Minimum Effective Dose of Incisional Local Infiltration Betamethasone for the Prevention of Pain After Spinal Surgery

Inclusion Criteria: Patients scheduled for spine surgery under general anesthesia. Anticipated cervical, thoracic, and lumbar spine surgeries (within three level). Patients age 18-65 years. American Society of Anaesthesiologists Classification of I or II. Exclusion Criteria: Patients refuse to participate. Patients who are allergic to ropivacaine, betamethasone and opioid, . Pateints who have been abusing drugs or alcohol. Patients who have abnormalities in kidney or liver function tests. BMI\<15kg/m2 or\>35 kg/m2. Patient has a history of spinal surgery. Patient has peri-incisional infection. Patient has a history of stroke or other serious neurological disease. Patient has a history of diabetes and other metabolic disorders. Patient has a history of psychological disorders. Patient is on systemic steroids. Patient is pregnant or breastfeeding. Glasgow Coma Scale score \< 15 before surgery. Unable to provide written informed consent. Withdrawal criteria: Voluntary withdrawal. Delayed extubation. Poor cognitive function within 48 hours after surgery. Postoperative radiation therapy or chemotherapy during follow-up. Postoperative diagnosis of spinal cord or nerve root injury resulting in pain during follow-up. Reoperation during follow-up.