To evaluate whether pregabalin and/or celecoxib could improve analgesic efficacy of intrathecal morphine for patients after total knee arthroplasty.

A single-dose spinal anesthesia combining with morphine for total knee arthroplasty (TKA) is a simple, economical anesthetic technique commonly used in our hospital. Still some patients could not get effective postoperative pain control. Pregabalin, an anticonvulsant, has been shown to reduce acute pain after molar extraction, laparoscopic cholecystectomy, and reduce postoperative morphine requirement after total hip arthroplasty, and celecoxib, a selective cyclo-oxygenase (COX) - 2 inhibitor, with perioperative prescription is successfully reduces pain score and opioid consumption after TKA under spinal anesthesia alone. However, no clinical study has yet investigated whether preoperative single-dose of pregabalin, celecoxib or in combination compared to placebo can improve analgesic efficacy of intrathecal morphine after TKA. The primary objective of this study was to evaluate whether these medications could reduce pain scores at rest / when movement and morphine requirement after TKA under spinal anesthesia with intrathecal morphine. Secondary outcome assessed include adverse effects, anxiety score and patients' satisfaction score.

Inclusion Criteria:

• Patients between 50-75 years of age
• Patients with an American Society of Anesthesiologists physical status of I to III
• Patients scheduled for primary TKA with a diagnosis of osteoarthritis under spinal anesthesia

Exclusion Criteria:.

• Patients had a known allergy to any of the medications being used
• a history of drug or alcohol abuse
• a history of taking chronic pain medications (ie, show-release preparations of opioids, given that morphine consumption was the primary outcome)
• a history of taking pregabalin or gabapentin / non-steroidal anti-inflammatory drugs / COX-2 inhibitors
• a psychiatric disorder
• a history of impaired renal function (Cr > 1.5 mg/dl), peptic ulcer, asthma, thrombotic cerebrocardiovascular diseases, uncontrolled hypertension
• a history of contraindication for spinal anesthesia
• a history of bleeding tendency
• pregnancy
• unable or unwilling to use patient - controlled analgesic (PCA)