 200 patients with osteoarthritis OA of the knee necessitating total knee arthroplasty are entered into the study. All patients are given a standard protocol of analgesics pre- and postoperatively. All patients get periarticular LIA-injection 150 ml with a total of 300 mg Ropivacaine, 30 mg Toradol and 0.5 mg Adrenalin. In the end of the operation all patients get an epidural type of catheter intraarticular with a coupled continuous infusion pump that delivers 2 ml per hour and are disconnected after 48 hours. The University hospital pharmacy has prepared 200 pumps; 100 Active substance pumps with 100 ml Ropivacaine 10mgml and 100 placebo pumps with 100 ml sodium chloride NaCl. All patients are by computer software randomized to receive either active or placebo pump. Only one nurse, not involved in neither the operation nor the after treatment, has the key to what substance it is in the numbered pumps. Thus, it is a double blinded trial during the whole follow up period. Before the operation the patients are asked to fill out a knee specific outcome questionnaire, the Knee injury and Osteoarthritis Outcome Score KOOS, and a general outcome questionnaire, the Euroqol EQ-5D, and the knee range of motion is measured by a physiotherapist. After the operation the patients are monitored at the ward by the nurses and physiotherapists. The level of pain is measured twice daily noon and 8 PM according to the Visual-Analog-Scale VAS. The range of motion and is measured on day 4 and at the day 14 and day 30 follow up. The number of days the patients need to stay in hospital after operation are registered. The amount of extra doses of analgesics the patient requires are registered as well as the complications illness, wound problems, infections etc. The patients are to be followed clinically for 2 years as well as with outcome questionnaires. 