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
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.
Level of Evidence: Therapeutic study, Level III-2
(retrospective cohort study). See Instructions to Authors for a complete
description of levels of evidence.