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

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 (μCT) 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 < 20mm³ per 10⁶ cycles. The aim of this study was to compare μCT volume measurements with gravimetric measurements and to assess whether μCT can quantify wear volumes of n-vitro tested TDRs. μCT 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 ±3mm^;3, at least three orders of magnitude greater than those determined for gravimetric measurements. In conclusion, the μCT 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/i> data. It is best used alongside gravimetric measurements to maintain the high level of precision that these measurements provide.