Inflammation is commonly associated with rheumatoid arthritis, psoriatic arthritis, and other types of inflammatory arthritis. On the other hand, osteoarthritis, is usually explained as "wear-and-tear" arthritis, meaning that it is related to aging and changes in the cartilage. But is it also tied to inflammation?
The short answer is: possibly. Osteoarthritis, also known as degenerative joint disease, is caused by the breakdown of articular cartilage -- the type of cartilage that covers the ends of bones in a joint. Over time, most older adults will develop some form of painful osteoarthritis (OA) in a joint or joints, such as the knees, hips, spine, or hand. While pain is common in OA, inflammation -- redness and swelling -- is usually associated with other types of arthritis.
However, as osteoarthritis progresses, inflammation can occur around an affected joint. It was thought that the inflammation is caused by cartilage fragments that break off and irritate the synovium (the smooth lining of a joint). However, MRIs taken during the early stages of osteoarthritis sometimes detect synovitis (inflammation of joint lining) even though the joint cartilage still appears normal. This indicates that other joint structures also may be involved in triggering inflammation.
There have been recent studies of inflammation in spinal arthritis that pointed to the entheses (the sites where ligaments or tendons attach to bone) as a potential location of joint inflammation in OA. Professors from Cardiff University in Wales and the University of Leeds in Great Britain investigated how entheses contribute to inflammation by studying dozens of ligament and tendon attachment samples from cadavers. They concluded that the mechanics of entheses may play a role in synovial inflammation in osteoarthritis as well as inflammatory types of arthritis.
"Histopathologic Changes at 'Synovio-Entheseal Complexes' Suggesting a Novel Mechanism for Synovitis in Osteoarthritis and Spondylarthritis". Michael Benjamin and Dennis McGonagle. Arthritis & Rheumatism. November 2007.