This prospective, randomized, controlled, and multicenter clinical study aims to compare the postoperative analgesic efficacy of two regional anesthesia techniques commonly used in knee arthroscopy: adductor canal block (ACB) and combined adductor canal block plus biceps femoris short head (ACB+BiFeS) block. The study will evaluate postoperative pain control, opioid consumption, adverse effects, hospital stay, and patient satisfaction. Findings will help determine the most effective and safe method for postoperative analgesia in knee arthroscopy patients.

Knee arthroscopy is one of the most common orthopedic procedures and is frequently associated with significant postoperative pain. Effective multimodal analgesia is therefore essential to reduce opioid consumption, improve early mobilization, and enhance overall patient recovery. Among the regional anesthesia techniques, the adductor canal block (ACB) is well established as an effective motor-sparing block that provides analgesia to the medial and anterior aspects of the knee. However, patients often continue to experience posterolateral knee pain, which is not consistently relieved by ACB alone.

Recent anatomical and cadaveric studies have described the biceps femoris short head (BiFeS) block as a promising technique for targeting the posterolateral knee compartment. The BiFeS block involves deposition of local anesthetic between the short head of the biceps femoris muscle and the lateral femoral cortex at the supracondylar level. Preliminary findings suggest that this block may provide effective analgesia for the posterolateral knee without causing significant motor impairment.

This prospective, randomized, controlled, multicenter clinical trial is designed to evaluate whether the addition of the BiFeS block to standard ACB improves postoperative analgesia compared with ACB alone in patients undergoing knee arthroscopy under spinal anesthesia. The study will investigate pain scores at rest and during movement, total opioid consumption, side effects, rescue analgesic requirements, and quality of recovery. The dermatomal distribution of the blocks will be optionally assessed using cold testing.

By directly comparing ACB and combined ACB+BiFeS block under standardized perioperative conditions, this study seeks to generate high-quality evidence on the clinical utility of BiFeS as an adjunct technique. The results are expected to guide anesthesiologists in selecting optimal regional analgesia strategies for knee arthroscopy, with the potential to improve patient satisfaction, reduce opioid-related complications, and shorten hospitalization.

Inclusion Criteria:

• Age ≥ 18 years
• ASA physical status I-III
• Scheduled for elective knee arthroscopy under spinal anesthesia
• Ability to provide written informed consent

Exclusion Criteria:

• Coagulopathy or bleeding diathesis
• Current use of anticoagulant therapy
• Known allergy or contraindication to local anesthetics used in the study
• History of diabetes mellitus with neuropathy or other neuropathic disorders
• Contraindications to regional anesthesia techniques
• Refusal to participate

Participants will be blinded to group allocation. Outcome assessors recording pain scores, opioid consumption, and side effects will be blinded to the intervention. The anesthesiologists performing the blocks cannot be blinded due to the nature of the procedures.