Oxidation in Retrieved, Never-Irradiated UHMWPE Bearings: What Can We Learn About in Vivo Oxidation?

Background: Published analyses of never-irradiated, ethylene oxide (EtO)-sterilized tibial inserts and EtO- and gas plasma (GP)-sterilized acetabular ultra-high molecular weight polyethylene (UHMWPE) retrievals demonstrated minimal UHMWPE in vivo oxidation, whereas another analysis of EtO-sterilized acetabular liners found elevated oxidation linked with in vivo stresses. This study explored whether never-irradiated UHMWPE bearings are (1) oxidized by the in vivo environment, and (2) more likely to oxidize in higher-stress articulations (knee, ankle, shoulder).

Methods: An institutional review board-approved retrieval archive was queried for never-irradiated, EtO- and GP-sterilized UHMWPE bearings received at revision from 2001 to 2021.

What factors drive polyethylene wear in total knee arthroplasty? : results of a large retrieval series.

Aims: Wear of the polyethylene (PE) tibial insert of total knee arthroplasty (TKA) increases the risk of revision surgery with a significant cost burden on the healthcare system. This study quantifies wear performance of tibial inserts in a large and diverse series of retrieved TKAs to evaluate the effect of factors related to the patient, knee design, and bearing material on tibial insert wear performance.

Methods: An institutional review board-approved retrieval archive was surveyed for modular PE tibial inserts over a range of in vivo duration (mean 58 months (0 to 290)).

Tobacco Exposure Is Associated With Extremely Low Polyethylene Oxidation in Total Knee Arthroplasty Components.

Background: We evaluate whether patient exposures such as tobacco use are associated with high systemic or local in vivo oxidative state and with increased in vivo polyethylene oxidation.

Methods: We performed a case-control study which evaluated clinical factors associated with high systemic or local in vivo oxidative state among patients whose implants have been identified as demonstrating either extreme or minimal oxidation by our implant retrieval laboratory. Analysis of more than 2500 tibial inserts from explanted total knee arthroplasty demonstrated a wide spectrum of polyethylene oxidation.

Analysis of Failed Ankle Arthroplasty Components.

Background:: Although advances in joint-replacement technology have made total ankle arthroplasty a viable treatment for end-stage arthritis, revision rates for ankle replacements are higher than in hip or knee replacements. The questions asked in this study were what can retrieved ankle devices demonstrate about ankle arthroplasty failures and how can understanding the causes of these failures inform clinical decisions for current and future ankle arthroplasty patients?

Methods:: An IRB-approved retrieval laboratory received retrieved components and surgeon-supplied reason for revision from 70 total-ankles (7 designs, including 5 currently marketed designs) from 2002 to 2018. These retrievals were rated for clinical wear and damage.

Effectiveness of anti-oxidant polyethylene: What early retrievals can tell us.

The optimum UHMWPE orthopedic implant bearing surface must balance wear, oxidation, and fatigue resistance. Antioxidant polyethylene addresses free radicals, resulting from irradiation used in cross-linking, that could oxidize and potentially lead to fatigue damage under cycles of in vivo use. This study evaluates what short-term antioxidant UHMWPE retrievals can reveal about: (1) oxidation-resistance and (2) fatigue-resistance of these new materials.

A Novel Technique for Assessing Antioxidant Concentration in Retrieved UHMWPE.

Background: Antioxidants added to UHMWPE to prevent in vivo oxidation are important to the long-term performance of hip and knee arthroplasty. Diffused vitamin E antioxidant polyethylene raised questions about potential in vivo elution that could cause inflammatory reactions in periprosthetic tissues and also potentially leave the implant once again prone to oxidation. Currently, there is no information on the elution, if any, of antioxidants from implant polyethylene materials in vivo.

Oxidation and other property changes of a remelted highly crosslinked UHMWPE in retrieved tibial bearings.

This study examined retrieved UHMWPE tibial bearings made from a remelted highly crosslinked (HXL) UHMWPE to determine whether the material is chemically stable in vivo. Retrieved tibial components were measured for changes in ketone oxidation and crosslink density. Oxidation increased with in vivo duration, and a significant decrease in crosslink density with increased mean ketone oxidation index was observed.

Comparison of Wear and Oxidation in Retrieved Conventional and Highly Cross-Linked UHMWPE Tibial Inserts.

Two groups of retrieved tibial inserts from one manufacturer's knee system were analyzed to evaluate the effect of a highly cross-linked bearing surface on wear and in vivo oxidation. The two groups ((1) conventional gamma-inert sterilized and (2) highly cross-linked, coupled with the same rough (Ra=0.25) Ti-6Al-4V tray) were matched with statistically similar in vivo duration and patient variables.

Oxidation and other property changes of retrieved sequentially annealed UHMWPE acetabular and tibial bearings.

This investigation analyzed retrieved sequentially crosslinked and annealed (SXL) ultra-high molecular weight polyethylene bearings to determine whether the material is chemically stable in vivo. A series of retrieved tibial and acetabular components were analyzed for changes in ketone oxidation, crosslink density, and free radical concentration. Oxidation was observed to increase with in vivo duration, and the rate of oxidation in tibial inserts was significantly greater than in acetabular liners.

Crosslink density, oxidation and chain scission in retrieved, highly cross-linked UHMWPE tibial bearings.

Irradiated, thermally stabilized, highly cross-linked UHMWPE bearings have demonstrated superior wear performance and improved in vitro oxidation resistance compared with terminally gamma-sterilized bearings, yet retrieval analysis reveals unanticipated in vivo oxidation in these materials despite fewer or no measurable free radicals. There has been little evidence to date that the oxidation mechanism in thermally stabilized materials is the same as that in conventional materials, and so it is unknown whether oxidation in these materials is leading to chain scission and a degradation of mechanical properties, molecular weight, and crosslink density. The aim of this study was to determine whether measured in vivo oxidation in retrieved, highly cross-linked tibial bearings corresponds with a decreasing crosslink density.

Gamma-irradiation sterilization in an inert environment: a partial solution.

Background: In the mid to late 1990 s, to sterilize UHMWPE bearings, manufacturers changed from gamma-irradiation-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.

Evaluating the suitability of highly cross-linked and remelted materials for use in posterior stabilized knees.

Posterior stabilized (PS) knee designs are a popular choice for cruciate sacrificing knee arthroplasty procedures. The introduction of PS inserts fabricated from highly cross-linked and remelted Ultra High Molecular Weight Polyethylene (UHMWPE) has recently generated concern as these materials have been shown to possess reduced mechanical properties. This study investigated whether highly cross-linked and remelted UHMWPE material (referred to as XRP) can be expected to perform similarly to historical gamma-air polyethylene, which has suffered few reported incidences of tibial post failure.

Rim cracking of the cross-linked longevity polyethylene acetabular liner after total hip arthroplasty.

Background: Studies have suggested that cross-linked polyethylene bearings reduce wear rates from 40% to 100% compared with conventional polyethylene. However, the reduced mechanical properties of highly cross-linked polyethylene have the potential to be a limiting factor in device performance. We reviewed a series of retrieved acetabular liners with a fracture of the superior rim to assess the factors that played a role in their failure.

Evaluation of oxidation and fatigue damage of retrieved crossfire polyethylene acetabular cups.

Background: Crossfire cross-linked polyethylene is produced differently from other cross-linked polyethylene materials; a below-melt-temperature annealing process is used with the goal of avoiding compromised mechanical properties. The present study was performed to evaluate retrieved Crossfire acetabular cups to determine whether they had oxidized and to what extent oxidation might have influenced their clinical performance.

Methods: Eleven acetabular cups were received at retrieval and a twelfth acetabular cup was received two years post-retrieval over a period of four years.

Unilateral tibial polyethylene liner failure in bilateral total knee arthroplasty--bilateral retrieval analysis at 8 years.

This is a report of a unique case of bilateral simultaneous total knee arthroplasties in which one tibial liner failed dramatically, whereas the other liner showed minimal evidence of wear. This unique case allows isolation of component factors as the primary contributing etiology to failure. The differentiating characteristic was the method of sterilization and the shelf life of the polyethylene liner.

In vivo oxidation of gamma-barrier-sterilized ultra-high-molecular-weight polyethylene bearings.

gamma-Barrier packaging is shown to be effective in preventing oxidation of polyethylene during shelf storage and in addressing the problem of early fatigue failure seen in gamma-air-sterilized bearings with long shelf-storage before implantation. The series of gamma-barrier retrievals studied suggests that oxidation occurs in the body via the same mechanism as seen in gamma-air-sterilized bearings. A critical oxidation level is identified above which polyethylene bearings are susceptible to fatigue damage after sufficient cycles of use.

Comparison of cross-linked polyethylene materials for orthopaedic applications.

Cross-linked polyethylenes are being marketed by orthopaedic manufacturers to address the problem of osteolysis caused by polyethylene particulate wear debris. Wear testing of these cross-linked polyethylenes in hip simulators has shown dramatic reduction in wear rate compared with standard ultrahigh molecular weight polyethylene, either gamma irradiated in air or nitrogen - or ethylene oxide-sterilized. However, this reduction in wear rate is not without cost.

Rapid polyethylene failure of unicondylar tibial components sterilized with gamma irradiation in air and implanted after a long shelf life.

Background: The mechanical toughness of polyethylene that has been sterilized by gamma irradiation in air decreases after a long shelf life. The purpose of the present study is to report the high failure rate after unicondylar knee replacements performed with polyethylene bearings that had been sterilized with gamma irradiation in air and implanted after a shelf life of < or = 4.4 years.