One of my miniatures has osteoarthritis in all 4 legs. He was diagnosed with it in the back legs as a 2yr old, and front legs as a 3yr old, his was cause by other joint problems though..
He's now 7yrs and although not quite the same as he's not ridden he's still going on. He can do light walks out in hand in the summer, gets stabled, rugged and on painkillers over winter to keep him ticking over and a good joint supplement all year round. He is still perfect able to bolt round the field when he doesn't wish to be caught!
He is rarely sound though and vets has said they doubt he ever will be sound.
That is my only experiance of it and not trying to give you horror stories! lol Dinki is quite a bad case i suppose but fine for just being a expensive pet and whilst vets are happy with him we'll just keep him going...
However i did find magnets works very well for him, when he first had all his problems he had one on 24/7 all year round, now they are only in his leg wraps that he has on in the winter, really helps keep him going. (and when he can drag me into his stable at night.... i don't see much wrong with him at the moment! lol)
RIP Halo - 1998 - 2006. Miss you always.
My little
horrors darlings.