The investigators will compare the results of sono-guided femoral nerve block in arthroscopic surgery for anterior cruciate ligament reconstruction under spinal anesthesia.

This study is a randomized controlled trial of 100 patients, who underwent history taking, physical examinations, x-rays, and MRI or ultrasonography, and were diagnosed with anterior cruciate ligament rupture from september 2023 to august 2028. The 100 patients will be assigned to Group I (with femoral nerve block) or Group II (without femoral nerve block) under double-blinded randomization. The randomization will be performed by an independent nurse using a computerized random sequence generator. The operators who participated in the procedure will be blinded to the participant's information. Both group will undergo spinal anesthesia for arthroscopic anterior cruciate ligament reconstruction. After anesthesia, sono-guided femoral nerve block will be performed. The injection for group1 is 20 mL ropivacaine and for groupII is 20 mL 0.9% saline. A visual analog scale (VAS) for pain will be recorded 1, 3, 6, 12, 18, 24, 36, 48 hours after the operation. VAS scores range from 0 to 10, with 0 being no pain and 10 being the most severe pain ever experienced. Injection with ultrasonography will be performed by a single anesthesiologist. 3 orthopedic surgeons will perform the surgery.

Inclusion Criteria:

• individuals who are scheduled to undergo arthroscopic anterior cruciate ligament reconstruction surgery and must be received sufficient explanation about the research prior to surgery and have provided their informed consent to participate.

Exclusion Criteria:

• who require simultaneous surgery for concomitant cartilage injury, medial meniscus tear, and lateral collateral ligament tear.
• who have previously undergone surgical treatment within the knee joint.
• who have declined to participate in the research.
• where medical, surgical, or anesthetic complications occurred during surgery.
• other cases deemed necessary by the researchers.