The efficacy of femoral nerve block in pain reduction for outpatient hamstring anterior cruciate ligament reconstruction: A double-blind, prospective, randomized trial

The purpose of this study was to assess the efficacy of intraoperative femoral nerve block (FNB) in the reduction of postoperative pain following anterior cruciate ligament (ACL) hamstring reconstruction. Patients undergoing primary ACL reconstruction with hamstring tendon graft under general anesthetic who had signed an informed consent were included in the study. Patients were stratified to 4 surgeons and randomized to FNB with 0.25% bupivacaine or placebo of normal saline injected into the femoral nerve sheath before reversal of the general anesthetic. All patients received an intra-articular injection of bupivacaine at the beginning of their operative procedure. A single technique that included the use of a peripheral nerve stimulator was used for all FNBs. All patients were discharged on the day of surgery and given prescriptions for Tylenol 3. The Short-Form McGill Pain Questionnaire (SF-MPQ), a visual analog scale (VAS) for pain, and a medication diary recording Tylenol 3 usage were completed by patients in the recovery room, on the night of surgery, and on postoperative days 1, 2, and 3. There were complete data for 61 patients (FNB, 29; placebo, 32). An analysis of variance (ANOVA) test of the data showed no significant difference between the FNB and placebo group for pain reduction over the combined study period for both the SF-MPQ and VAS. However, the ANOVA does suggest that, on the night of surgery, there was a significant reduction in pain as measured with the VAS in the FNB group. A Student t test performed on the night of surgery data (SF-MPQ, P = .131; VAS, P = .0114; Tylenol 3, P = .076) showed a statistically significant difference between the FNB (39.4 +/- 21.0 mm) and placebo (56.8.0 +/- 24.6 mm) measured by VAS. Because this represented a difference of only 1.74 cm on a 10-cm VAS, it is unlikely to be clinically relevant. No difference was found in the amount of analgesic required on any day postoperatively. In conclusion, FNB may reduce pain on the night of surgery. However, this may not be clinically significant. FNB is not recommended at this time for use in outpatient ACL reconstruction with hamstring graft.