This long-term extension study is designed to monitor the long-term safety, tolerability, and efficacy of treatment of SM04690 or placebo previously injected in the target knee joints of subjects with moderately to severely symptomatic osteoarthritis (OA) from a Samumed-sponsored SM04690-OA phase 2 or phase 3 study. No additional SM04690 or placebo therapy will be administered in this study.