AI-Derived Carpal Compactness Metrics as Quantitative Imaging Measures of Global Carpal Architecture in Early Rheumatoid Arthritis

Rheumatoid arthritis (RA) frequently involves the wrist joints, where early inflammation may induce subtle changes in carpal spatial architecture. This study investigated whether baseline (BL) ultrasound inflammation is associated with longitudinal changes in AI-derived compactness metrics and whether these metrics provide information complementary to conventional wrist radiographic scores. This study included 159 patients with early RA who underwent BL and follow-up (FU) bilateral wrist radiography and BL wrist ultrasound. Four AI-derived centroid-based compactness metrics—root-mean-square-radius (RMSR), mean pairwise distance (MPD), median radius (R50), and 90th-percentile-radius (R90)—were calculated, and their annualized changes were evaluated in relation to conventional wrist SvdH scores and BL ultrasound inflammation, including gray-scale (GS), power Doppler (PD), GS+PD, and vascularity percentage (VS%). Associations were assessed using correlation and subgroup analyses. AI-derived compactness metrics at BL and FU, as well as their annualized changes, were not significantly associated with conventional wrist radiographic scores. In contrast, BL ultrasound inflammation was significantly associated with subsequent increases in compactness metrics. BL GS, PD, and GS+PD scores showed significant positive correlations with annualized changes in RMSR, MPD, R50, and R90 (r = 0.18–0.25, p < 0.05). Subgroup analyses similarly demonstrated greater increases in compactness metrics in patients with positive GS or PD activity. Annualized changes in AI-derived compactness metrics were associated with baseline ultrasound inflammation but not with changes in conventional wrist radiographic scores. These findings suggest that AI-derived compactness metrics may provide complementary quantitative information on global carpal spatial architecture in early RA.