• The primary outcome is the change from baseline to week 12 in the WOMAC OA Index pain and physical function subscale scores and the patient global assessment of disease activity.
  

• The secondary outcomes include: change from baseline in the daily arthritis pain intensity scores from patient diaries, WOMAC OA stiffness subscale scores, OA pain intensity VAS for index and non-index joints, and Chronic Pain Sleep Inventory scale
  

Immediate release (IR) tramadol has demonstrated efficacy in several pain conditions including, obstetrical, gynecological, orthopedic, abdominal, and oral surgery. The short elimination half-life of IR tramadol necessitates every 4-6 hour dosing to maintain optimum levels of analgesia in chronic pain. The study medication in this study is a once-daily, extended release (ER) tramadol formulation. This is a 12-week multicenter, double-blind, randomized, dose-ranging, placebo and positive-controlled, parallel-group study. For the purpose of this study, celecoxib serves as a positive control to validate the sensitivity of the model. Patients with OA functional Class I-III of the knee or hip, with moderate to severe pain are eligible for participation, if appropriate criteria are met. During a 2-7 day washout period, the use of all analgesic medications will be discontinued. Eligible patients experiencing moderate to severe pain (>= 40 mm on a 100 mm visual analog scale) in the index joint to be evaluated and who meet all other study criteria will enter the double-blind titration period. During this period, patients will be randomly assigned to receive treatment with tramadol HCl ER 100 mg, 200 mg, 300 mg, celecoxib 200 mg or placebo, once daily. During the titration period (Days 1-9) all patients will be contacted by phone every few days to ensure they do not experience unmanageable pain or unacceptable side effects. Efficacy and safety evaluations will be collected at study visits occurring at Weeks 1, 2, 3, 6, 9 and 12 or at the time of early termination. Study medication will be discontinued at Week 12 and patients will return after 1 week for a post-treatment visit (Week 13).