After the 8 hour assessment, all patients (excluding technical failures but including "anaesthetic failures") will start a femoral perineural infusion with levobupivacaine or ropivacaine at a rate of 10ml h-1 and concentration of 1μM.ml-1 (400μM in 400ml elastomeric ball) for 48 hours.Patients classed as "technical failure" will have a femoral perineural catheter reinserted.