title: In vivo oxidation and surface damage in retrieved ethylene oxide-sterilized total knee arthroplasties.
abstract: BACKGROUND
  Gas sterilization (eg, ethylene oxide [EtO] and gas plasma) was introduced for polyethylene to reduce oxidation due to free radicals occurring during radiation sterilization. Recently, oxidation has been observed in polyethylenes with undetectable levels of free radicals, which were expected to be oxidatively stable. It is unclear whether in vivo oxidation will occur in unirradiated inserts sterilized with EtO.
  
  
  OBJECTIVE
  We analyzed the oxidation, mechanical behavior, and surface damage mechanisms of tibial inserts of a single design sterilized using EtO.
  
  
  METHODS
  We collected 20 EtO-sterilized tibial inserts at revision surgeries. We assessed oxidative using Fourier transform infrared spectroscopy and mechanical properties using the small punch test. Surface damage was assessed using damage scoring techniques and micro-CT.
  
  
  RESULTS
  Oxidation indexes were low and uniform between the regions. The subtle changes did not affect the mechanical properties of the polymer. The dominant surface damage modes included burnishing, abrasion, and third-body wear. There was no evidence of delamination in the retrievals.
  
  
  CONCLUSIONS
  The retrieved EtO-sterilized UHMWPE retrievals remained stable with respect to both oxidative and mechanical properties for up to 10 years in vivo. We did observe slight measurable amounts of oxidation in the inserts; however, it was far below levels that would be expected to compromise the strength of the polymer.
  
  
  CONCLUSIONS
  Due to the stable oxidative and mechanical properties, EtO-sterilized tibial components appear to be an effective alternative to gamma-sterilized inserts, at least in short-term implantations.
authors: Implant Research Center, School of Biomedical Engineering, Science, and Health Systems, Drexel University, 3401 Market Street, Suite 300, Philadelphia, PA 19104, USA. dm68@drexel.edu
authors: Daniel
authors: D
authors: MacDonald
authors: Josa
authors: J
authors: Hanzlik
authors: Peter
authors: P
authors: Sharkey
authors: Javad
authors: J
authors: Parvizi
authors: Steven M
authors: SM
authors: Kurtz
mesh_terms: D000328:Adult; D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects / Q000295:instrumentation*; D001696:Biomechanical Phenomena; D020878:Device Removal; D004202:Disinfectants / Q000009:adverse effects*; D005027:Ethylene Oxide / Q000009:adverse effects*; D005260:Female; D005740:Gases; D006801:Humans; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D010084:Oxidation-Reduction; D015143:Philadelphia; D011095:Polyethylenes / Q000009:adverse effects / Q000737:chemistry; D011474:Prosthesis Design; D012086:Reoperation; D017550:Spectroscopy, Fourier Transform Infrared; D013242:Sterilization / Q000379:methods*; D013314:Stress, Mechanical; D013499:Surface Properties; D013997:Time Factors; D055114:X-Ray Microtomography
chemical_list: D004202:Disinfectants; D005740:Gases; D011095:Polyethylenes; C111601:ultra-high molecular weight polyethylene; D005027:Ethylene Oxide