|He has arthritis of the elbow and is on medication.|
The pet market place is very valuable to manufacturers and they are forever trying to sell more products to pet owners including cat and dog food that looks attractive to people. The cat treats are a modern phenomenon and cat owners who want to please their cat will tend to buy a packet of cat treats. Treats are packaged in a way that makes them look like sweets for people. That is the way I view them anyway.
People like to keep their cat happy and feeding them quality human food and cat treats will make a cat happy but it may also make a cat fat and flatness equates to arthritis and sometimes diabetes.
People should be aware of the possibility of arthritis in cats. When it is bad you will notice it in a cat. I remember a very old ginger tabby cat who lived outside for a very long time and he came into my mother's house for some warmth. His gait strongly indicated arthritis. It was as if he was walking sideways almost. If a cat is less mobile and has difficulty jumping up and perhaps is irritable, then he or she may have arthritis particularly if he is elderly or overweight.
If the cat does have arthritis who will be in discomfort and a good cat caretaker will not wish their cat to be in discomfort and they will want to do something about it. Perhaps a cat owner should raise the possibility of arthritis with her veterinarian if she thinks that her cat has it. The vet can then do proper diagnosis such as x-rays.
A vet will advise on treatments, of course and there are home treatments that you can read about on the Internet. As far as I am aware, there's not much you can do though and I'm sure that part of the treatment is painkillers.
The photo is by Rocky Mountain Feline Rescue on Flickr