Can Microcomputed Tomography Measure Retrieved Polyethylene Wear? Comparing Fixed-bearing and Rotating-platform Knees

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 mm 3 . The average wear rate was 58 ± 41 mm 3 /year. Wear was 69% of penetration, demonstrating the contribution of deformation to knee wear. Rotating-platform wear rate was 43 ± 25 mm 3 /year and the fixed-bearing rate was 74 ± 49 mm 3 /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.

Relationship of surface damage appearance and volumetric wear in retrieved TKR polyethylene liners

“…Individual wear rates can then be adjusted by the population creep. Other retrieval studies measuring volumetric wear on the articular surface have calculated wear rates ranging from 17.3 to 749 mm 3 /year . Many of these studies are limited by low measurement resolution, accuracy of reference surface, or inclusion of severely delaminated components.…”

“…Other retrieval studies measuring volumetric wear on the articular surface have calculated wear rates ranging from 17.3 to 749 mm 3 /year. 11,13,14,16,25,26 Many of these studies are limited by low measurement resolution, accuracy of reference surface, or inclusion of severely delaminated components. Notably, the wear rate closest to our finding was also calculated as the slope of the linear regression for the entire population with consideration for volume lost to creep, 14 whereas the others were derived as a mean rate of wear volumes normalized to time in situ-measurements that inherently include plastic deformation.…”

How Does Wear Rate Compare in Well-functioning Total Hip and Knee Replacements? A Postmortem Polyethylene Liner Study

“…Other than the study by Knowlton and Wimmer [19], we are aware of only one other study reporting measured volumetric liner wear in retrieved TKRs [8], and it is for contemporary prosthesis designs (LCS 1 , P.F.C. 1 Sigma 1 , Sigma 1 Rotating Platform; DePuy-Synthes, West Chester, PA, USA) ( Table 3).…”

Peripheral snap-fit locking mechanisms and smooth surface finish of tibial trays reduce backside wear in fixed-bearing total knee arthroplasty

“…2013, Engh et al. 2013). Due to this limitation, we examined the retrievals using SEM, to determine how damage of each type corresponds to wear mechanisms responsible for the release of polyethylene particles.…”