This two-part study will be conducted in male and female patients, 30 - 80 years of age with painful OA of the index knee with Kellgren-Lawrence (K-L) Grade 2, 3 or 4. Part 1 - Single Ascending Dose (SAD) Phase: Up to three ascending doses of FX201 will be tested in cohorts of 5-8 patients. Each patient will only receive one injection of FX201. An independent Data Monitoring Committee (DMC) will review safety and guide the conduct of the study. Part 2 - Expansion Phase: Up to an additional 35 patients will be enrolled at each dose level reviewed by the DMC. Each patient will only receive one injection of FX201.