Ultrasound-guided continuous femoral nerve block for analgesia after total knee arthroplasty: catheter perpendicular to the nerve versus catheter parallel to the nerve.

Background And Objectives: This study tested the hypothesis that, in continuous femoral nerve block (CFNB) under ultrasound guidance, placing a catheter perpendicular to the nerve can shorten the time of catheter insertion while providing a similar quality of analgesia compared with placing a catheter parallel to the nerve.

Methods: Fifty patients undergoing total knee arthroplasty were randomly assigned to receive ultrasound-guided CFNB either with the catheter parallel to the nerve technique (parallel group, n = 25) or with the catheter perpendicular to the nerve technique (perpendicular group, n = 25). Patient-controlled morphine analgesia pumps were available to all the patients after surgery. The time of catheter insertion, failure rates, pain scores, morphine consumption, nausea and vomiting, and maximal degree of knee flexion were recorded.

Results: The time of catheter insertion was shorter in the perpendicular group than in the parallel group (12 +/- 3 versus 22 +/- 6 mins, P < 0.01). Failed catheter insertion occurred in 3 (12%) of 25 patients in the parallel group and in none of 25 patients in the perpendicular group (P = 0.2347). There were no significant differences in pain scores, opioid consumption, incidence of nausea and vomiting, and maximal degree of knee flexion between the 2 groups.

Conclusions: In CFNB under ultrasound guidance, using the catheter perpendicular to the nerve technique can shorten the time of catheter insertion while providing a similar quality of analgesia after total knee arthroplasty as compared with the catheter parallel to the nerve technique.