radicals appears to have been inhibited. Further investigation is required with longer duration implants.
BACKGROUND: Antioxidant stabilized highly crosslinked ultra-high molecular weight polyethylene (UHMWPE) components have been in clinical use since 2008. In vitro testing has shown excellent oxidation resistance, wear resistance, mechanical properties, and fatigue strength. In this study, we analyzed surgically retrieved components to investigate in vivo behavior and changes in the material. METHODS: Fifteen surgically retrieved, vitamin E-stabilized, and radiation crosslinked UHMWPE components were analyzed to determine their oxidative stability, extent of lipid absorption in vivo, free radical content, hydroperoxide index, and extent of visible wear damage after in vivo service (0.1-36.6 months). RESULTS: Retrievals showed no significant carbonyls at the time of surgical removal, while free radical content was observed to decay with increasing in vivo duration. There was no increase in hydroperoxide index. Lipid penetration increased with time. Ex vivo oxidation was not observed after 18 months of aging in air at room temperature. CONCLUSIONS: The free-radical scavenging activity of the vitamin E appears to successfully prevent both in vivo and ex vivo oxidation for short durations, while reducing free radical content overall. Without an increase in hydroperoxides, the oxidation cascade initiated by radiation-induced and lipid-derived free radicals appears to have been inhibited. Further investigation is required with longer duration implants.
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