OA is a disease of the whole joint, which includes: cartilage bone ligaments fat pads lining of the joint, called the synovium In OA, cartilage breaks down, which results in changes to the bone and joint tissues. Alongside inflammation, this can cause pain, stiffness, and loss of flexibility.

Osteoarthritis occurs when the cartilage that cushions the ends of bones in your joints gradually deteriorates. Cartilage is a firm, slippery tissue that enables nearly frictionless joint motion. Eventually, if the cartilage wears down completely, bone will rub on bone. Osteoarthritis has often been referred to as a wear and tear disease.

Osteoarthritis starts with the breakdown of cartilage in the joint. As the cartilage wears down, the bone ends may thicken and form bony growths (spurs). Bone spurs interfere with joint movement. Bits of bone and cartilage may float in the joint space. Fluid-filled cysts may form in the bone and limit joint movement.

The pathogenesis of OA involves a degradation of cartilage and remodelling of bone due to an active response of chondrocytes in the articular cartilage and the inflammatory cells in the surrounding tissues. The release of enzymes from these cells break down collagen and proteoglycans, destroying the articular cartilage.