OA most commonly affects middle-aged and elderly people, and can range from mild to very severe. It typically affects hands and weight-bearing joints, such as the knees, hips, back, and feet. The exact causes of OA are unknown. It is characterized by the inflammation of the membrane lining the joints, which causes swelling, pain, stiffness, redness and warmth in the joint. The inflamed joint lining, the synovium, invades and damages bone and cartilage.
Inflammatory cells release an enzyme that gradually destroys bone and cartilage.
The joint loses its shape and alignment, resulting in pain, loss of movement, and eventually complete destruction of the joint. RA usually begins in middle age, but can occur at any age. The cause of RA is unknown, but it is know to be an autoimmune disease, meaning that the body's immune system malfunctions and attacks healthy tissue.