title: Shelf age of the polyethylene tibial component and outcome of unicondylar knee arthroplasty.
abstract: BACKGROUND
  A recent report linked shelf-aging of unicondylar polyethylene tibial components with accelerated fatigue wear and rapid failure. We retrospectively reviewed our experiences with another unicondylar knee system to investigate the relationship between the shelf age of the polyethylene components and clinical outcome.
  
  
  METHODS
  One hundred Single Compartment Replacement unicompartmental knee arthroplasties were performed with cement between 1990 and 1996. The median shelf age for the polyethylene inserts was 1.7 years. At the time of the review, four knees had been lost to follow-up, sixteen were in patients who had died, and nineteen had been revised. Sixty-one knee replacements remained in situ at a mean and standard deviation of 8 +/- 2 years postoperatively.
  
  
  RESULTS
  With revision as the end point, Kaplan-Meier survivorship analysis demonstrated a six-year rate of survival of 96% when the shelf age of the insert was less than the median shelf age but only 71% when the median shelf age was exceeded. Fatigue wear was identified on all retrieved components except for two that had shelf ages under one year and had been revised within three years. At four to six years of clinical follow-up, the group of knees in which the median shelf age had been exceeded also had poorer Knee Society knee scores and function scores.
  
  
  CONCLUSIONS
  Aging on the shelf accelerated fatigue failure of polyethylene inserts sterilized with gamma irradiation in air and compromised our intermediate-term clinical outcomes with this unicondylar knee replacement system. Attention to the relationship between the shelf age and the clinical performance of the polyethylene component continues to be warranted with unicondylar knee arthroplasty implants.
authors.affiliation: Anderson Orthopaedic Research Institute, P.O. Box 7088, Alexandria, VA 22307, USA. collier@aori.org
authors.forename: Matthew B
authors.initials: MB
authors.lastname: Collier
authors.forename: C Anderson
authors.initials: CA
authors.lastname: Engh
authors.forename: Gerard A
authors.initials: GA
authors.lastname: Engh
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000295:instrumentation; D001672:Biocompatible Materials / Q000009:adverse effects*; D005260:Female; D006801:Humans; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D020959:Polyethylene / Q000009:adverse effects*; D011475:Prosthesis Failure; D012189:Retrospective Studies; D013997:Time Factors; D016896:Treatment Outcome
chemical_list: D001672:Biocompatible Materials; D020959:Polyethylene