Illustration of osteoarthritis and arthritis of the knee. On the left, osteoarthritis of the knee showing meniscal deterioration, going as far as a deterioration of the bone surface on the contact surfaces of the joint. On the right, arthritis of the knee, showing joint inflammation, swelling of the synovial membrane, pain and burning. Enzymes are secreted in the synovial fluid that can destroy the cartilage and bone surface in the long run. (Photo by: BSIP/UIG via Getty Images)