A Study to Evaluate the Safety, Tolerability and Pharmacokinetics of Multiple Subcutaneous Injections of ABT-981 in Patients With Osteoarthritis of the Knee

* 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

* 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.