A randomized comparison of long-axis and short-axis imaging for in-plane ultrasound-guided popliteal-sciatic perineural catheter insertion

Purpose Ultrasound-guided long-axis in-plane sciatic perineural catheter insertion has been described but not validated. For the popliteal-sciatic nerve, we hypothesized that a long-axis in-plane technique, placing the catheter parallel and posterior to the nerve, results in faster onset of sensory anesthesia compared to a short-axis in-plane technique. Methods Preoperatively, patients receiving a popliteal-sciatic perineural catheter were randomly assigned to either the long-axis or short-axis technique. Mepivacaine 2 % was administered via the catheter following insertion. The primary outcome was time to achieve complete sensory anesthesia. Secondary outcomes included procedural time, onset time of motor block, and pain on postoperative day 1. Results Fifty patients were enrolled. In the long-axis group ( n = 25), all patients except 1 (4 %) had successful catheter placement per protocol. Two patients (8 %) in the long-axis group and 1 patient (4 %) in the short-axis group ( n = 25) did not achieve sensory anesthesia by 30 min and were withdrawn. Seventeen of 24 (71 %) and 17 of 22 (77 %) patients in the short-axis and long-axis groups, respectively, achieved the primary outcome of complete sensory anesthesia ( p = 0.589). The short-axis group ( n = 17) required a median (10th–90th ‰) of 18.0 (8.4–30.0) min compared to 18.0 (11.4–27.6) min for the long-axis group ( n = 17, p = 0.208) to achieve complete sensory anesthesia. Procedural time was 6.5 (4.0–12.0) min for the short-axis and 9.5 (7.0–12.7) min for the long-axis ( p < 0.001) group. There were no statistically significant differences in other secondary outcomes. Conclusion Long-axis in-plane popliteal-sciatic perineural catheter insertion requires more time to perform compared to a short-axis in-plane technique without demonstrating any advantages.