Background and Objectives Femoral nerve block is effective in reducing postoperative pain after inpatient knee surgery. We studied its efficacy compared with standard analgesia following outpatient anterior cruciate ligament repair, including the duration of analgesia and the effect of different concentrations of bupivacaine.

Methods After Institutional Review Board approval and informed consent, we prospectively randomized patients to receive, in a blinded fashion, either a sham block, a femoral nerve block with 25 mL 0.25% bupivacaine, or with 25 mL 0.5% bupivacaine after anterior cruciate ligament repair under epidural anesthesia. Verbal analog pain scores were evaluated by a blinded observer at 20 and 40 minutes after injection. Patients with pain >4 (out of 10) were assessed for the presence of a block and offered a supplemental block if no anesthesia was present at either evaluation. By prospective agreement, any study group with 6 failures was excluded from further recruitment. After discharge, patients recorded pain scores and analgesic consumption in a diary, and estimated the time at which they perceived that analgesia and sensory block from the femoral nerve block resolved, based on an increase in pain, sensation, and strength in the leg.

Results In the sham block group, 6 of 12 patients reported inadequate analgesia in the postanesthesia care unit (4 at 20 minutes, 2 at 40 minutes; greater than other groups, P < .003) and were excluded from further study. Patients with sham blocks had higher pain scores 20 minutes after the block, and requested intravenous analgesia more often. Bupivacaine 0.25% and 0.5% provided 23.2 ± 7 and 25.7 ± 11 hours of analgesia, respectively.

Conclusions Femoral nerve block with 0.25% bupivacaine contributes significantly to multimodal postoperative analgesia in the immediate postoperative period following outpatient anterior cruciate ligament repair. Both doses of bupivacaine studied provided analgesia for the first night after surgery.