Ambulatory Continuous Femoral Analgesia for Major Knee Surgery: A Randomised Study of Ultrasound-Guided Femoral Catheter Placement

Needle-nerve stimulation has a false negative motor response rate, which may increase needle passes. This prospective, randomised study tested the hypothesis that femoral nerve catheters placed with ultrasound-only guidance could provide comparable postoperative analgesia to those placed using a conventional nerve stimulation endpoint. Patients presenting for major knee surgery to the lead investigator were recruited. Needles introduced for femoral nerve catheter placement were initially guided with ‘oblique’ out-of-plane ultrasound imaging but were then prospectively randomised to either an ultrasound (n=21) or nerve stimulation (n=24) endpoint. An elastomeric infusion of ropivacaine 0.2% 2 ml/hour with as required hourly 5 ml boluses was continued for >48 hours in hospital and/or in the home. Needle time under the skin and numerical rating pain score during insertion were recorded. Patients were questioned for worst numerical rating pain score, the need for supplementary ropivacaine boluses and tramadol on postoperative days one and two. There was no difference in the worst numerical rating pain score at rest and on movement and the requirement for supplementary ropivacaine boluses or tramadol during the first 48 postoperative hours. The median (quartiles) needle time under the skin was 58 seconds (51 to 76) in the ultrasound group and 120 seconds (95 to 178) in the nerve stimulation group (P=0.001). The median (quartiles) insertion numerical rating pain score was 2 (0 to 2) in the ultrasound group and 4 (2 to 6) in the nerve stimulation group (P=0.014). Femoral nerve catheters placed for major knee surgery using an ultrasound endpoint provided postoperative analgesia comparable to that obtained when using a nerve stimulation endpoint and were associated with a reduction in both needle manipulations and procedure-related pain.