The purpose of this study is to determine whether stopping Low Molecular Weight Heparin (LMWH) thromboprophylaxis is safe after total knee joint replacement. The investigators select patients without proximal thromboembolism assessed by bilateral venous ultrasound examination 7-10 days after surgery. the investigators hypothesis is that stopping thromboprophylaxis is equally effective than prolonging thromboprophylaxis in order to prevent post-surgery complications in this population.