The accuracy and precision of a micro computer tomography volumetric measurement technique for the analysis of in-vitro tested total disc replacements

Abstract

Total disc replacements (TDRs) in the spine have been clinically successful in the short term, but there are concerns over long-term failure due to wear, as seen in other joint replacements. Simulators have been used to investigate the wear of TDRs, but only gravimetric measurements have been used to assess material loss. Micro computer tomography (microCT) has been used for volumetric measurement of explanted components but has yet to be used for in-vitro studies with the wear typically less than < 20 mm3 per 10(6) cycles. The aim of this study was to compare microCT volume measurements with gravimetric measurements and to assess whether microCT can quantify wear volumes of in-vitro tested TDRs. microCT measurements of TDR polyethylene cores were undertaken and the results compared with gravimetric assessments. The effects of repositioning, integration time, and scan resolution were investigated. The best volume measurement resolution was found to be +/- 3 mm3, at least three orders of magnitude greater than those determined for gravimetric measurements. In conclusion, the microCT measurement technique is suitable for quantifying in-vitro TDR polyethylene wear volumes and can provide qualitative data (e.g. wear location), and also further quantitative data (e.g. height loss), assisting comparisons with in-vivo and ex-vivo data. It is best used alongside gravimetric measurements to maintain the high level of precision that these measurements provide.

The Effect of Anterior-Posterior Shear on the Wear of CHARITÉ Total Disc Replacement

“…The fourteen discs were also scanned using a microCT scanner (Scanco µCT80, Scanco Medical, Busserdorf, Switzerland) using a resolution of 36µm with the use of a 1024 × 1024 plane image matrix, voltage of 70kVp and current of 114µA. The volume of each core was calculated using a segmentation method to separate polyethylene and air and then performing a simple voxel count [16]. …”

Regional Measurements of Surface Deviation Volume in Worn Polyethylene Joint Replacement Components

“…The intra-observer and inter-observer variability reported here compares well to other wear volume measurement techniques, which have been primarily applied to components from total hip replacement. Bowden et al [3] used micro-CT to measure the wear volume in retrieved acetabular liners. They reported intra-observer and interobserver variability of approximately 10%, with the variability increasing to 50% for one liner with a low volume of wear.…”

“…A number of in vitro laboratory tools have been developed to quantify the gravimetric or volumetric changes (due to wear) in polyethylene components that have been retrieved from patients or undergone wear simulator testing. Recently, micro-computed tomography (micro-CT) has been used to measure the overall volume of polyethylene tibial inserts, acetabular liners, and spinal discs [1][2][3], and to measure the volume loss due to wear in retrieved polyethylene acetabular liners [4]. Techniques have also been developed to measure and map the three-dimensional surface deviations due to wear in tibial inserts and acetabular liners [1][2].…”

Highly cross-linked polyethylene acetabular liners retrieved four to five years after revision surgery: A report of two cases

“…Although micro-CT has been demonstrated to be accurate and highly repeatable for quantification of volumetric wear in retrieved polyethylene acetabular liners, scanner error up to 0.6% has been reported (Bowden et al, 2005). Vicars et al (2009) reported a volume measurement resolution of ±3 mm 3 for micro-CT of the polyethylene cores from total disc replacements, and recommended that gravimetric analysis should be used alongside micro-CT to ensure accuracy. We observed an excellent agreement between micro-CT and gravimetric volumes in this study, to a mean difference of 0.42%.…”

“…The liners were scanned with micro-computed tomography (micro-CT) and underwent 3D surface analysis using a previously described approach (Teeter et al, 2010;Vicars et al, 2009;Bowden et al, 2005). A new, never-implanted liner of the same type as the retrieved liner (Reflection, Smith and Nephew, Memphis, TN; 20 degree overhang, size H, 32 mm inner diameter, 62-64 outer diameter) was also scanned to serve as an unworn reference for the surface analysis.…”