Forty patients of American Society of Anesthesiologist physical status Ⅰor Ⅱ undergoing total knee arthroplasty under spinal anesthesia would be enrolled and randomly divided into two groups (R, "3-in-1" using a 30 ml of ropivacaine 0.375% and a continuous 3-in-1 with a ropivacaine 0.2%(8mL/h) for 48 h after operation, RF: Fifty ug of fentanyl will be added to a bolus(30ml ropivacaine 0.375%) and 1ug/ml of fentanyl will be mixed to a continuous infusion(8mg/h, ropivacaine 0.2%). Spinal anesthesia will be done after the insertion of femoral catheter. IV PCA with hydromorphone(0.15mg/ml, 0-1-10), will be used for rescue analgesics. Visual analgesia scale, hydromorphone consumption, side effects until 48h after operation and satisfaction will be compared.