Weetabix:
You better off sorting that out yourself. Get Glucosomine with Condroitin supplement of good quality and take what a person you're size would need assuming it's designed for a 200lbs person.
Also take some body building protein powder like collagen which is the 'plastic' components in your knees which need to regrow. Again take proportional to your size.
This will probably take a few months. You need to keep exercise light and regular to get the movement back.
The problem with going to the doctor is they will book you in for surgery and tell you to lose weight. By the time the surgery appointment arrives you could have fixed it yourself as I described above.
This is an interesting post.
The broader message is fine. There's some mixed scientific evidence that glucosamine with or without chondroitin can help with joint pain by reducing inflammation. And he most likely needs collagen. I also agree that regular light exercise would be extremely beneficial as well.
You should not dose supplements by your weight. That is an easy way to take too much. That's not too big a deal with collagen. At this present time, there are no known complications with taking too much aside from having an unpleasant taste in your mouth, feeling stuffed, or mild stomach issues.
healthline.com/nutrition/how-much-collagen-per-day#overdoseThe same cannot be said about glucosamine. If not properly dosed, you can face a litany of severe health complications and drug interactions. These health complications can become even worse if you have conditions like diabetes, hemophilia, high blood pressure, etc.
drugs.com/mtm/chondroitin-and-glucosamine.htmlLastly, I wanted to touch on your comments about how doctors would respond to his situation. I agree they'd probably tell him to lose weight. But surgery? As someone who works in the healthcare industry, I've only seen a doctor recommend knee surgery right off the bat if someone's knee is extremely messed up (for example an old injury that didn't heal right or the cartilage has completely worn away). Surgery is the last resort - not the first.
And even if your knees get so bad the doctor recommends surgery, you can refuse treatment. I regularly interact with people in a professional and personal capacity who could use knee surgery, but refuse to get it for one reason or another. So instead, their doctor has them use walking aids, wheelchairs/scooters, and take pain medication.
I appreciate you wanting to help OP. That's a very noble thing to do. However, it's good to be cautious with certain kinds of advice as they may do more harm than good. This is why I suggest seeing a doctor. They have access to tests and scans that we don't and can better see the best way to handle a medical situation.