In vitro quantification of wear in tibial inserts using microcomputed tomography

Abstract

Background: Wear of polyethylene tibial inserts can decrease the longevity of total knee arthroplasty. Wear is currently assessed using laboratory methods that may not permit backside wear measurements or do not quantify surface deviation.

Questions/purposes: We developed and validated a technique to quantify polyethylene wear in tibial inserts using microcomputed tomography (micro-CT), a nondestructive high-resolution imaging technique that provides detailed images of surface geometry in addition to volumetric measurements.

Methods: Six unworn and six wear-simulated polyethylene tibial inserts were evaluated. Each insert was scanned three times using micro-CT at a resolution of 50 μm. The insert surface was reconstructed for each scan and the insert volume was calculated. Gravimetric analysis was performed for all inserts, and the micro-CT and gravimetric volumes were compared to determine accuracy. We created three-dimensional surface deviation maps.

Results: Micro-CT generated high-quality three-dimensional renderings of the insert surface geometry. Between-scan precision was 0.07%; we observed no difference between micro-CT and gravimetric volume measurements.

Conclusions: Micro-CT can provide precise and accurate volumetric measurements in addition to quantifiable three-dimensional surface deviation maps for the entire insert surface. The technique has the potential to evaluate wear in wear simulator trials and retrieval studies.

Clinical relevance: This micro-CT technique combines the benefits of volumetric and surface scanning methods to quantify wear across all surfaces of polyethylene components with a single tool. When applied in wear simulator and retrieval studies, these measurements can be used to evaluate and predict the wear properties of the components.

Fig. 1A–B

(A) Photograph of inserts held in foam on the bed of the scanner and (B) a rendered image of the insert in the bed at a double-oblique angle of approximately 10° backward vertically and 3° laterally. The foam that held the inserts is radiotranslucent and does not appear in the reconstructed scan images.

Fig. 2A–B

Three-dimensional rendered volume images of an unworn tibial insert scanned with microcomputed tomography, including the (A) bearing surface and (B) backside. Note the “#3” and “10MM” embossed by the manufacturer in (A) (arrows).

Fig. 3A–B

(A) Rendered volume images of a worn tibial insert scanned with microcomputed tomography. (B) Worn areas are clearly visible on the bearing surfaces in both (A) (marked with arrows) and (B).

Fig. 4A–B

Mean volume of the six unworn inserts (UA through UF) as measured by (A) gravimetric analysis and microcomputed tomography (micro-CT) and (B) mean volume of the six worn inserts (WA through WF) as measured by gravimetric analysis and micro-CT. Bars are SD.

Fig. 5A–B

Surface deviation map for one of the six worn inserts versus an unworn insert for the (A) bearing surfaces and (B) backside. Measured deviations are in millimeters.