There are different types of arthritis. Do you know what type he has? Normally during a flare up, ice works best first, then heat. When the flare starts to disappear, gently moving the arthritic part will help keep the joint more flexible. It is best that he be evaluated by a Rheumatologist who specializes in this type of disease, and they may have other recommendations.
There are different things available, like Rosehip, Cherry, Glucosamine &Chondroitin, Celadrin, Celaritis just to name a few.
Some people get benefit from massage, especially if the muscles go into spasm. Other people find seeing a chiropractor or osteopath helps, depending if any joints are out of alignment like in the spine and neck.
Unfortunately, there isn't a cure and it also depends on which type of arthritis he has. There are different types of arthritis, but the most common ones are osteoarthritis which is degeneration of the bones, rheumatoid which is an autoimmune disorder; Gout where uric crystals form around the joints.
It is important to have a healthy and well balanced diet with lots of fresh fruit and veg and avoid junk and processed foods.
Some people notice that their arthritis is made worse by eating certain foods or drinking things like wine, cider, coffee. Some people notice that their arthritis is much worse when the weather is about to change, like for rain or when it is cold.
It is important for your uncle to pace his day so as not to get overtired, do gentle exercises to keep mobile and rest when feeling fatigued.
It is important for him to see his doctor to find out which type of arthritis he does have. Depending on which joints are affected, and if these are severe, like the hips or knees, he may be eligible for replacement surgery.
With severe arthritic problems and because it is very debilitating, depression may be a problem too. If your uncle is depressed because of his illness, get him to speak with his doctor with regard to getting some medication to help.
If you do find anything that helps him, do let me know.
I have tried most of the things I mentioned above and I did find the Rosehip helpful with regard to feeling less pain from the inflammation, but unfortunately they are not cheap and with any of them, they need to be taken for a few months to see if you notice any change.
I understand that Alfalfa helps with arthritis as does Cholorella and Spirulina, Also, if you have access to a doctor that does accupuncture, try it, I have had it and it helps with a lot of pain and other issues as well.
If your uncle decides to take the supplements, consult with his Pharmacist first to make sure there is no interaction with his medications or medical condition(s). For example some people with breathing problems cannot take one of the above mentioned supplements, but the Pharmacist will be able to tell you or your uncle if these are safe for him to take and with any other medical conditions he has.
If he opts for accupuncture, which is also good (and I have had with great results) and may or may not be covered by insurance, make sure the person doing it is certified and uses disposable needles.