For CFNB: Images of the femoral nerve will be obtained in the short axis. 1% lidocaine will be used for local infiltration of the skin. A 2 inch 18 G touhy needle ( B Braun) will be advanced in plane under US guidance . Confirmation may take place with Quadricpes muscle twitches and patella movement between 0.3 and 0.4mA (2Hz; 0.1ms). A bolus of 20 ml of Ropivicaine 0.5% will be injected. A non stimulating catheter will be advanced through the needle to a distance of 3-4 cm beyond the needle tip. Catheter will be secured in place using benzoin, Steristrips, and a tegaderm.