Introduction. We have previously demonstrated that peroxide crosslinked vitamin E-blended UHMWPE maintains its clinically-required wear and mechanical properties [1]. This material can potentially be used as an irradiation-free bearing surface for TJA. However, using organic peroxides in medical devices requires a thorough examination of tissues in contact with the implant. For this study we crosslinked polyethylene using five times the needed concentration of peroxide (2,5-Dimethyl-2,5-di(t-butylperoxy)-hexyne-3 or P130), followed by implantation to determine implant biocompatibility, and pre and post implant peroxide residual contents. Methods. The study was performed after institutional approval following ISO standard 10993–6. Study groups: not crosslinked (0.2 (1050) VE), crosslinked (0.2 VE (1050)/5% P130) and crosslinked-high temperature melted (HTM) (0.2 VE (1050)/5% P130). Materials were blended and consolidated, machined (2.5 diameter × 2.5 cm height), sterilized and implanted in the dorsum New Zealand white rabbits. Pre and post implantation FTIR was performed. Two samples were implanted in each rabbit; n=6 samples were included for each group. After 4 weeks, samples were explanted, analyzed using FTIR, and subcutaneous tissues processed for histological analysis. Results. FTIR absorbances at 914cm. −1. , 1169cm. −1. , and the OH absorbance at 3450cm. −1. showed differences between materials (Fig 1A). There was a significant increase in the absorbance at 914 for the non-crosslinked and crosslinked samples after explantation (p = 2.77E–17, p = 4.22E–23, Fig 1B). There was a significant decrease in all peroxide related absorbances after explantation for the crosslinked and HTM samples (p < 0.05, Fig 1B). Before implantation, these absorbances were significantly higher in the crosslinked and crosslinked/HTM samples than those in the non crosslinked sample (p<0.05, Fig 2A). Peroxide related absorbances of the crosslinked sample were also significantly higher than those of the crosslinked/HTM sample (p<0.05, Fig 2A). After explantation, the crosslinked samples had significantly higher absorbances than both the non crosslinked and crosslinked/HTM samples (p < 0.05, Fig 2A). All peroxide related absorbances of the crosslinked/HTM samples were significantly higher than those of the non crosslinked sample (p < 0.05, Fig 2A). The non crosslinked sample showed no significant differential between these absorbances at implantation and after retrieval. The crosslinked sample had the largest differential between the total peak absorbances before implantation and retrieval at 914cm. −1. The crosslinked/HTM samples had the largest differential between the total peak absorbances before and after implantation for both 1169cm. −1. and the OH absorbances (Fig 2B). All explants were recovered after four weeks in vivo (Fig 3A). No difference was found in the histological analysis of the tissue characterized by a synovial-like lining with signs of fibrosis around the implants (Fig 3B). Discussion. The main challenge of this study was identifying pre and postoperative implant peroxide residual peaks via FTIR. We wanted to ensure that peroxide was present in implants before implantation, to ensure their elution into tissues. Conclusions. Peroxide crosslinked polyethylene stabilized with vitamin E can potentially be used as an alternate bearing surface. Irradiation-free processing could result in cost-effectiveness and more accurate cross-linking of polyethylene implants

Purpose. Cross-linking of polyethylene greatly reduces its wear rate in hip simulator studies. We conducted a systematic review and meta-analysis of randomized controlled trials comparing cross-linked to conventional polyethylene liners for total hip arthroplasty to determine if there is a clinical reduction of: 1) wear rates, 2) radiographic osteolysis, and 3) need for total hip revision. Method. A systematic search of MEDLINE, EMBASE, and COCHRANE databases was conducted from inception to May 2010 for all trials involving the use of cross-linked polyethylene for total hip arthroplasty. Eligibility for inclusion in the review was: use of a random allocation of treatments; a treatment arm receiving cross-linked polyethylene and a treatment arm receiving conventional polyethylene for total hip arthroplasty; and use of radiographic wear as an outcome measure. Eligible studies were obtained and read in full by two co-authors who then independently applied the Checklist to Evaluate a Report of a Nonpharmacological Trial to each study. Pooled mean differences were calculated for the following continuous outcomes: bedding-in, linear wear rate, three dimensional linear wear rate, volumetric wear rate, and total linear wear. Pooled risk ratios were calculated for radiographic osteolysis and revision hip arthroplasty. Results. The literature search strategy identified 194 potential studies of which 12 met inclusion criteria. All studies reported a significant reduction in radiographic wear with cross-linked polyethylene. Pooled mean differences for linear wear rate, three dimensional linear wear rate, volumetric wear rate, and total linear wear were all significantly reduced for cross-linked polyethylene. The risk ratio for radiographic osteolysis was 0.40 (95% C.I. of 0.27 to 0.58; p<0.01; I2=0%), favoring cross-linked polyethylene. There were no significant differences in need for revision total hip arthroplasty or amount of bedding-in. Conclusion. Cross-linked polyethylene liners demonstrate reduced radiographic wear and osteolysis up to 8 years after implantation. Follow up is not long enough to show a difference in need for revision total hip arthroplasty. Cross-linked polyethylene should be considered for young patients undergoing total hip arthroplasty