Borax have some painkilling effect, so I would definitely say it is worth a try. It works synergistically with Iodine and magnesium.
For the cartilage; Eat gristle, bone broth, gelatine ++ large amounts of vit C. I have heard chondoitrin sulfate and glucosamine are good too. (I take glucosamine with my msm)
"From the clinical trials, it can be concluded that long-term treatment with glucosamine:
(i)reduces pain,
(ii)improves function/mobility of the joint,
(iii)reduces OA progression,
(iv)reduces risk of total joint replacement." http://www.hindawi.com/journals/ijr/2011/969012/
A combination of all mentioned I believe will have a good effect, given some time. It would probably do some good for the skin too.