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The Journal of Bone and Joint Surgery (American) 84:1849-1855 (2002)
© 2002 The Journal of Bone and Joint Surgery, Inc.

Scientific Article

Tibial Interface Wear in Retrieved Total Knee Components and Correlations with Modular Insert Motion

Anand R. Rao, BS, Gerard A. Engh, MD, Matthew B. Collier, MS and Smain Lounici, MS

Investigation performed at the Anderson Orthopaedic Research Institute, Alexandria, Virginia

Anand R. Rao, BS
Gerard A. Engh, MD
Matthew B. Collier, MS
Smain Lounici, MS
Anderson Orthopaedic Research Institute, c/o Rebecca Wolf, P.O. Box 7088, Alexandria, VA 22307

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.

Background: Wear occurring at the interface between the polyethylene insert and metal baseplate of a modular tibial component has become an increasingly common finding at the time of revision total knee arthroplasty. Although this so-called backside wear on retrieved polyethylene inserts has been evaluated in prior studies, wear on retrieved metal baseplates has not been described, to our knowledge. The purposes of the present study were to characterize backside wear on retrieved polyethylene inserts and on the mating surfaces of their corresponding baseplates and to investigate if there is a relationship between backside wear and relative motion of the modular elements.

Methods: Twenty-nine retrieved modular tibial components of twelve fixed-bearing designs were analyzed in vitro with regard to backside wear and relative motion between the polyethylene insert and the metal baseplate. We graded the backside of each polyethylene insert and the mating surface of the metal baseplate for wear with use of a scoring system that consisted of three modes of wear and three levels of severity of wear. Relative motion between the insert and the baseplate was measured in the transverse plane with use of a mechanical testing machine. These measurements were used to compute the insert motion index, which served to quantify unrestricted motion of the insert with respect to the baseplate.

Results: The mean insert motion index for the tibial components was 416 µm (range, 104 µm to 760 µm). On a wear-grading scale ranging from 0 to 54 (with 0 indicating no wear), the mean backside wear score was 30 (range, 12 to 48) for the inserts and 28 (range, 7 to 51) for the baseplates. Insert motion was positively correlated with backside polyethylene wear (p = 0.003) and baseplate wear (p < 0.001). Baseplate wear was strongly correlated with backside polyethylene wear (p < 0.001).

Conclusions: Backside wear was correlated with the relative motion between the polyethylene insert and the metal baseplate. New locking mechanism designs directed toward better methods of securing the polyethylene insert to the tibial tray are needed to minimize the generation of particulate wear debris at the modular interface.


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