The primary aim of this randomized, double-blind study is to examine a perioperative analgesic strategy utilizing both ketamine and methadone in patients undergoing posterior spinal fusion. Patients randomized to the ketamine group will be given 0.2 mg/kg of methadone at anesthetic induction, and a ketamine infusion will be used intraoperatively and for 48 hours after surgery. Patients in the control group will receive 0.2 mg/kg of methadone at anesthetic induction, and then a D5W (sugar water) infusion intraoperatively and for 48 hours postoperatively. The total amount of PCA hydromorphone used postoperatively will be recorded, as well as postoperative pain scores. Recovery variables will be measured and patients will be assessed for adverse events potentially related to opioids and ketamine. NMDA receptor stimulation is also thought to play an important role in the development of chronic pain after surgery. Therefore, patients will be surveyed about chronic postsurgical pain 1, 3, 6, and 12 months after the operation to determine whether intraoperative management may influence the development of long-term adverse events.