Background: Ultrasound has increased the efficacy of femoral nerve catheters but their postoperative dislocation still remains a common problem. Although catheter placement parallel to the nerve seems to reduce dislocation rates in other nerves and plexuses, the possible advantage for femoral nerve catheter placement remains unclear.
Objective: To compare the dislocation rates of femoral catheters when placed perpendicular or parallel to the femoral nerve.
Design: Randomised controlled study.
Setting: University orthopaedic hospital. Duration of study: October 2018 to June 2019.
Patients: Eighty patients scheduled for major knee surgery with femoral catheter were enrolled and randomly allocated in two groups. Data from 78 patients could be analysed.
Interventions: The femoral nerve catheters was placed perpendicular to the nerve in Group 1 (n=40), whereas in Group 2 (n=38) parallel to it. For Group 1 the short-axis view of the nerve and an in-plane puncture was used. For Group 2 we used the short-axis view of the nerve and an out-of-plane puncture technique combined with rotation of the transducer to the long-axis view with the needle in-plane.
Main outcome measures: Primary outcome was the catheter dislocation rate in the first 48 h. Secondary outcomes were pain scores and sensory blockade.
Results: There was no statistically significant difference between the two techniques regarding dislocation of the catheters at 24 or 48 h (at 48 h, Group 1: 15%, Group 2: 2.6%, P = 0.109). Also pain scores, sensory blockade and rescue doses of ropivacaine did not differ between the groups. However, in Group 2 the technique took longer.
Conclusion: Rotating the ultrasound probe to the long-axis in-plane view enabled examination of the catheter position when it was placed parallel to the nerve. The parallel placement of the catheter required more time, but did not significantly improve dislocation rate, pain scores or sensory blockade.
Trial registration: Clinicaltrials.gov identifier: NCT03693755.