Abstract
Background
Wear of total knee polyethylene has been quantified gravimetrically with thickness measurements and evaluation of surface wear modes. However, these techniques do not localize volumetric wear.
Questions/Purposes
We used micro-CT scans of retrieved total knee liners and unworn, new liners to determine the volume and location of wear.
Methods
We retrieved 12 fixed and 12 rotating-platform bearings after a mean 52 months of use. Inserts were weighed and thickness was measured. Micro-CT scans of retrieved and matched new liners were superimposed to compare the location and magnitude of wear.
Results
The average total wear was 254 ± 248 mm3. The average wear rate was 58 ± 41 mm3/year. Wear was 69% of penetration, demonstrating the contribution of deformation to knee wear. Rotating-platform wear rate was 43 ± 25 mm3/year and the fixed-bearing rate was 74 ± 49 mm3/year. Five percent of the rotating-platform wear rate came from the backside compared with 14% of the fixed-bearing wear rate.
Conclusions
Micro-CT can determine the volume and location of wear of retrieved tibial liners. Because the magnitude of the manufacturing tolerances was approximately half the magnitude of the total wear on average, accounting for the potential influence of tolerances is important to accurately measure volumetric wear if the unworn (preimplantation) geometry of the insert is unknown. Without accounting for tolerances, this technique may not be applicable for retrievals with a short followup that have low wear. However, application of micro-CT could be of value in determining the exact location of wear in knee simulator studies in which the same insert is measured repeatedly and manufacturing tolerances are not a concern.
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Acknowledgments
We thank DePuy Orthopaedics, a Johnson & Johnson company (Warsaw, IN, USA), for providing the control inserts used for this study.
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One author (CAE) certifies that he has or may receive payments or benefits, in any one year, an amount in excess of $100,000, from DePuy, a Johnson & Johnson company (Warsaw, IN, USA), related to this work. The institution (AORI) of the authors (CAE, RLZ, RHH, GAE) has received funding to support this research from DePuy, a Johnson & Johnson company, and Inova Health Services.
All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research editors and board members are on file with the publication and can be viewed on request.
Each author certifies that his or her institution approved the human protocol for this investigation and that all investigations were conducted in conformity with ethical principles of research.
Clinical Orthopaedics and Related Research neither advocates nor endorses the use of any treatment, drug, or device. Readers are encouraged to always seek additional information, including FDA-approval status, of any drug or device prior to clinical use.
This work was performed at Anderson Orthopaedic Research Institute, Alexandria, VA, USA, and Inova Center for Joint Replacement at Mount Vernon Hospital, Alexandria, VA, USA.
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Engh, C.A., Zimmerman, R.L., Hopper, R.H. et al. Can Microcomputed Tomography Measure Retrieved Polyethylene Wear? Comparing Fixed-bearing and Rotating-platform Knees. Clin Orthop Relat Res 471, 86–93 (2013). https://doi.org/10.1007/s11999-012-2513-2
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DOI: https://doi.org/10.1007/s11999-012-2513-2