Which feature is typical in rheumatoid arthritis observed on X-rays?

The characteristic narrowing of joint space observed in rheumatoid arthritis (RA) on X-rays is primarily due to synovial inflammation and subsequent erosion of the cartilage. As the disease progresses, the inflammatory processes lead to the destruction of cartilage and bone, which reduces the space within the joint.

This narrowing is a key feature that differentiates RA from other types of arthritis, such as osteoarthritis, where joint space narrowing can also occur but is typically accompanied by osteophyte formation rather than the erosive changes seen in RA. Additionally, joint space narrowing can be an early indicator of the disease, often visible before other more significant structural changes take place.

Other radiological features of RA, although relevant, do not reflect the primary nature of the disease as directly as joint space narrowing. For instance, subchondral sclerosing is often seen in osteoarthritis rather than being prominent in RA, and bone fusion (ankylosis) is more characteristic of conditions like ankylosing spondylitis. Joint hypermobility usually indicates laxity and is not intrinsic to the destructive processes of RA. Thus, the observation of joint space narrowing is a definitive marker of the pathophysiological changes that occur in rheumatoid arthritis.