All I know about joint ill is that it's septic arthritis. Can she ask her vet? How has he done so far?
ONce she started treating him and he got over it he hasn't been lame since. I don't know if she has asked the vet about long term effects. I'd say no. She doesn't like to hear things like that:). Just like she didn't like hearing about iodining the umbilical cord, or getting a pregnant mare off fescue. The year after she had this foal, she had another that she left the mare on fescue, because "there isn't that much out there". She had to bottle feed it, and it died at about 4 months. I think it's immune system wasn't strong. Just my guess. He got a cold, and died.
She is now a believer in iodine and no fescue:). Altho she hasn't breed anything since then either.
Becky
If it's like people though, once you develop arthritis you have arthritis. There are things you can do to help with mobility and discomfort but if the joint damaged besides surgery you can't cure it.