The primary objective of this study is to evaluate the morphine-sparing effects of the combination treatment with Parecoxib and Celecoxib versus placebo in subjects undergoing TKA. The secondary objective is to compare the effects of the combination treatment versus placebo on pain relief, inflammation control and functional rehabilitation after TKA. Total 86 subjects per group would have 90% power in detecting 100 mg or more in mean difference of morphine use on Day 14 between the two groups, assuming a common standard deviation of 200, and a two-sided alpha level of 0.05. This would result in a total 172 subjects. In consideration of 30% drop outs, 246 subjects would be adequate for the study. All subjects who meet the study inclusion and exclusion criteria will be randomly assigned in a 1:1 ratio to either Parecoxib/Celecoxib group or placebo group. The allocation or randomization will be study site based.Data will be collected using an Electronic Data Capture (EDC) under a strict intent-to-treat methodology, i.e., all the data of any Inform Consent Form signed subjects will be included in the study database.All subjects will be recruited from 4 study centers in China. The study will consist of 3 phases: an initial screening phase which must be completed within 30 days prior to randomization; a 6-week double blind treatment phase; and a 6 week follow up phase. A two-week wash-out procedure will be required before randomization for the patients with previous use of nonsteroidal antiinflammatory drug (NSAID) or COX-2 specific inhibitors.Variables considered continuous will be presented by descriptive statistics: number, mean, standard deviation, median, minimum, and maximum; and analyzed using parametric or non-parametric ANOVA, as appropriate. Variables considered categorical will be tabulated by frequency counts and percentages; and analyzed using Chi-square test or Fisher's exact tests. All the statistical tests will be two-sided with alpha=0.05, i.e., a p value <= 0.05 would be considered statistically significant.