Postoperative Period All blocks were performed in the Post Anaesthesia Care Unit immediately after surgery with standard anesthetic monitoring and an IV cannula in place. No subcutaneous local anesthetic or sedation were required as the spinal anesthetic was still effective. All patients received an adductor canal block under ultrasound guidance using a high frequency probe at the mid thigh level. After appropriate asepsis local anesthesia to the skin was placed at the level of the mid femur on the medial aspect of the thigh. Using ultrasound guidance (General Electric Venue 40, 3050 Lake Drive, Citywest Business Campus, Dublin 24, Ireland) with a high frequency L12 linear transducer the femoral artery was visualized in cross section and the ultrasound needle (B Braun Contiplex D ultrasound needle and catheter set, B Braun Melsungen AG, 34209 Melsungen, Germany) placed using in-plane visualization below the Sartorius muscle and just lateral to the femoral artery and medial to the Vastus Medialis. All patients received an injection of bupivacaine 0.5% 10 ml. For patients allocated to receive a continuous infusion postoperatively, a catheter was inserted immediately after injection of the initial bolus of local anesthetic. Patients allocated to the single injection group received the injection of local anesthetic followed by placement of a sham catheter on the skin, covered with a large opaque dressing. (Figure 3) In both groups, patients' catheters were attached to the concealed in opaque bags. The sham pumps were filled with normal saline. The pumps containing local anesthetic contained 0.15625% bupivacaine 350 ml were set to run at 8 ml/ hour (the equivalent of 0.125 % bupivacaine running at 10 ml/hour) All blocks were placed by Consultant anesthesiologists with fellowship training in Regional Anaesthesia.