Quadriceps muscle strength is an important determinant of quality of recovery in elderly patients after total knee arthroplasty. We try to compare the quadriceps muscle strength change between 0.2 % ropivacaine continuous fixed femoral infusion and patient controlled femoral analgesia group.

Continuous femoral nerve analgesia technique is relatively safe, can be easily trained, and reduces significantly intravenous opioid consumption. These favorable features make it standard treatment option for postoperative knee pain. However, direct perineural local anesthetic effect is not only confined into pain fiber, but, the other sensory and motor nerve fibers. Therefore, unwanted motor weakness is accompanied. Quadriceps muscle strength, which is important determinant of physical function after knee arthroplasty, can be influenced in continuous femoral nerve block. Various local anesthetic infusion techniques have been suggested to minimize the change of quadriceps muscle strength. Decreasing local anesthetic concentrations affect not only degree of muscle weakness, but also reduces the quality of pain control. Different anatomic location of catheter tip, considering motor fiber in posterior part of femoral nerve, could not reduce motor weakness. In a study with continuous popliteal-sciatic nerve blocks after hallux valgus repair, repeated bolus administration seems to be more effective method for pain control without concurrent motor impairment. However, another study with continuous femoral nerve block in healthy volunteers, hourly repeated bolus dose of 5 ml of 0.1% ropivacaine failed to spare motor block. Previously, our institution standard technique is fixed continuous infusion of 0.2% ropivacaine and concomitant intravenous patient controlled fentanyl. Because physical therapy of our institution, usually starts with the 2nd day of operation, so, we assume that continuous fixed infusion may result in more drug accumulation near nerve fiber. So, patient controlled mode of femoral analgesia could be better choice for initiation of physical therapy. At the same time, comparison between patient controlled analgesia and continuous infusion is not fully elucidated until recently. Therefore, in this study, we try to compare quadriceps muscle strength change between continuous infusion and patient controlled femoral analgesia in patients undergoing total knee replacement arthroplasty. Secondary outcomes include sensory effect in femoral nerve distribution, pain scores, iv fentanyl consumption, and other adverse effects.

Inclusion Criteria:

• > 21, or < 80 years old- men and women
• primary, unilateral total knee replacement surgery
• spinal anesthesia

Exclusion Criteria:

• general anesthesia
• secondary knee replacement surgery
• patient refusal for continuous femoral nerve analgesia technique
• abnormal coagulation profile, e.g. Prothrombin time international normalized ratio > 1.5, activated partial thrombin time > 50 sec
• within 5 days after termination oral antiplatelet agent
• Body mass index>45
• impaired renal function
• infection near femoral area
• previous injury near femoral area
• neurologic dysfunction in lower limb
• previous adverse drug reaction for local anesthetics
• American society of anesthesiologists (ASA) class III, iV or V