Continuous versus single-injection sciatic nerve block added to continuous femoral nerve block for analgesia after total knee arthroplasty: a prospective, randomized, double-blind study.

BACKGROUND AND OBJECTIVES

The benefit of adding sciatic nerve block (SNB) to femoral nerve block to improve analgesia after total knee arthroplasty (TKA) is uncertain. We hypothesized that the effective duration of single-injection SNB is too short to improve postoperative analgesia and that this contributes to conflicting results on the efficacy of SNB after TKA. We evaluated this hypothesis in a prospective double-blind randomized controlled trial.

METHODS

Sixty patients undergoing TKA were randomly allocated to a continuous SNB group or a single-injection SNB group. All patients received femoral nerve block (0.5% ropivacaine 20 mL) and SNB (0.2% ropivacaine 20 mL) and catheters were inserted into both peripheral nerve block sites before surgery. Both groups received continuous femoral nerve block and patient-controlled intravenous analgesia with morphine. Continuous SNB (0.2% ropivacaine 5 mL/h; continuous SNB group) or sham continuous SNB (0.9% normal saline 5 mL/h; single-injection SNB group) was provided after surgery. The primary outcome was total morphine consumption for 48 hours after surgery.

RESULTS

Total morphine consumption in the 48-hour period after surgery was significantly lower in the continuous SNB group compared with the single-injection SNB group [4.9 (5.9) vs 9.7 (9.5) mg, P = 0.002]. Visual analog scale pain scores at rest were also significantly lower in the continuous SNB group (P = 0.035).

CONCLUSIONS

The combination of continuous femoral and SNB provides a superior opioid sparing effect and improves analgesia after TKA.