AB1130 RELIABILITY OF ULTRASOUND MEASUREMENT OF HYALINE CARTILAGE THICKNESS IN RHEUAMTOID ARTHRITIS

Abstract

Background Only few studies investigated the role of ultrasound (US) in the assessment of hyaline cartilage in rheumatoid arthritis (RA). Recently, a positive correlation was found between the US measurement of the metacarpal head cartilage thickness (MCT) and both the anatomical MCT and the radiographic joint space width1. Objectives To evaluate inter- and intra-observer reliability in the assessment of MCT in RA patients and healthy subjects; to compare the agreement of the sonographers in the assessment of the MCT using different methods (i.e. semiquantitative and quantitative); to determine the inter-observer smallest detectable difference (SDD) of MCT measured by US. Methods US assessment was performed by two rheumatologists on 160 metacarpophalangeal (MCP) joints of 10 healthy subjects and 10 patients with RA (according to 2010 ACR/EULAR classification criteria) using a MyLab Twice (Esaote Biomedica, Genoa, Italy) equipped with a linear very high frequency probe (i.e. 10-22 MHz) To assess inter-observer reliability, the hyaline cartilage of metacarpal head from II to V digits of both hands were examined independently on the same day by two rheumatologists (an experienced musculoskeletal sonographer and an investigator with limited US training). To assess intra-observer reliability, all the subjects were re-scanned using the same scanning protocol and the same US setting by one sonographer after a week. Hands were scanned with the MCP joints in maximal flexion (approximately 90°). The hyaline cartilage of all the metacarpal heads was scanned in longitudinal and transverse views in the central portion of the metacarpal head. Particular attention was paid on maintaining the probe in a position providing an angle of 90° between the direction of the US beam and the cartilage surface2. MCT was scored both semi-quantitatively (using a five-grade scoring system3) and quantitatively (using the average value of the longitudinal and transverse measures). The inter- and intra-observer agreements for assessing the MCT with the semiquantitative scoring system were calculated using Cohen’s kappa and interpreted according to Landis and Koch. The inter- and intra-observer agreements for assessing the MCT with the quantitative scoring system were calculated using intraclass correlation coefficients (ICC) and their 95% confident intervals (95%CI). The SDD was determined using Bland-Altman 95% limits of agreement method. Results The inter- and intra-observer agreements for the semiquantitative assessment of the MCT were moderate [k=0.59 (95%CI 0.35-0.83) and k=0.63 (95%CI 0.39-0.87), respectively]. Considering all the measurements, a substantial inter-observer [ICC= 0.88 (95%CI 0.82-0.92)] and intra-observer [ICC= 0.88 (95%CI 0.87-0.94)] agreements for the quantitative assessment of MCT were found. The SDD of the MCT measurement was: 0.11 mm for both longitudinal and transverse scans and 0.09 mm for the average of the two measures. Conclusion This study provides evidence in favor of the reliability of semiquantitative and quantitative US methods for assessing MCT in RA. Further studies are required to determine standard reference values of MCT by US in healthy subjects.