I had both knees replaced in March and was back in the saddle by May. All good, BUT my discipline is fox hunting and I prefer first flight, fast and furious. My horse is a round fellow and I ride in an old style Stubban that puts my knees out where they can (and have) been smacked by trees. It hurt before I had the knees replaced, I can only imagine the agony it would evoke now.
I thought I'd have to move back to the more sedate group. :-(.
But my polo playing daughter gave me her old KNEE PADS! These are designed for riding and taking (really hard) hits with a polo mallet or ball.
So, heads up --if you have a knee injury, surgery, or just worry about hitting things with your knees --like gates, trees, whatever, these will keep you from hurting. I think they even give the rider a better grip on the saddle.