One more thing about fixed gear bikes and knees...

First get one of those old Samsonite suitcases and fill it up with heavy junk.

Find a framer's hammer, one of those heavy, mean puppies.

Put your hand on the table.

Smash the daylights out of your hand with the framer's hammer.

Go over to the Samsonite suitcase and try to pick it up with your smashed hand.

"Ouch!"

Yes, "ouch!"

Someone might say you have too much stuff in your suitcase, like, they might say you have too high a gear on your fixie.

Yes, picking up heavy suit cases hurts.

It hurts less if you take all the stuff out of the suitcase (get a lower gear).

Better yet, stop smashing your hand with a framer's hammer.

If your knee hurts on a fixie, you injured your knee before you ever got on the bike.

Gearing down might help.

But you need to heal your knee and stop injuring your knee.

The fixie didn't cause your knee pain anymore than picking up a suitcase hurt your hand after you smashed it with a framer's hammer.