• 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: the change from baseline in the daily arthritis pain intensity scores from patient diaries; WOMAC OA stiffness subscale score, 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 tramadol IR necessitates every 4-6 hour dosing to maintain optimal levels of analgesia in chronic pain. The study medication in this study is a once-daily, extended-release tramadol formulation. This is a 12-week multi-center, double-blind, randomized, dose-ranging, parallel-group, fixed-dose, placebo-controlled study. Patients with OA Functional Class I-III of the knee or hip (index joint) 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 in a 2-week,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, 400 mg or placebo, once a day. Patients will be titrated to their assigned dose between study days 1 - 15 and will continue at that dose for the remainder of the study (Week 12). Efficacy and safety evaluations will be collected at study visits occurring at Weeks 1, 2, 3, 6, 9 and 12 or at early termination. Study medication will be discontinued at Week 12 and patients will return after 1 week for a post-treatment visit (Week 13). Patients with unmanageable pain or with unacceptable side effects will be discontinued from the study and alternate analgesic therapy initiated, as appropriate.