Swollen Hock

[kth1025]

I have a show steer that has a swollen hock for about 2 weeks now and is limping on it. I have not idea how it happened haven't taken him anywhere and nothing in or around his pen that could of done this. Just not sure what happened. Any suggestions as what to do. Vet seems to think he has gone lame and can't explain really what is wrong blames it on high protein feed. Which he is only on 13%. Giving him RVI shots that really seems to make him perk up but that isn't a solution to the problem. Any suggestions?