Our company is pursuing the wellness activities too. But I'm not ready to say the hip/knee replacements are mainly due to obesity. Again, anecdotally, the people in my extended circle really vary: maybe 2 due to obesity; a few due to accidents including falling off a roof, a motorcycle accident, and a car accident; the rest are due to participating in extreme sports after the age of 50. I mean doing things like marathons and parasailing in your 60s+.
All of that is fine, but again, in our parents or grandparents time, people in that age group weren't generally doing the risky type of sports, and if they did break a bone, they could expect to be using a cane, not getting replacement medical devices in expensive surgeries.
Finally, I'm not sure doctors would even do knee replacements for obese patients. A friend's mother was told she would have to lose 100 lbs before the doctor would operate. She did so, and only then did she have the surgery.