Rapid Polyethylene Failure of Unicondylar Tibial Components Sterilized with Gamma Irradiation in Air and Implanted After a Long Shelf Life
Thomas F. McGovern, MD, Deborah J. Ammeen, BS, John P. Collier, DE, Barbara H. Currier, MChE and Gerard A. Engh, MD
Investigation performed at Anderson Orthopaedic Research Institute, Alexandria, Virginia
Background: The mechanical toughness of polyethylene that has been sterilized by gamma irradiation in air decreases after a long shelf life. The purpose of the present study is to report the high failure rate after unicondylar knee replacements performed with polyethylene bearings that had been sterilized with gamma irradiation in air and implanted after a shelf life of 4.4 years.
Methods: Between December 1997 and January 2000, seventy-five unicondylar knee replacements were performed in sixty-two patients. All patients were followed both clinically and radiographically. A revision operation was offered when the patient had pain, swelling, and radiographic evidence of rapid polyethylene wear. The effect of aging of the polyethylene during storage was evaluated by dividing the knees into three groups on the basis of shelf life and comparing them with regard to the rate of revision and the observed wear of the polyethylene. Four retrieved components were examined for the presence of oxidation.
Results: At a mean of eighteen months after the arthroplasty, thirty knees had been revised and seven were scheduled for revision. The rate of polyethylene wear increased as the shelf life increased. There was a significant inverse linear correlation between the shelf life of the polyethylene and the time to revision (p < 0.01, r 2 = 0.64). All retrieved components had greater-than-expected wear with pitting and delamination of the surface. Seven components had fractured, and ten had both fractured and fragmented. Analysis of four components confirmed severe oxidation of the polyethylene.
Conclusion: The present study demonstrated early, severe wear of tibial polyethylene bearings that had been sterilized by gamma irradiation in air and stored for 4.4 years. This risk can be minimized by ensuring that implants have not been sterilized with gamma irradiation in air and stored for several years.
Author Information:
E-mail address for T.F. McGovern, D.J. Ammeen, and G.A. Engh: ammeen@aori.org
Thomas
F. McGovern, MD, Deborah J. Ammeen, BS, Gerard A. Engh, MD
Anderson Orthopaedic
Research Institute, 2501 Parker's Lane, Suite 200, Alexandria, VA 22306.
John
P. Collier and DE Barbara H. Currier, MChE
Thayer School of Engineering, Dartmouth College
8000 Cummings Hall
Hanover, NH 03755
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. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.