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Clinical Results of Modular Polyethylene Insert Exchange with Retention of Total Knee Arthroplasty Components
Gerard A. Engh, M.D., Lisa M. Koralewicz, M.P.H., Thomas R. Pereles, M.D.
Modular polyethylene inserts have enabled surgeons to perform isolated tibial insert exchange while retaining well-fixed components. This study reviews results of insert revision and clarifies the role of this option versus complete revision of the total knee arthroplasty.
The senior author managed fifty-six patients (sixty-three knees) by revising the tibial polyethylene insert and retaining well-aligned and stable femoral and tibial components. Implants were in situ a mean fifty-nine months (range, two months to 108 months) at the time of insert revision with no implant in situ for more than nine years. Inserts removed at exchange were graded for wear of the articular surface, using the Hood classification system, and for undersurface wear using the method described by Wasielewski et al. Forty-eight knees were followed a mean 7.1 years (range, 2.6 years to 11.8 years) after insert revision. Knees that did not require additional surgery were considered successful.
Seven of forty-eight knees failed insert exchange due to accelerated wear of the new insert an average of fifty-four months after exchange. All of these required complete revision of all components. Inserts that replaced inserts revised for severe wear on pre-revision radiographs had a 27 percent failure rate (6/22) in less than five years. Thus, knees that had inserts initially exchanged for advanced wear were more likely to fail again (p < 0.05). Additionally, inserts that failed exchange had higher delamination scores (Hood) than inserts that did not fail (p < 0.05). All failed inserts had substantial backside wear. Metallosis (thirty knees) and osteolysis (nineteen knees) at revision were unrelated to exchange failure.
A simple revision of the tibial polyethylene insert should not be used to manage total knees that have accelerated polyethylene insert wear with delamination and grade three or four subsurface wear in less than ten years. Because a variety of patient, implant, and technical factors influence polyethylene wear, orthopaedists must consider multiple variables whenever contemplating a limited revision.
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