To evaluate the safety and efficacy of ABT-652 in combination with a Non-steroidal Anti-inflammatory Drug (NSAID) compared to NSAID alone in adults with osteoarthritis (OA) of the knee.

This is a randomized withdrawal design study, containing a 4 week open-label period followed by a 6 week double-blind period. The total treatment period will be 10 weeks.

Inclusion Criteria:

• History of osteoarthritis (OA) of the knee joint and meeting American College of Rheumatology (ACR) Clinical and Radiographic criteria,
• Currently taking nonsteroidal anti-inflammatory drugs (NSAIDs) and still experiencing pain as per the protocol requirements.
• Willing to washout of analgesics and to follow treatment plan, visit schedules and study procedures.

Exclusion Criteria:

• Diagnosis of rheumatoid arthritis, autoimmune disorder, arthritis other than osteoarthritis involving the study joint, or other painful syndrome that could interfere with the assessment of pain at the study joint
• Any cardiac, respiratory, neurological, psychiatric disorder or any other medical condition or illness that is not well controlled with treatment