In reply to Roadrunner5:
> I think roads are more damaging. I seriously think 2-3 years of 90-100 miles a week really banged me up.
This is kind of what I mean. Basically pummelling your knees, be it on the road, or thrashing down rough, rocky ground, damages your knees. The only cartilage damage I've had has been from overdoing it on long runs with lots of steep downhill. In the short term they always heal, but it must have a longer term effect as well.
The reason I bring it up is that I've met a few older folks (60's) in the hills recently, who say most the people their age who have been 'fell runners', now have knackered knees. Worried me somewhat since I'd like to spend many more years in the hills.