Effectiveness of Retrolaminar Block in Lumbar Spine Fusion With Multimodal Analgesia

This randomized, blinded, controlled clinical trial aims to evaluate the effectiveness of ultrasound-guided retrolaminar block in reducing postoperative opioid consumption in patients undergoing lumbar spine fusion surgery under multimodal analgesia. The participants will: * Be randomly assigned in a 1:1 ratio to receive either a retrolaminar block with 0.25% bupivacaine plus epinephrine or a sham block (normal saline) prior to surgical incision. * Receive standardized multimodal analgesia. * Have follow-up by the Acute Pain Unit during the first 3 days, to assess opioid consumption (morphine) in 24 hours, pain intensity measured by Numeric Rating Scale, quality of recovery assessed by the QoR-15 questionnaire, intraoperative blood loss, and postoperative complications.

Inclusion Criteria: * Adults aged 18-75 years, scheduled for lumbar spine fusion surgery by a trauma team * American Society of Anesthesiologists (ASA) Classification I-III * Willing and able to provide written informed consent to participate in the study. Exclusion Criteria: * History of chronic use of strong or weak opioids for more than 3 months. * Diagnosis of chronic pain and treatment by a pain management team. * ASA score greater than or equal to 4. * Patients with prior lumbar spine surgery. Spinal instrumentation at the surgical site. * Estimated creatinine clearance less than 60 ml/min. * Coagulation disorder or abnormal coagulation tests. * Infection at the surgical site. * Weight less than 50 kg. * Altered mental status that prevents reliable evaluation. * Allergy to local anesthetics or analgesic drugs used in the study. * Patients with contraindications to peripheral nerve blocks. * Lumbar spine fixation due to oncologic disease or acute trauma. * Use of intraoperative neuromonitoring and TIVA.