How long do the benefits from knee gel injections last?
Any promise about how long knee gel injections last should come with a source.

How long relief lasts
OrthoInfo (AAOS) says some patients report pain relieving effects for several months following the injections. The word "some" matters, because the statement does not cover every patient and gives no fixed number of months. The same OrthoInfo (AAOS) page adds that effective injections may be repeated after a period of time, usually 6 months.
Several months is not one number
A claim such as "lasts a year" or "permanent relief" goes beyond what that OrthoInfo (AAOS) page says. The 6 month figure is a usual gap before repeating an effective injection, so it is not a guarantee of how long any one injection works for you. "Several months" is a loose phrase, and a brochure that narrows it to one tidy number has added something OrthoInfo (AAOS) does not say.
Questions to take to your appointment
OrthoInfo files this treatment under knee arthritis, so its guide to arthritis of the knee is the page to read for background. The MedlinePlus overview of knee injuries and disorders is a second neutral reference, and the WebMD pain management center gives broader pain reading. If you live in Totowa or nearby, ask the clinician how success would be judged, how long relief is realistically expected, and when a repeat would be considered. The American Academy of Pain Medicine can help you find physicians who focus on pain.
Treat the number as a range to discuss
Before you repeat a number, ask what it rests on. Here the number rests on patient reports and a usual repeat interval, so treat it as a range to discuss, not a promise.