Advances in the processing, sterilization, and crosslinking of ultra-high molecular weight polyethylene for total joint arthroplasty

398

282

Background Highly crosslinked polyethylene (HXLPE) was introduced to reduce wear and osteolysis in total joint arthroplasty. While many studies report wear and osteolysis associated with HXLPE, analytical techniques, clinical study design and followup, HXLPE formulation and implant design characteristics, and patient populations differ substantially among investigations, complicating a unified perspective. Questions/purposes Literature on first-generation HXLPE was summarized. We systematically reviewed the radiographic wear data and incidence of osteolysis for HXLPE in hip and knee arthroplasty. Methods PubMed identified 391 studies; 28 met inclusion criteria for a weighted-averages analysis of two-dimensional femoral head penetration rates. To determine the incidence of osteolysis, we estimated a pooled odds ratio using a random-effects model.Results Weighted-averages analyses of femoral head penetration rates in HXLPE liners and conventional UHMWPE liners resulted, respectively, in a mean twodimensional linear penetration rate of 0.042 mm/year based on 28 studies (n = 1503 hips) and 0.137 mm/year based on 18 studies (n = 695 hips). The pooled odds ratio for the risk of osteolysis in HXLPE versus conventional liners was 0.13 (95% confidence interval, 0.06-0.27) among studies with minimum 5-year followup. We identified two clinical studies of HXLPE in TKA, preventing systematic analysis of outcomes. Conclusions HXLPE liner studies consistently report lower femoral head penetration and an 87% lower risk of osteolysis. Reduction in femoral head penetration or osteolysis risk is not established for large-diameter ([ 32 mm) metallic femoral heads or ceramic femoral heads of any size. Few studies document the clinical performance of HXLPE in knees.

Section: History and Development Of Hxlpementioning

confidence: 99%

Section: History and Development Of Hxlpementioning

confidence: 99%

History and Systematic Review of Wear and Osteolysis Outcomes for First-generation Highly Crosslinked Polyethylene

Kurtz

Gawel

Patel

2011

398

282

“…In the past decade, highly crosslinked and thermally treated polyethylenes were introduced to reduce wear and osteolysis [3,17,22]. First-generation highly crosslinked polyethylenes were thermally stabilized by annealing (heating below the melting point) or by remelting (heating above the melting point) [17] to reduce free radical concentrations and thereby reduce oxidation.…”

Section: Introductionmentioning

confidence: 99%

Do First-generation Highly Crosslinked Polyethylenes Oxidize In Vivo?

MacDonald

Sakona

Ianuzzi

et al. 2011

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.

“…In the mid to late 1990s, manufacturers changed to gammainert sterilization of UHMWPE bearings from gamma-air sterilization, which reportedly initiates oxidation leading to bearing fatigue [9,11]. Gamma-inert sterilization prevented shelf oxidation before implantation but not subsequent in vivo oxidation.…”

Section: Discussionmentioning

confidence: 99%

“…For more than four decades, gamma-irradiation has been the industry standard sterilization method [11]. In the mid to late 1990s, manufacturers changed from gamma sterilization in air (gamma-air) to gamma sterilization in an inert environment (gamma-inert; eg, ArCom 1 , gamma vacuum foil, gamma-N2, etc).…”

Section: Introductionmentioning

confidence: 99%

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

Berry

Currier

Mayor

et al. 2012

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.