Chronic degeneration, also known as degenerative joint disease, of the cartilage in the joint cavity leads to osteoarthritis, which primarily affects the knees, hips, hands, feet, and spine.
Cartilage provides a cushion between the bones at joint locations. As the cartilage wears down, bone may eventually rub against bone. When the cartilage deteriorates, the body attempts to repair the loss, often by creating new areas of bone along the edges of existing bone (bone spurs or osteophytes). Primary osteoarthritis is most common in the elderly. Secondary causes of osteoarthritis include repetitive stress injuries, trauma, chronic gout, and poor posture leading to misalignment of bones.
Rheumatoid arthritis is an autoimmune disease that causes chronic inflammation, deformity, and destruction of the joints. As synovial membranes become swollen and inflamed, the joint is infiltrated with white blood cells, which cause destruction to the articular cavity. The ligaments begin to erode which interferes with joint mobility. There are four stages of rheumatoid arthritis. 1) Inflammation of the synovial membrane leading to edema of the joint. 2) Pannus (thickened layers of granular tissue) accumulates in the joint, leading to thickening of the joint capsule. 3) Fibrous ankylosis (scar formation in the joint space) along with bone and muscle atrophy leads to deformity. 4) Calcification of the joint leading to total immobility.
There is not a known cause for rheumatoid arthritis. It is believed that there may be connections between genetics and the environment. It is considered a systemic disease because it causes inflammation in multiple other organs.