What is the clinical relevance of erosions and joint space narrowing in RA?

The association between joint damage and disability in rheumatoid arthritis (RA), especially in the later stages of disease, is a main reason why radiographic joint damage is a common and valid outcome measure in RA clinical trials. Most studies have assessed the effect of global joint damage, which has limited our knowledge regarding the individual effects of erosions and cartilage damage on physical function. However, recent data have indicated that joint space narrowing is more closely related to functional status than erosions. Modern imaging techniques that provide improved assessment of the cartilage itself, instead of only joint space narrowing, might help disentangle the separate associations of erosive bone damage and cartilage damage with physical function in patients with RA. The aim of this article is to discuss the current knowledge within this field and the clinical consequences thereof.