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Shelf Age of the Polyethylene Tibial Component and Outcome of Unicondylar Knee Arthroplasty
Matthew B. Collier, MS1; C. Anderson EnghJr., MD1; Gerard A. Engh, MD1
1 Anderson Orthopaedic Research Institute, P.O. Box 7088, Alexandria, VA 22307. E-mail address for M.B. Collier: collier@aori.org
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The authors did not receive grants or outside funding in support of their research or preparation of this manuscript. They did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. A commercial entity (INOVA Health Care Services, Falls Church, Virginia) paid or directed, or agreed to pay or direct, benefits to a research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.
Investigation performed at the Anderson Orthopaedic Research Institute, Alexandria, Virginia

The Journal of Bone and Joint Surgery, Incorporated
J Bone Joint Surg Am, 2004 Apr 01;86(4):763-769
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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.

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

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    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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