After being informed about the study and potential risks, all patients giving written informed consent will be included in the study.~At baseline, before surgery, all patients will meet a nurse, a physical therapist, and an orthopedic doctor and answer questions about their health condition and do functional tests.~Each week is randomized to be either peanut ball or standard exercise week, with all patients during that week receiving the same treatment. Thus, depending on what week the patients are operated they will be mobilized with postoperative exercise with a peanut ball or to a standard exercise program (no peanut ball) 3-5 times/day for 6 weeks. All patients randomized to exercise with a peanut ball will receive a ball for free to bring home.~At the ward, the nurses will ask about the patient's pain level two times a day and register all medicines. The physical therapist will introduce the exercise and inform the patients to do the exercise 3-5 times/day a´ 15 minutes and fill in all exercises in an exercise diary.~2 weeks after surgery all patients have a standard visit to a nurse and a physical therapist at the orthopedic department. At this visit, the nurse will register the pain level and all intake of medicine and the physical therapist will measure the range of movement and the sit to stand test.~3 months after surgery all patients have a standard visit to a physical therapist at the orthopedic department. At this visit, all outcomes will be filled in or measured.
The purpose of this randomized controlled study is to evaluate the effect of postoperative exercise with a peanut ball after total knee replacement, on pain, intake of pain killers, knee function, and health-related quality of life.