Objective: To determine whether FNB using 0.25% or 0.5% bupivacaine provided better analgesia with less effect on quadriceps strengths after ACL reconstruction.

Material and Method: One hundred patients were randomized to receive FNB with 20 mL of 0.25% or 0.5% bupivacaine. Data regarding demographic, effectiveness of FNB, time to first pain, time to first analgesic, pain scores, morphine use, and recovery of sensory and motor function were recorded.

Results: Median time to first morphine requirement was 12 hours in 0.5% bupivacaine group and 10 hours in 0.25% bupivacaine group (p = 0.048). Pain score at 18 hours was lower in 0.5% bupivacaine group compared with 0.25% bupivacaine group (p = 0.001). When specify to the patellar tendon graft subgroup, the patients requiring morphine were 70% in 0.5% bupivacaine group and 90% in 0.25% bupivacaine group (p = 0.03). No differences were found in demographic data, effectiveness of FNB, time to first pain, morphine consumption, and recovery of sensorimotor function.

Conclusion: FNB with 0.5% bupivacaine provided longer time to first analgesic and lower narcotic requirements after patellar tendon graft ACL reconstruction when compared to 0.25% bupivacaine. Both concentrations showed similar effect on quadriceps strengths.

Keywords: Femoral nerve block, 0.5% bupivacaine, 0.25% bupivacaine, Arthroscopic anterior cruciate ligament (ACL) reconstruction