To compare the safety and efficacy of celecoxib versus placebo in the treatment of patients with knee osteoarthritis who were unresponsive to treatment with prescription strength naproxen and ibuprofen or who could not tolerate prescription strength naproxen and ibuprofen

Inclusion criteria:

• OA of the knee in flare state at baseline visit and functional capacity class of I-III
• Failed adequate trials of both naproxen and ibuprofen (prescription strength) within the past 5 years due to lack of efficacy, tolerability or both; duration of prescription strength ibuprofen and naproxen must have been a minimum of 2 weeks for each drug at the respective recommended doses if failure was due to lack of efficacy, and for any duration if failure was due to lack of tolerability

Exclusion criteria:

• Inflammatory arthritis or gout/pseudo-gout with acute flare within the past 2 years (subjects with fibrositis or fibromyalgia will not be excluded)
• Received acetaminophen within 24 hours of baseline visit
• Use of mobility assisting device for less than six weeks prior to study screening or use of a walker
• History of gastrointestinal (GI) perforation, obstruction, or bleeding
• Diagnosed or treated for GI ulcer within 60 days prior to first dose of study medication
• Recieved corticosteroids or hyaluronic acid within certain timeframe before study