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The Journal of Bone and Joint Surgery (American) 84:369-371 (2002)
© 2002 The Journal of Bone and Joint Surgery, Inc.

Scientific Article

Analysis of Polyethylene Thickness of Tibial Components in Total Knee Replacement

S. A. Edwards, FRCS, H. G. Pandit, FRCS(Orth), J. L. Ramos, MD, PhD, FRCS(Orth) and M. L. Grover, FRCS

Investigation performed at the Department of Orthopaedics, Queen Alexandra Hospital, Portsmouth, England

S.A. Edwards, FRCS
29 Valerian Avenue, Titchfield, Fareham, Hants P015 5TF, United Kingdom. E-mail address: stuart{at}eedwards.freeserve.co.uk

H.G. Pandit, FRCS(Orth)
J.L. Ramos, MD, PhD, FRCS(Orth)
M.L. Grover, FRCS
Department of Orthopaedics, Queen Alexandra Hospital, Cosham, Portsmouth PO6 3LY, England

No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.

Background: Excessive wear of the polyethylene bearing surfaces of tibial components has become an important factor in early failure of total knee arthroplasty. Inadequate thickness of the polyethylene insert is one cause of excessive wear, and various minimum thicknesses have been recommended in order to reduce contact stresses within the polyethylene. However, the true thicknesses of modular polyethylene tibial inserts typically are not stated accurately by the manufacturers in their product information. The purpose of this study was to determine whether the information about the thickness of tibial inserts supplied by the manufacturers is adequate.

Methods: Five of the thinnest available polyethylene tibial inserts from five different manufacturers were selected. The minimum thickness of each was measured with use of a Sigma electronic micrometer comparator to an accuracy of ±0.005 mm.

Results: The stated thicknesses of the polyethylene tibial inserts were 8, 9, and 10 mm, values that differed markedly from the actual minimum thicknesses, which ranged from 5.5722 to 6.2048 mm (mean values).

Conclusion: The thickness of polyethylene tibial inserts has been implicated as a potential cause of excessive wear and early failure of total knee replacements. This paper highlights the fact that the information supplied by the manufacturers is inaccurate and potentially misleading; in one case, the true thickness was much less than the recommended minimum thickness. We recommend that the minimum thickness of the tibial components as well as the combined thickness of the polyethylene insert and the metal tibial tray be specified in the product information and on the packaged insert.


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