The fluid is secreted by a thin membrane, the synovial membrane, thalines the inside of the joint capsule. Thanks to this viscous fluid, and to the smooth, rubbery, blue-white cartilage that covers the ends of the bones, the bones within the joint normally glide smoothly past one another. In healthy joints, the synovial membrane is thin, the cartilage that covers the bones is smooth, and a thin layer of synovial fluid covers the bone surfaces. If anything goes wrong with any of these factors, arthritis can result. Arthritis may appear suddenly or come on gradually.
Some people feel a sharp burning or grinding pain.
Others compare the pain to that of a toothache. Moving the joint usually hurts, although sometimes there is only stiffness. The swelling and deformity that takes place in arthritic joints can result from a thickening of the synovial membrane, an increase in the secretion of synovial fluid, enlargement of the bones, or some combination of these factors. There are many different types of arthritis. Osteoarthritis involves deterioration of the cartilage that covers the ends of the bones.