Iv'e had knee trouble since my early 30's, I'd done several years of heavy pack carrying and several years of daily road/trail running by the time I first noticed the creaking & grinding. Since then purposely avoided the heavier packs, had physio, done specific exercises, stopped running.. Maybe those steps helped a little, perhaps a lot..?
More recently, at least 10yrs on, it had started to become a real problem, painful & unstable.. causing a few tumbles.. i'd seen various surgeons, it was time to let them have a look inside..
Here's my knee

Kneecap at the top, head of the femur below..
It's been cleaned up/ was a mess.. there were multiple problems but these pics show one common problem- grissle (in the surgeons terms lol) Broken down and loose like 'floor tiles'.
In some places there is no protective cartilage left... part of my kneecap is apparently floating around somewhere up around mid thigh...


The point is i guess.. this damage didn't take overly long to happen, even though it's taken them a while to get 'too' bad.. my advice is to take that grinding... anything that doesn't feel right as a warning. Much better still- avoid getting to that stage, there's no easy 'fix'.
From other peoples accounts and my experiences i really think now that even carrying maybe 20% of body weight, especially on hills is just too much.. I'd imagine people 20% overweight with no pack would have similar problems while still relatively young. I'm not convinced of the wisdom of heavy boots- save ankles to spite knees.. also not sure whether it is better to carry heavier weight 'less'- didn't seem to help.. My thoughts are that keeping muscle bulk, as in- carrying heavy packs several days a week most weeks of a year might be the only way to stay injury free longer (if you really need to carry them at all).
here's the before shot
