I've had Starship for 3 months now and when I got him they told me the knee condition is purely cosmetic, it doesn't bother him at all, it just looks weird. I had a vet look at it as well and he told me the same thing.
If you follow the link you can see what I mean with "weird" and that it really doesn't get in his way. I was informed to pay special attention to warming him up and cooling him down, he gets supplements for arthritis and I hose down his knee a few times a week.
When he was still racing they had to give him shots in his knees about every 2 years, he would not want to trot anymore, that's how he shows he's hurting, he goes straight from walk to canter.
I try to tell myself that if it aint broke, don't fix it, but it just bothers me. Does anybody have experience with this, is there anything I can do?