They can inject the hyluronic acid into a couple different angles on the knee. You will feel the needle prick for the lydacaine to numb it, then the synvisc injection. You will feel pressure then, not pain. It should last 6 months to a year if your arthritis is mild to moderate. That is just a range as it varies from person to person. I hope and assume you are having an othopedic surgeon do this as they are skilled in this. Hope you find relief.