Paths of femoral nerve catheters placed using ultrasound-guided in plane vs out of plane techniques: A randomized controlled clinical trial.

Background: Continuous blockade of the femoral nerve is widely used for postoperative analgesia after hip surgery. It can be achieved by ultrasound-guided placement of a femoral nerve catheter via either the in plane (IP) or out of plane (OOP) technique. On the basis of postoperative radiographs, we evaluated the paths of femoral nerve catheters with respect to both techniques and its effect on postoperative analgesia. Methods: Thirty-four patients were randomized to receive a radiopaque femoral nerve catheter via either the IP or OOP technique. The paths and tip position of the catheters were evaluated in postoperative frontal radiographs of the operated hip joint concerning a predefined target region and four neighboring regions. Pain scores were assessed using a numeric rating scale (0-10). Results: Sixteen IP patients and 18 OOP patients were included in the study. The catheter path was radiographically evaluated in 13 IP patients and in 10 OOP patients. The catheter tips were located within the target region in 39% of the IP group and in 50% of the OOP group. The catheter tip was 0.00 cm [-3.80 to 3.84] and -1.19 cm [-12.27 to 0.00] (median [range]) from the target region in the OOP group and IP group, respectively (P = .045). Catheters flipped distally more often in the IP group (IP: 61.5%, OOP: 10.0%; P = .01). There were no marked differences in the pain scores of either group. Conclusion: Femoral nerve catheters inserted by the ultrasound-guided IP technique flip distally more frequently than catheters inserted by the OOP technique. Moreover, the distance between the catheter tip and the trunk of the femoral nerve is greater for IP catheters than for OOP catheters. Despite these findings, postoperative analgesia did not seem to differ between the 2 techniques.