Surgeon removing the damaged bone and cartilage from the knee of an 86-year-old male patient with osteoarthritis for total knee replacement surgery. Osteoarthritis is the most common form of arthritis (inflammation and swelling of the joints). It occurs when the cartilage at the end of the bone breaks down, causing pain and swelling. Total knee replacement surgery is a procedure that involves removing the damaged ends of the femur (thighbone) and tibia (shinbone) and replacing them with metal or plastic prosthesis. This allows the joints to move more smoothly across each other, reducing pain and improving functionality.