Objectives To evaluate the separate effects of erosions (E) (bone damage), joint space narrowing (JSN) (cartilage loss) and (sub)luxation (SLUX) (soft tissue damage) in four different joint groups on physical disability in rheumatoid arthritis (RA).

Methods 3-year follow-up data from the Rheumatoid Arthritis PreventIon of structural Damage (RAPID) 1 and 2 trials were used. These randomised controlled trials compared certolizumab plus methotrexate (MTX) versus MTX in patients with RA. Physical function was measured by Health Assessment Questionnaire (HAQ). Radiographic damage was measured by the van der Heijde-modified Sharp score; separate scores for E, JSN and SLUX were available. Generalised estimating equations were performed to assess the relationship between HAQ and E, JSN and SLUX scores, separately and in all joint groups.

Results In separate models for each type of damage and after adjusting for age, gender, baseline disease activity and treatment group, E and JSN were more strongly associated with HAQ than with SLUX. In combined models, JSN was the only type of lesion associated with HAQ when all joints were included together. When separate joint groups were analysed, E in the wrist and JSN in the metacarpophalangeal joints (MCPs) were most strongly associated with function.

Conclusions Among RA-related joint damage, cartilage loss quantified by JSN is an important determinant of physical function. However, when analysing joint groups separately, erosive damage in the wrist and JSN in the MCPs had the most important influence on disability. These data indicate that the comprehensive assessment of joint damage is needed to reliably reflect disease-related damage.