7)Scientific impact: There are many new and expensive instrumentations and implants on the market today. In order for Norwegian hospitals to be able to offer a high international standard of treatment, we need to evaluate carefully before choices are made. To date, computer navigation in knee replacement surgery is not well documented to be recommended as a standard procedure at all Norwegian hospitals. Earlier studies are lacking in that they have not reported an impact on long term implant survival. This study is unique by using RSA to predict long term outcome. It is also large enough to evaluate functional results and morbidity. In addition, the register analysis will give us information that has not been published. It is important for the patient to be confident that he/she receives the best treatment available, and it is important for the health care providers and funding authorities to receive clear and accurate information when choosing between two different treatments, in order to gain the most benefit.