Perineural Dexamethasone for Continuous Femoral Nerve Block

"1\) Arm l (dexamethasone group) Ultrasound-guided femoral nerve block with 1% lidocaine 15 ml after the end of surgery Postoperative femoral nerve patient controlled analgesia~* Total volume 250 ml (0.375% ropivacaine 60 ml + normal saline 188 ml + dexamethasone 10 mg (2 ml))~* Basal rate 4 mL/hr, Bolus volume 2 mL, Lock-out time 15 min"

"2\) Arm ll (sham group) Ultrasound-guided femoral nerve block with 1% lidocaine 15 ml after the end of surgery Postoperative femoral nerve patient controlled analgesia~* Total volume 250 ml (0.375% ropivacaine 60 ml + normal saline 190 ml~* Basal rate 4 mL/hr, Bolus volume 2 mL, Lock-out time 15 min"