Postoperatively, 6 hours after the initial bolus, a local anaesthetic infusion line was connected to the micro filter of the PNC. All patients received patient-controlled perineural analgesia (basal rate 5 ml/h, bolus 4 ml, lock-out time 20 min) with ropivacaine 0.3% for 24 hours, and then reduced to ropivacaine 0.2%.