Pea Chick leg injury please help!

[jll536]

I have a 4 day old peachick with a swollen hock joint and the leg is swollen and purple. I thought it might be a slipped tendon and I tried to roll it and while something does roll it just rolls right back and I am not even sure if it is the tendon its in the right place? It couldn't straighten its leg yesterday, but today it does straighten even though I can move something on the back of that joint. I currently have it in a little sling chair. I tried vet but they had no idea and it was a useless appointment but said if chick wasn't feeling better in a few days to cull it. What do I do?