This study will evaluate whether ultrasound-guided quadro-iliac plane block provides better postoperative pain control than local infiltration analgesia in patients undergoing single-level lumbar microdiscectomy.

Adult patients scheduled for elective single-level lumbar microdiscectomy will be randomly assigned to receive either bilateral quadro-iliac plane block plus patient-controlled analgesia or local infiltration analgesia plus patient-controlled analgesia. The main outcome of the study will be total fentanyl consumption during the first 24 hours after surgery. Pain scores, need for rescue analgesia, opioid-related side effects, patient satisfaction, and recovery quality will also be evaluated.

This is a prospective, randomized, double-blind, controlled, multicenter clinical trial designed to assess the analgesic efficacy of ultrasound-guided quadro-iliac plane block in patients undergoing elective single-level lumbar microdiscectomy.

Patients aged 18-75 years with American Society of Anesthesiologists physical status I-III who are scheduled for elective single-level lumbar microdiscectomy under general anesthesia will be included. Participants will be randomized into two groups. The intervention group will receive bilateral ultrasound-guided quadro-iliac plane block before emergence from anesthesia, followed by postoperative patient-controlled analgesia. The control group will receive local infiltration analgesia performed by the surgeon, followed by postoperative patient-controlled analgesia.

All patients will receive a standardized general anesthesia protocol. Postoperative analgesia will be provided using a fentanyl-based patient-controlled analgesia device. The primary outcome will be total fentanyl consumption during the first postoperative 24 hours. Secondary outcomes will include numerical rating scale pain scores at predefined postoperative time points, rescue analgesic requirement, opioid-related adverse effects such as nausea, vomiting, pruritus and respiratory depression, dermatomal sensory spread, and patient-reported recovery quality using the QoR-15 questionnaire.

Inclusion Criteria:

• Adults aged 18 to 75 years
• American Society of Anesthesiologists physical status I to III
• Scheduled for elective single-level lumbar microdiscectomy, such as L4-L5 or L5-S1 disc herniation
• Planned surgery under general anesthesia
• Able to provide written informed consent

Exclusion Criteria:

• Allergy or hypersensitivity to local anesthetics
• Coagulopathy or active anticoagulant use
• Infection, scar tissue, or skin lesion at the injection site
• Pregnancy or breastfeeding
• Chronic pain syndrome or regular opioid use
• American Society of Anesthesiologists physical status IV or higher
• Planned surgery for two or more levels of disc herniation

Participants and the postoperative outcomes assessor will be blinded to group allocation. The anesthesiologist performing the block procedure will not take part in postoperative data collection or outcome assessment.