Patients who undergoing total knee arthroplasty under spinal analgesia will be recruited and randomly assigned to the following two groups according to the regimen of PCA: (A) opioid group who receive only fentanyl citrate 1200mcg for continuous infusion drug, (B) non-opioid group who receive ketorolac tromethamine 150mg with nefopam hydrochloride 100mg for continuous infusion drug. All the patients will receive additional fentanyl citrate as bolus injection drug if they need more analgesics postoperatively.

Inclusion Criteria:

• ASA physical status I-II
• undergoing elective total knee arthroplasty under spinal anesthesia

Exclusion Criteria:

• history of stomack ulceration
• increased ICP
• bronchial asthma
• allergy on aspirin, NSAIDs, Nefopam
• drug user of antiplatelet or anticoagulant