Quadriceps Strength After ACL Reconstruction: Femoral Nerve Block Versus Adductor Canal Nerve Block

Abstract

Anterior cruciate ligament reconstruction (ACLR) is one of the most common orthopedic sports medicine procedures performed on an outpatient basis. In patients undergoing ACLR, attention has been focused on providing adequate pain relief while limiting postoperative quadriceps weakness. Femoral nerve block (FNB) has been the mainstay of treatment in the past. Recent articles debate the efficacy of femoral nerve block versus adductor canal block (ACB) regarding pain control and residual quadriceps weakness after ACLR. This study was undertaken to identify if a difference exists in quadriceps strength at multiple time points after an ACB or FNB in ACLR utilizing only hamstring autograft. An IRB approved prospective double-blinded study of patients less than 18 years of age undergoing primary ACLR utilizing only hamstring autograft were enrolled. All patients were randomized to receive an ACB or FNB at the time of surgery and the surgeon was blinded to the block type. A dynamometer was used to measure the knee extension strength of both the operative and non-operative leg preoperatively and at multiple times postoperatively until completion of the MOON rehabilitation protocol. Tourniquet time, pain scores and time to complete physical therapy were collected. Sixty-one patients underwent ACLR and were evaluated. There was no significant difference in patient age, tourniquet time, pain scores or time to complete physical therapy between the FNB (n=26) and ACB (n=35) groups. Patients who received a femoral nerve block had a statistically significant quadriceps motor strength deficit at 4 hours (P=.01) and 6 weeks (P=.02) postoperatively compared to those who received an adductor canal block. At 3 (P=.17) and 6 (P=.31) months, there was no statistically significant difference in quadriceps motor strength between the two groups. There was also no significant difference in re-tear rate between the two groups. Although there were early statistically significant quadriceps motor strength deficits, in the femoral nerve block group compared to the adductor canal block group, it did not persist after the 6 week postoperative time period. Adductor canal nerve block does not provide a persistent statistically significant quadriceps strength benefit over femoral nerve block in adolescent patients undergoing anterior cruciate ligament reconstruction utilizing autologous hamstrings.