To compare the efficacy and safety of celecoxib versus ibuprofen in subjects with osteoarthritis (OA) of the knee.

Inclusion Criteria:

• Aged >= 40 years old
• Diagnosed with OA of the knee according to the American College of Rheumatology and OA in flare state at baseline visit
• Functional capacity class of I-III

Exclusion Criteria:

• Inflammatory arthritis or gout or pseudo-gout with acute flare within the past 2 years (subjects with fibrositis or fibromyalgia will not be excluded)
• Acute joint trauma at index joint within the past 3 months with active symptoms
• Score of >=20 on PHQ-9 or score of >=1 on PHQ-9 item i
• Use of mobility assisting device for <6 weeks or use of walker