Ultrasound-guided femoral catheter placement: a randomised comparison of the in-plane and out-of-plane techniques

In-plane vs out-of-plane needle-probe alignment for perineural catheter placement remains controversial. Patients presenting for major knee surgery were randomly assigned to out-of-plane (n = 42) or in-plane (n = 39) needle-probe alignment for femoral nerve catheter placement, with both techniques using short-axis nerve imaging. Twenty millilitres of ropivacaine 0.5% was administered via the catheter followed by a ropivacaine elastomeric infusion incorporating on-demand boluses. All patients received pre-operative single-injection sciatic and obturator blocks and general anaesthesia. The primary outcome, numerically rated worst pain on movement (0-10) during the first 24 h, demonstrated equivalence within two points of the scale at a 5% significance level using two one-sided tests (corresponding 90% CI -1.2 to 0.6). There were no differences between groups for all secondary outcomes, including numerically rated worst rest pain, ropivacaine bolus and tramadol consumption. These results suggest that for ultrasound-guided femoral catheter placement using short-axis nerve imaging, operators should use the needle-probe alignment technique with which they are most familiar.