The study aims to compare the use of intravenous patient controlled analgesia (IVPCA) versus the delivery of pain relief (per oral and intravenous (IV) medications as rescues analgesia) on an as needed basis within a well defined fast track protocol that includes multimodal analgesia for patients who are undergoing elective primary knee replacement surgery. The investigators assumed that with the multimodal analgesia regimen without the use of IVPCA will demonstrate decreased consumption of postoperative opioids, reduced incidence of opioids related side effects and decreased length of stay in the hospital.

Inclusion Criteria:

• Male or female patients aged 18 to 80 years old
• Provision of written informed consent
• Patients scheduled to undergo primary knee surgery included in the fast track protocol under regional anesthesia only
• Patients with Body Mass Index (BMI) between 18 to 34.9
• Patients with American Society of Anesthesiologists (ASA) physical status classification of 1 to 3

Exclusion Criteria:

• Patients on chronic (more than twice a week) opioid treatment including Tylenol #3, percocet, morphine, methadone, hydromorphone, fentanyl patch and other potent opioids
• Patients with language barrier or difficulty in communication in English
• Patients who are allergic to morphine and hydromorphone, fentanyl, gabapentin, celecoxib or acetaminophen
• Patients with increased risk for respiratory depression with intrathecal morphine (OSA, central apnea)
• Patients with documented Renal or hepatic impairment