Validation of Combined Indicator Using Joint Index Vector and Pain Score for Risk Weight Calculation of Incident Bone Fragility Fracture in Patients with Rheumatoid Arthritis

Background: Risk factors, including Joint Index Vector (JIV), a new disease activity indicator based on three-axis coordinates, and a pain score using a visual analog scale (PS-VAS), were evaluated for incident bone fragility fractures (inc-BFF) in patients with rheumatoid arthritis (RA) in a retrospective case–control study. Methods: RA patients who were followed for at least two consecutive years (RA) and a control group consisting of patients without RA but with similar background demographics (non-RA) were recruited and monitored. The prevalence of inc-BFF was compared between the two groups. Common potential risk factors in both groups and RA-specific factors within the RA group regarding inc-BFF were analyzed statistically. Results: A total of 278 patients were studied in each group. There was no significant difference in the prevalence of inc-BFF between the two groups. Presenting RA was not a major factor in developing inc-BFF. Higher Vz in the JIV, which reflects the difference in the involvement ratio between large and small joints, and higher PS-VAS showed significantly higher hazard ratios in a univariate model. Vz > 0.01, PS-VAS ≥ 25.5, and simplified disease activity index ≥ 2.11 at follow-up, along with PS-VAS at baseline > 21.0, are the key cutoff indices for RA-specific risk factors. When two of these factors were combined, the combination of Vz and PS-VAS at follow-up resulted in the highest hazard ratio (4.25; p < 0.001). Conclusions: These results suggest that combining Vz and PS-VAS is the key risk indicator for inc-BFF.