ok all i can say is be careful.i hurt my knee arseing about on a bmx,whilst pissed, over ten years ago.i had no idea id damadged it as i was a tenager and when your a teenager you indestructable..right? any how it is now only just right ten years later.i ignored the problems for years but i basically damaged or tore the cartilage early on.i ignore it and bits broke off and then jambed into other bits and did more damage over the years.i eventually had a keyhole op, which i really had to fight for.they removed four pices of cartiage,each the size of half a pea.might not sound that big but the thing is cartilage doesnt really regenerate.ever.
i was so much better after wards but it has played up since and i nearly ended up having the op again, but the specialish did loads of x rays and said it wouldnt help.this was the point where i suggested that i wanted to go from commuting 4 miles a day to getting into mountain biking, all be it slowly and steadily.both the specialist and my gp said they did not recommend it as it would put strain on my knee and make matters worse.I went against there judgement, bought a full sus bike and started riding increasingly long distances.8miles, 10,12 16,20,22. then i joinded my local club and each week i go out for a 25-35 mile night ride, sometimes twice in a week. and the thing is the exercise has transformed my knee.the muscle defeniton etc is so much better it support the joint and i hardly ever get grief from it.but i built it all up slowly.
in anut shell, fight for the best treatment you can get and never presume your ok.once serious damage is done its very hard to recover.