Interesting. I've had it done on my calf before twice, while recovering from a really bad strain that took 6 months to heal (no knee issues at that point yet). I think it may have helped with the calf a bit - certainly didn't hurt it more longterm. I just remember my calf muscle spasming like crazy when they put the needle in.
Just wondering where exactly your knee pain was coming from? (Medial/lateral?, etc.)