The anesthesiologist will insert a catheter close to the femoral nerve, at the junction of the thigh and torso immediately before beginning of anesthesia for surgery. The usual medication will be used to make installation more comfortable. The exact location where the catheter will be put into place will be identified using an ultrasound machine. This device will allow the anesthesiologist to identify the various anatomical structures. A specially designed needle will be inserted next to the femoral nerve, and its position will be confirmed with a neurostimulator. Once the adequacy of needle position is confirmed, the anesthesiologist will introduce 3 cm(Group 1) or 7 cm (Group 2)of the catheter through the needle, and then will withdraw the needle. The catheter will be fixed in place to avoid displacement.