Knee replacement is required when pain in the knee becomes unbearable caused by a number of factors. The most common reason is osteoarthritis. It is a degenerative disease where the cartilage which acts as a cushion between two bones involved in a synovial joint degenerate and cause the failure of the joint. This disease usually affects persons aged over 50 years and since it is degenerative, new tissue cannot be degenerated and eventually patient has to undergo knee replacement to restore normal quality of life. The other major reason is the development of rheumatoid arthritis. It is an autoimmune disease that targets the cartilage and leads to its destruction. Less common reasons include trauma to the knee and the subsequent injury to the cartilage, infective arthritis, psoriatic arthritis, etc. Knee replacement may be partial or total depending on the extent of damage to the joint.