The purpose of this study is to find the optimal dose of SM04690 that can be safely given by intra-articular injection into the target knee joint of subjects with moderate to severe osteoarthritis.

Inclusion Criteria:

• Diagnosed with primary OA in target knee by American College of Rheumatology (ACR) criteria
• Screening pain criteria sufficient as assessed by WOMAC and VAS scores
• Ability to read and understand the informed consent

Exclusion Criteria:

• Women who are pregnant or lactating or child bearing potential, men must use a barrier method of contraception
• Any condition, including laboratory findings, that in the opinion of the investigator constitutes a risk or contraindication for participation in the study or that could interfere with the study objectives, conduct or evaluation
• Body mass index >40
• Major knee surgery in the target knee within 12 months prior to study or planned surgery during the study period
• History of malignancy within the last 5 years
• Participation in a clinical research trial within 12 weeks prior
• Treatment of the target knee with intra-articular steroids within 2 months or hyaluronic acid derivatives within 6 months
• Effusion of the target knee requiring aspiration within 3 months
• Use of electrotherapy or acupuncture for OA within 4 weeks
• Significant and clinically evident misalignment of the target knee
• Any known active infections
• Any chronic condition that has not been well controlled for a minimum of 3 months