Inclusion Criteria:  Male gender. Age range of 18-60 years. Scheduled for open lumbar decompression surgery. A minimum of 1-year experience of drug consumption or having drug withdrawal symptoms when stopping for inclusion in the drug addicts group(according to the patient's statement and rapid opiate urine test).  Exclusion Criteria:  Hepatic or renal insufficiency. Preoperative cognitive dysfunction or communication disorder. Allergy to amide-type local anaesthetics. Back puncture site infection. Coagulation disorders. Emergency surgery.