There are a few different root causes so the solutions are a little different from one situation to another. I'll throw out a few I've heard from my contact with experts in this area and hopefully they'll do you (or someone you know) some good.

(1) Food Allergies: This is very common and when identified and the bad food(s) is/are removed, joint pain goes away. Tomato and strawberry allergies are common.

(2) Vitamin C deficiency: This can because of diet or mercury which interferes with it's action. Increased vitamin C can help in time.

(3) Aluminum exposure: This is also very common and I've heard (although not confirmed myself) can be detoxed with Malic Acid

(4) Other general causes: General swelling and/or joint degeneration. Supplements that can help:

MSM
(not recommended with those having amalgam fillings still in because this contains sulphur)

Glucosamine

Joint Health, Ayurvedic

I usually suggest the last supplement along with either of the other two (Glucosamine or MSM). They work wonders.

Hope this helps.