 Total knee arthroplasty TKA is increasingly common in the treatment of osteoarthrosis. Despite aggressive analgesic regimes, TKA is associated with moderate to severe postoperative pain, delaying mobilization and hospital discharge. A relatively new method for controlling postoperative pain after TKA is local infiltration analgesia LIA which consists of local infiltration with Ropivacaine and adrenaline.3 studies haved showed promising results of LIA, but none have documented a superior analgesic effect versus placebo.Patients receiving bilateral knee arthroplasty are recruited to receive LIA and placebo infiltration.The aim of the study is to demonstrate an analgesic effect of LIA versus placebo. 