Evaluation of Oxidation and Fatigue Damage of Retrieved Crossfire Polyethylene Acetabular Cups

Background Highly crosslinked and thermally treated polyethylenes were clinically introduced to reduce wear and osteolysis. Although the crosslinking process improves the wear performance, it also introduces free radicals into the polymer that can subsequently oxidize. Thermal treatments have been implemented to reduce oxidation; however, the efficacy of these methods with regard to reducing in vivo oxidative degradation remains to be seen. Polyethylene oxidation is a concern because it can compromise the ultimate strength and ductility of the material. Questions/purposes We analyzed the oxidation, oxidation potential, and mechanical behavior of thermally treated highly crosslinked polyethylene retrieved acetabular liners. Methods Three hundred seven acetabular liners were collected from consecutive revision surgeries at six institutions over a 10-year period. Twenty-four were sterilized using nonionizing methods, 43 were sterilized in an inert environment, 80 were highly crosslinked and annealed, and 160 were highly crosslinked and remelted. Oxidation and oxidation potential were assessed by Fourier transmission infrared spectroscopy. Mechanical behavior was assessed by the small punch test. Results Oxidation and hydroperoxide (oxidation potential) indices were elevated in the annealed and gamma inert sterilized groups compared with those of the remelted liners and uncrosslinked gas sterilized controls, particularly at the rim. We also detected an increase in oxidation over time at the bearing surface of the remelted group. Ultimate strength of the polyethylene at the bearing surface was negatively correlated with implantation time for the annealed liners. Conclusions Within the first decade of implantation, the clinical outlook for first-generation highly crosslinked polyethylene remains promising. However, ongoing research continues to be warranted for first-generation highly crosslinked polyethylene bearings to monitor the implications of elevated oxidation at the rim of annealed liners as well as to better understand the subtle changes in oxidation at the bearing surface of remelted liners that occur in vivo.

Section: Discussionmentioning

confidence: 87%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Do First-generation Highly Crosslinked Polyethylenes Oxidize In Vivo?

MacDonald

Sakona

Ianuzzi

et al. 2011

“…FTIR spectroscopy results were reported using a ketone peak height ratio technique (ketone peak height, 1713-1718 cm À1 ) normalized to the 1368-cm À1 peak height thickness proxy (1365-1371 cm À1 ) [8,9]. The oxidation value reported for each retrieved insert is the maximum ketone value measured 0.5 to 2.5 mm below the articular surface of the bearing (maximum articular oxidation).…”

Section: Methodsmentioning

confidence: 99%

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

Berry

Currier

Mayor

et al. 2012

Self Cite

Background In the mid to late 1990s, to sterilize UHMWPE bearings, manufacturers changed from gammairradiation-in-air (gamma-air) sterilization, which initiated oxidation leading to bearing fatigue, to gamma-irradiation sterilization in an inert environment (gamma-inert). The change to gamma-inert sterilization reportedly prevented shelf oxidation before implantation but not in vivo oxidation. Questions/purposes We asked: (1) Has the change to gamma-inert sterilization prevented shelf oxidation that led to early in vivo fatigue damage in gamma-air-sterilized tibial inserts? And (2) has the change to gamma-inert sterilization prevented the occurrence of fatigue secondary to in vivo oxidation? Methods We rated 183 retrieved gamma-air-and 175 retrieved gamma-inert-sterilized tibial inserts for clinical fatigue damage and analyzed 132 gamma-air-and 174 gamma-inert-sterilized tibial inserts for oxidation by Fourier transform infrared spectroscopy. Results Oxidation led to decreased mechanical properties in shelf-aged gamma-air-sterilized tibial inserts. Barrier packaging prevented shelf oxidation in gamma-inertsterilized tibial inserts. Gamma-air-and gamma-inertsterilized inserts oxidized in vivo. Fatigue damage (delamination) occurred more frequently in inserts retrieved after longer time in vivo. Longer in vivo time correlated with higher oxidation and more accumulated cycles of use. Conclusions Published oxidation projections suggest gamma-inert-sterilized tibial inserts would reach the critical oxidation for the onset of fatigue after 11 to 14 years in vivo. These retrievals appear to follow the projected oxidation trends. Frequency of fatigue damage increased with increasing oxidation. Clinical Relevance Fatigue of tibial inserts becomes more likely, especially in active patients, after more than a decade of good clinical performance.

“…Oxidative degradation of some of the first generation of CLPE formulations has been considered a potential limiting factor for the long-term performance of THA [7,28]. During gamma irradiation (for crosslinking or for sterilization), free radicals formed in the PE molecular structure cause embrittlement through a cascading oxidation reaction [7]. Hence, the incorporation of the antioxidant vitamin E (a-tocopherol) has been proposed to prevent oxidation and has been introduced into clinical use [5,15,34].…”

Section: Introductionmentioning

confidence: 99%

Multidirectional Wear and Impact-to-wear Tests of Phospholipid-polymer-grafted and Vitamin E-blended Crosslinked Polyethylene: A Pilot Study

Kyomoto

Moro

Takatori

et al. 2015

Background Modifying the surface and substrate of a crosslinked polyethylene (CLPE) liner may be beneficial for high wear resistance as well as high oxidative stability and excellent mechanical properties, which would be useful in contributing to the long-term performance of orthopaedic bearings. A grafted poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) layer on a vitamin E-blended crosslinked PE (HD-CLPE[VE]) surface may provide hydrophilicity and lubricity without compromising the oxidative stability or mechanical properties. Questions/purposes (1) Will the modifications (PMPC grafting and vitamin E blending) affect the lubrication characteristics of the CLPE surface? (2) Will the modifications affect wear resistance? (3) Will the modifications affect fatigue resistance? Methods We investigated the effects of surface and substrate modifications (PMPC grafting and vitamin E blending) on the wear and fatigue fracture of thin CLPE samples. For each of the untreated and PMPC-grafted CLPE surfaces with and without vitamin E blended (four groups), wettability and lubricity surface analyses were conducted as well as multidirectional wear and impact-towear tests using a pin-on-disk testing machine. Results The water wettability and lubricity (CLPE [mean ± 95% confidence interval]: 23.2°± 1.8°, 0.005 ± 0.001; HD-CLPE[VE]: 26.0°± 2.3°, 0.009 ± 0.003) of the PMPCgrafted surfaces were greater (p \ 0.001) than that (CLPE: 90.3°± 1.2°, 0.067 ± 0.015; HD-CLPE[VE]: 90.8°± 2.0°, 0.063 ± 0.008) of the untreated surface regardless of vitamin E additives. It was observed that the PMPC grafting (CLPE: 0.23 ± 0.06 mg; HD-CLPE[VE]: 0.05 ± 0.10 mg) was associated with reduced gravimetric wear (CLPE: 0.53 ± 0.08 mg, p = 0.004 HD-CLPE[VE]: 0.23 ± 0.07 mg, p = 0.038) in the multidirectional wear test. The PMPC-grafted surface characteristics did not appear to affect the impact fatigue resistance regardless of vitamin E blending. Conclusions PMPC grafting improved the surface hydrophilicity and lubricity, and it reduced the gravimetric wear in terms of multidirectional sliding. It did not result in differences in terms of the impact-to-unidirectional sliding regardless of vitamin E blending. Further research is needed to evaluate the wear resistance of PMPC-grafted HD-CLPE(VE) in long-term hip simulator tests under normal