Contribution of the bone and cartilage/soft tissue components of the joint damage to the level of disability in rheumatoid arthritis patients: a longitudinal study

The study aims to analyze the association between the bone and cartilage/periarticular components of the radiographic joint damage and disability over the course of disease, in a cohort of rheumatoid arthritis (RA) patients from a day-to-day clinical practice. The secondary aim is to study the role of demographic and disease-related variables in this association. We performed a retrospective longitudinal study including 736 RA patients. Disability was assessed with the health assessment questionnaire (HAQ), and radiographic joint damage of hands and wrists with the Sharp van-der-Heijde score (total (SHS), erosion (ES), and narrowing/(sub)luxation (NSLS) components]. Generalized estimating equations models, adjusted by disease activity, demographic and disease-related variables, were used to test the relationship between SHS and medium-term (median value of the HAQs performed in the following year after each radiograph) and long-term (set of HAQ measures performed during follow-up, at least 1 year apart from the first x-ray) disability. Interaction terms between the SHS and demographic and disease-related variables were introduced in the models. To account for multiple testing, Bonferroni correction was applied. NSLS was independently associated with medium-term disability, even after Bonferroni correction. We observed significant and positive interactions between NSLS and age at x-ray, and with the ES. SHS showed no association with long-term disability. The cartilage/soft tissue component of the radiographic joint damage seems to exert a much more important role in medium-term disability than the erosive component. This association could be modulated by the age at the x-ray and by the magnitude of the erosive damage.