In mainland China, knee Osteoarthritis (OA) is the leading cause of disability in older persons. Total knee arthroplasty (TKA) is now generally regarded by orthopaedic surgeons and patients as an effective treatment for end-stage knee OA in order to relieve pain, correct joint deformity and improve the life quality of patients.However, TKA has been called as one of the most painful Orthopedics surgery due to the weight bearing characteristics of knee joint and the high demand of functional exercise within the 6-8 weeks post operation. The targeted application of selective cyclooxygenase (COX) -2 inhibitor, such as Parecoxib or Celecoxib, can significantly reduce the level of inflammatory reaction one and two days postoperation . In addition, the perioperative administration of Celecoxib can directly or indirectly relieve postoperative pain, improve articular function and eventually augment life quality of the patients . Recently, effective treatment of post-operative pain with intravenous followed by oral COX-2 specific inhibitor has been demonstrated in many post-operative pain models . Significant morphine sparing effect and reduction of opioid distressed symptoms were also observed. In China, many surgeons have accept it as a routine strategy for controlling pain post TKA to sequentially give parecoxib 40 mg intravenously twice daily for the first 3 days post surgery and then Celecoxib 200mg orally twice daily. Although satisfactory results of this combination treatment on short-term pain reduction and functional improvement has been observed in clinical practice, high quality evidence is still lacking to prove its effect on the medium or long-term functionality recovery. This study is being conducted to investigate the combination regimen with intravenous parecoxib followed by oral celecoxib for post-surgical analgesic treatment in osteoarthritis patients undergoing total knee arthroplastic (TKA) surgery. Subjects will receive double-blinded study medication consisting of parecoxib injection in analgesic doses or matching placebo followed by oral celecoxib in acute pain doses or matching placebo in a double-blinded fashion. The hypothesis is subjects treated with parecoxib/celecoxib will consume less morphine over the first 24 hours of postoperation period, achieve improved pain control over study period, a quicker return to functionality, and has less opioid adverse events than those treated with opioids alone over 6-week recovery phase.