The Comparison of Postoperative Analgesia Between Adductor Canal Block and Femoral Nerve Block After Arthroscopic ACL Reconstruction With Hamstring Graft: A Randomized Controlled Trial

After approval from institutional ethic committees, Thammasat University Hospital, patients who meet the eligible criteria will be asked for informed consent. Randomization will be performed by computerization with varied block sizes (4 and 6), and the sequence of randomization will be concealed by sealed envelopes. Once given informed consent, the investigator opened the sealed envelope, which randomized the patient to the adductor canal block group (ACB), or the femoral nerve block group (FNB).

The day before surgery day, patients who meet the eligible criteria will ask for the informed consent from blinded research assistant. They will obtain patients' demographic data, preoperative pain scores, and quadriceps strength. They will be recommended how to evaluate pain score and use the patient-controlled analgesia.

In the block room, patients will be sedated with midazolam 2-3 mg intravenously. The nerve block will be performed before spinal anesthesia by unblinded anesthesiologists. During block, the patients will be blinded by sham block. In ACB group, patients will receive sham block of femoral nerve at inguinal area, and then ACB will be performed, while in FNB group, patients will receive FNB, and then sham block will be performed in the mid-femoral area.

After standard monitored, the saphenous nerve will be blocked in the ACB group under ultrasound guidance using linear probe (9 mHz, GE Healthcare®) with nerve stimulator (Payunk®) at midfemoral level. When the needle tip is positioned, the nerve stimulator is turned on and set to deliver a current of 0.5 mA at a frequency of 2 Hz and pulse duration of 0.1 ms. The presence of a quadriceps muscle twitch, if elicited, will be recorded, and the needle was re-positioned until the muscle twitch disappeared. Then, 0.5% levobupivacaine with adrenaline 5 µg/ml 15 ml will be injected.

The femoral nerve block is also performed in the FNB group under ultrasound guidance using linear probe (9 mHz, GE Healthcare®) and nerve stimulator (Payunk®). With ultrasound guidance, the femoral nerve is identified in femoral triangle near to femoral artery, and when the needle tip is in proper position in the ultrasound image, the nerve stimulator is used to confirm, the presence of quadriceps twitching at the current less than 0.5 mA, and the absence of quadriceps twitching at the current more than 0.2 mA. After that, 30 ml of 0.25% levobupivacaine with adrenaline 5 µg/ml is injected.