Inflammation as an important feature of osteoarthritis.

George Ehrlich’s paper “Osteoarthritis beginning with inflammation: definitions and correlations” emphasized the importance of inflammation as a component of osteoarthritis (1). In this paper, published over 25 years ago, Ehrlich described a cohort of predominantly menopausal females who presented with a deforming and inflammatory osteoarthritis, some of whom went on to develop changes characteristic of rheumatoid arthritis. Although the majority of patients were controlled with standard anti-inflammatory medications, a minority of the cohort suffered exacerbations of their disease and developed more extensive evidence of inflammation, including a positive rheumatoid factor. These patients presented initially with primarily interphalangeal involvement with clinical features of pain and inflammation. Large joints such as the shoulder and knee were also involved. Ehrlich raised the issue that this particular syndrome might be at the “interface” between osteoarthritis and rheumatoid arthritis, and inflammation is now well accepted as a feature of osteoarthritis. A current working definition of osteoarthritis maintains that it is a condition of synovial joints characterized by cartilage loss and evidence of accompanying periarticular bone response. Examination of synovial tissues from patients with osteoarthritis clearly shows evidence of inflammation, though this is not as aggressive as that seen in the inflammatory arthropathies such as rheumatoid arthritis. A key feature of osteoarthritis is the cartilage loss and the accompanying periarticular bone response which leads to the development of osteophytes and subchondral sclerosis. This is also accompanied by a degree of synovitis. With ageing of the population, the importance of osteoarthritis as a cause of disability is increasing in both industrialized countries and the developing world.