Computer-based methods to measure radiographic joint space width (JSW) have the potential to improve the longitudinal assessment of rheumatoid arthritis (RA). The purpose of this report was to measure the long-term patient repositioning reproducibility of software-measured radiographic JSW.
Patients underwent baseline and followup hand radiography examinations with a followup time of ≤3 years. To eliminate any JSW change due to real disease progression, the evaluation was performed on "unaffected" joints, defined as having JSW and erosion Sharp scores of 0 at both baseline and followup. The root mean square SD (RMSSD) and coefficient of variation (CV) were used as the reproducibility metrics.
The RMSSD was 0.14 mm (CV 10.5%) for all joints, 0.18 mm (CV 10.9%) for the metacarpophalangeal (MCP) joints, and 0.08 mm (CV 8.3%) for the proximal interphalangeal (PIP) joints. The distribution of JSW change was asymmetric, suggesting that narrowing due to RA progression occurred for several joints. A second analysis was performed, excluding joints where the loss of JSW was greater than 3 SDs. For this analysis, the RMSSD was 0.10 mm (CV 7.5%) for all joints, 0.12 mm (CV 7.3%) for the MCP joints, and 0.07 mm (CV 7.1%) for the PIP joints.
Repositioning reproducibility is very good but is likely to be a dominating factor compared to reader and software reproducibility. Additionally, further evidence is given that a software method is able to detect changes in some joints for which the Sharp score is insensitive.