My left knee is a bit problematic me. If I try to run, it hurts quite a bit, and tends to to turn sideways if I make a misstep. This is because, when I was 37 years old, I decided to take up freestyle bmx riding.
I was out with Shawn, Jesse and a couple of other guys, one cold night, on the freestyle bike, riding the Tech Center. We had spent the evening attempting wall rides, bar spins, etc. The other guys, all in their teens, were pretty accomplished at street riding. But, I was just a beginner, and I was awfully proud to complete a bar spin, occasionally, without crashing out.
Eventually, we ended up in a parking garage. As we were riding down the ramp, I was standing on the rear pegs, and pulled the front wheel up, and rode a manual down the slope. Then, I over-balanced and started to fall backward. Reflexively, I stepped off of the peg to catch myself.
That was the end of that ride.
The next day, I got an MRI. The verdict: torn medial collateral, torn meniscus, torn anterior cruciate ligament...Basically, I had blown my knee out. The doctor recommended surgery, but I asked him it would be possible to do without.
"Well, as long as you keep the muscles in the leg strong enough to hold the joint together, you may be able to put it off for a few years. But I can't guarantee it," was his answer.
Thirteen years later, I still haven't had the surgery. And, I don't want to, if I can avoid it.