Hi Anne,     I can only tell you what others have said here over the years.
There are two main joint lube shots and one of them is Synvisc.   If the
joint is bone on bone,,, it does not help at all.   Some people it helped
for about 3 months,,, Some for 6 months to a year and some of them got no
help at all because their joint was too far gone.
Harv

I don't have personal experience, but my 90 year old grandmother had them a
couple of years ago, and had wonderful relief that lasted about 9 months.
She said it was totally worth it.

Kelly C.

Anne wrote and asked:

I had extremely good results -- 6 months and 9 months -- from my 2
treatments (each consisting of 3 injections) approximately 18 months apart.

The doctor switched to Hyalgan last time and it was a big DUD.

... Things are more like they are now than they ever were before.

Yep, no improvement, more pain than before.  My knee was in an advanced
state of OA; therefore, the only thing that worked for me finally was a TKR.
Nanny

I did - on my right knee - and it didn't do a thing for me.  I told them to
forget doing the left knee.  Why subject myself to something that doesn't
help me?

Sharon