Early mobilization and rehabilitation can be difficult after total knee arthroplasty (TKA) due to a high incidence of moderate to severe postoperative pain. Non-steroidal anti-inflammatory drugs (NSAIDs) are important to multimodal analgesic protocols. Parecoxib is an NSAID that selectively inhibits the enzyme cyclooxygenase-2 (COX-2). Clinical trials have shown that it does not alter platelet function or gastric mucosa. A recent study, after comparing ketorolac and parecoxib used at the same time in infiltration and systemically, found no differences in perioperative analgesia with a tendency to less bleeding in the parecoxib group. This randomized study will compare the effectiveness of adding a COX-2 inhibitor in the pain management of patients undergoing TKA as part of a multimodal analgesia regimen. The morphine consumption was selected as the primary outcome. The study hypothesis is that patients receiving parecoxib would have a lower opioid consumption.