The articular cartilage is relatively resistant to this degradation whereas the bone on the margins of the joint adjacent to the cartilage is not resistant. Similar erosions can be seen in psoriatic arthritis and Reiter's syndrome. Because the articular cartilage is preserved until late in disease in inflammatory arthritides, the width of the joint space is also preserved until late in disease, unlike osteoarthritis. As rheumatoid arthritis progresses, there is progressive joint destruction with collapse of the joint space. In some instances, the joint will fuse in an attempt by the bone to heal itself.
Joint fusion is more common in psoriatic arthritis.
As a result of the inflammatory process in the joints of RA, there is increased blood flow to the region of bone surrounding the joint. This increased blood flow results in increased resorption of bone and produces a periarticular osteopenia which is detectable radiographically. Similar deformities of the hand can be seen in SLE and Jaccoud's arthropathy. These arthopathies are distinguished from RA by the absence of destructive changes in the joints such as marginal erosions. In the hands, RA has a characteristic distribution of disease with predominant involvement of the carpal and carpometacarpal joints, with erosions and destruction of these joints.