To assess the safety, tolerability and pharmacokinetics of ABT-981 in patients with osteoarthritis of the knee.

This is a phase 1, randomized, double-blind, placebo-controlled, multiple ascending dose study. Thirty-six patients with osteoarthritis of the knee will be selected to participate. Patients will be randomized to receive either ABT-981 or placebo. ABT-981 or placebo will be administered as subcutaneous (under the skin) injections in four dosing groups. Subjects will be administered subcutaneous injections of ABT-981 for up to 8 weeks.

Inclusion Criteria:

• Adult male or female, 40 to 70 years of age, inclusive.
• History of symptomatic osteoarthritis (OA) of the knee joint for at least 3 months, with typical Osteoarthritis (OA) symptoms
• Radiographic Osteoarthritis (OA) of Kellgren-Lawrence (K-L) grade 1, 2 or 3
• Patients assessment of Osteoarthritis (OA) pain intensity of the study joint is between 40 and 80 on the 0 - 100 mm VAS scale
• Other than Osteoarthritis (OA) of the study joint, patient should be in general good health

Exclusion Criteria:

• Radiographic OA of Kellgren-Lawrence grade 4 or chronic opioid user due to severe knee OA
• History of allergic reaction or significant sensitivity to any constituents of the study drug and acetominophen or history of anaphylactic reaction to any agent
• Significant trauma or surgery to the study joint within the last year or arthroscopy within 6 months, or, scheduled for major surgery to the study joint
• Diagnosis of rheumatoid arthritis, other autoimmune disorders or any arthritis other than Osteoarthritis (OA) of the knee.
• Any uncontrolled medical illness including unstable treatment or therapy.