Maybe CalPiggy was a runner? I've had friends in their 40's thru 70's who were not obese but athletic that needed multiple knee/hip replacements.
As a recipient of two titanium-alloy hips before the age of 45, I can assure everyone that there is no straight-line causation between either obesity or physical activity and joints failing. Either of those
may be the cause in
some cases, but certainly not all.
I'm hardly Olympic athlete lithe, but I'm not exactly sucking-down-sodas-on-food-stamps obese, either. I have a 40 waist, and have since I was about 33. That came about from too much time sitting behind a desk and a few too many beers at the end of the work day. But I've never broken 225, and I was 187 at the end of my senior year of high school, so it's not like I packed on 150 lbs. or something. I was indeed quite athletic through high school and college, combined with a lot of just general hard work during and after both, but while I basically blew out my knees (through injury) playing football in middle school and early high school, it was actually my hips that went bad and wound up putting me in a wheelchair for a while.
My hips went bad because of a condition called avascular necrosis (AVN), a fancy term for saying that the blood stopped flowing to the tops of my femurs and they died off, along with the supporting cartilage, over the course of a couple of years, and eventually my femurs were grinding into my pelvis, bone-on-bone. AVN has a whole host of causes, and some are never really known, but some are just bad genes, which is what it was in my case: I took a bad draw in the genetic poker game. It wasn't running bases or sprinting down the sideline or running marathons or even just busting my ass out in the yard that caused my hips to go. It was good, old fashioned bad luck. And it happens to a surprisingly large number of orthopedic patients of all ages.
I can't say what this particular DUmmie's cause was for the need for joint replacement, but I can safely say that it's entirely likely that no one else can, either.