The optimal surgical procedure for the arthritic knee depends upon the type of arthritis and the patient. If the patient is 'high demand' (i.e., relatively active and young), and has incongruous arthritis (in either the medial or lateral compartments but not both), then realignment by osteotomy transfers the weight to the healthy compartment. If the osteotomy is successful, the patient may continue a physically demanding lifestyle. Knee replacement is indicated if the patient is 'low demand' (i.e., elderly or suffering from multiple joint disease) and has congruous arthritis, with destruction of both weight-bearing compartments. Knee replacement does not allow the same activity level as realignment but, fortunately, the low demand patient tends to have congruous disease (e.g., rheumatoid arthritis) and the high demand patient incongruous disease (e.g., osteoarthritis).