Precision and sources of variability in the assessment of rheumatoid arthritis erosions by HRpQCT

Abstract Objectives To assess the precision and the sources of variation due to repositioning of the manual measurement of erosions located on the metacarpophalangeal joints (MCP) with High-Resolution peripheral Quantitative Computed Tomography (HRpQCT) in rheumatoid arthritis (RA). Methods RA patients with at least one erosion on the 2nd, 3rd or 4th MCP on conventional radiographs were included. Two scans were performed the same day with repositioning. The main outcome was to calculate the short-term precision of the width, depth, and volume of erosions. Secondary outcomes were intra-operator and inter-operator precision, the least significant change, and the sources of variability of the measurement. Results Twenty-nine patients were included, allowing analysis of 406 erosions from 0.9 to 3 mm of diameter. Intraclass correlation coefficients (ICC) for the precision of the measurement of the axial width, axial depth, and volume after repositioning were 0.80, 0.96, and 0.99, respectively. RMS CV and RMS SD were 16%, 0.26 mm; 17.5%, 0.32 mm; and 19.7%, 0.93 mm 3 , respectively. For intra-operator precision, ICCs were 0.92, 0.97, and 0.99 with RMS CV of 16%, 16.4%, and 18.7%, respectively. Inter-operator precision of the volume was 0.99 with RMS CV of 14%. Least significant change of width, depth, and volume were 0.3 mm, 0.2 mm, and 0.3 mm 3 . There was no significant correlation with bone microarchitecture parameters. Conclusion HRpQCT analysis is a reproducible method to characterize and measure erosions, without effect of the repositioning. However, we showed weak precision in manual measurement due to intra-operator variability.