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Radiation cross-linking increases the wear resistance of polyethylene used in total hip replacement. Radiation also generates residual free radicals, which are detrimental to long-term properties of polyethylene. Two approaches are used to stabilize the residual free radicals and terminally sterilize the components. One is postirradiation annealing with gas sterilization and the other is postirradiation melting with gamma sterilization in nitrogen. The hypothesis of the current study is that postirradiation annealing followed by gamma sterilization in nitrogen will result in more free radicals in polyethylene than gamma sterilization either in air or in nitrogen alone. To test this hypothesis, concentration of residual free radicals was quantified in polyethylene that was annealed and gamma sterilized in nitrogen and control polyethylenes gamma sterilized in air versus in nitrogen. Three crosslinked polyethylenes that were melted and gas sterilized also were included in the study. The effects of residual free radicals were studied by accelerated aging. Oxidation levels and weight loss in bidirectional pin-on-disk tests were determined before and after aging. Polyethylene that was subjected to postirradiation annealing and gamma sterilization resulted in 58% more residual free radicals than control polyethylenes. Weight loss of the annealed polyethylene increased by 16-fold on accelerated aging and had three times higher oxidation levels than that measured in control polyethylenes after aging. In contrast, polyethylenes that were stabilized with postirradiation melting and terminally gas sterilized showed no detectable residual free radicals. Accelerated aging did not affect the weight loss and oxidation levels of melted polyethylenes.

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Background: Outpatient (<24 hour stay) total joint arthroplasty (TJA) has emerged as an alternative to traditional inpatient TJA. Patient-reported outcomes in the past have revealed favorable comparisons with inpatient controls. However, a higher outpatient TJA readmission rate has been reported. The goal of our study is to report outcomes, readmissions, and unplanned access to care data on the first 1,000 TJAs performed at a de novo ambulatory surgery center (ASC). Methods: From March 2014 to May 2016, a consecutive series of 1,000 primary, total hip, and total knee arthroplasties (TKAs) were performed at a same-day surgical center. All patients were ≤66 years old, met the ASC inclusion criteria, and received preoperative training. All patients were discharged <24 hours after surgery to postoperative care suites. Oxford scores, visual analog scale for pain, patient satisfaction, ambulation, complication, and adverse events data were collected. Results: A consecutive series of 543 TKAs and 457 total hip arthroplasties (THAs) were performed. Mean age was 57.2 years (range 28 to 66 years). The TKA patients consisted of 55.2% women, whereas THA patients consisted of 45.3% women. Overall infection rate was 0.8%. Hospital readmission rate was 1.5%, and early/unplanned access to care was 11.7%. Oxford Knee and Oxford Hip scores showed 15.7 and 21.1 point improvements, respectively, whereas pain scores improved 71% for TKA and 81% for THA at 6 months postoperatively ( P < 0.01). Conclusions: Our immediate and short-term complications, readmissions, and outcomes for all patients compared favorably with published inpatient data. This study provides baseline data for quality metrics and functional outcomes for ASC-based total joint procedures.