Physical disability in rheumatoid arthritis is associated with cartilage damage rather than bone destruction

Background Joint destruction in rheumatoid arthritis is comprised of cartilage and bone damage, which can be evaluated radiographically separately by the joint space narrowing (JSN) and erosion (ERO) scores. It is currently unclear to which extent these components affect irreversible functional disability. The aim of the present work was to determine these contributions. Methods Data, kindly provided by the sponsors, was evaluated from several randomised controlled clinical trials on adalimumab, etanercept, infliximab and leflunomide. Patients who reached stringent remission according to the Simplified Disease Activity Index (SDAI <= 3.3) were extracted to eliminate the activity related (ie, reversible) component of disability. In these patients, residual Health Assessment Questionnaire Disability Index (HAQ-DI) score at the time of remission (to reflect the level of 'irreversible' disability) was determined and related to baseline measures of ERO and JSN scores univariately, by stratification and in adjusted regression models. Results A total of 748 patients who achieved a state of remission were analysed (16.3% of the total pooled population of 4602 patients). In the univariate analyses, mean residual HAQ-DI values in remission were significantly larger in higher tertiles of JSN and ERO (ERO: 0.21, 0.25, 0.35; JSN: 0.19, 0.24, 0.39; p < 0.001 for both). In stratified analyses, mean residual HAQ-DI scores were larger in higher tertiles of JSN within the first tertile of ERO (0.18, 0.25, 0.29; p=0.05), as well as the second (0.21, 0.24, 0.29; p=0.19) and the third (0.12, 0.23, 0.42; p < 0.001). In contrast, there was no such trend across ERO tertiles within the first JSN tertile (0.18, 0.21, 0.12; p=0.99) and the second tertile (0.25, 0.24, 0.23; p=0.77), and only marginally within the third tertile of JSN (0.29, 0.29, 0.42; p=0.07). Adjusted multivariate regression models supported the significant association of JSN on residual disability. Conclusions Cartilage damage appears to be the more clearly associated with irreversible physical disability than bony damage. These data suggest that particular attention should be given to therapeutic interference with cartilage destruction.