Oxidation and oxidation potential in contemporary packaging for polyethylene total joint replacement components

Abstract

The packaging and chemical stability of both conventional and highly crosslinked polyethylene (PE) components available for clinical use in Italy were analyzed. A total of 100 sterilized PE components were entered by 18 orthopedic manufacturers into the study. Six of the manufacturers were Italian and the remaining were based in Europe or America. Hydroperoxide, oxidation, and trans-vinylene levels within the PE components were characterized using Fourier-transform infrared spectroscopy (FTIR). None of the 31 gas-sterilized components had detectable free radicals, hydroperoxide content, or oxidation. Among radiation-sterilized inserts, the highest oxidation and hydroperoxide levels were associated with gas-permeable and polymer-barrier packaging. To the authors' knowledge, this is the first study that relates elevated oxidation and hydroperoxide content in gamma-sterilized PE components to certain types of contemporary, polymeric barrier packaging.

Gamma-irradiation Sterilization in an Inert Environment: A Partial Solution

“…Never-implanted gamma-sterilized tibial inserts, removed from air-permeable packages after years of shelf aging, showed oxidation of the UHMWPE during shelf aging resulted in degraded mechanical properties [4,9] (Table 6). We confirmed barrier packaging of gamma-sterilized tibial inserts prevented preimplantation shelf oxidation for up to 5 years [6]. By preventing preimplantation oxidation, gamma-inert-sterilized inserts were not embrittled by shelf oxidation, and delamination fatigue damage was essentially eliminated in barrier-packaged inserts over the first 5 years in vivo.…”

“…Shelf storage time before implantation was a concern for gamma-air-sterilized inserts [4,7,9] where shelf oxidation led to early in vivo fatigue damage. Some early barrier packaging did not effectively prevent shelf oxidation [6], but the change from gamma-air to gamma-inert sterilization largely prevented the shelf oxidation that led to fatigue after less than 4 years in vivo [5]. In vivo oxidation was predicted to increase exponentially with time [9,12].…”

“…Studies of never-implanted gamma-inert-sterilized acetabular liners and tibial inserts suggested gamma-inert sterilization in a barrier package prevented shelf oxidation before implantation [4,6], although some instances of leaking in early multilayer polymer film packaging leading to shelf oxidation were reported [6]. Short-term retrieval studies showed sterilization in an inert environment did not prevent in vivo oxidation.…”

Gamma Inert Sterilization: A Solution to Polyethylene Oxidation?

“…Even so, totally oxygen-free atmospheres were not necessarily achieved. In this regard, changes in the distribution of oxidation and hydroperoxides in irradiated polyethylene components recently have been associated with differences in the irradiation and packaging conditions, namely, radiation dose rate, irradiation temperature, packaging type, and packaging environment, even in the cases of conventional and highly crosslinked polyethylenes 32 . Orthopaedic manufacturers improved the first-generation packaging technology that had been developed for gamma inert sterilization of polyethylene components and introduced second-generation packaging to improve isolation from oxygen 11 .…”

Does Cyclic Stress Play a Role in Highly Crosslinked Polyethylene Oxidation?

“…On the other hand, internal stresses developed during cyclic loading might result in chain scission and, therefore, creation of free radicals that eventually would take part in the oxidation process. Insights into the oxidation potential, that is, hydroperoxide species, on cyclic loading could help ascertain the route of mechanically initiated oxidation [4].…”