I was doing a stupid steep climb near the Hollywood sign and it suddenly felt like a knife had been stuck into my left ankle. After that I started using a compression wrap and a soft ankle brace for about a year. It is now almost 2 years from the injury and it doesn't bother me much but I still put a little athletic tape on before longish rides.
I don't know why it happened, maybe my cleat position was off a little. I've done steeper climbs since then and not had a problem.
I tweaked the other ankle on the motorcycle in the late 80s and I saw 2 doctors and got x-rays, etc. They basically said if you can walk on it, we aren't doing any surgery. Went through steroid treatments and some other crap.
For years that one would pop at night and wake me up. Still pops sometimes but it's not painful.