That looks like the hock, so possibly a slipped tendon. Here is some reading about treating one:
https://www.chickenheavenonearth.com/slipped-tendon-in-baby-chicks-leg-what-you-can-do-to-help-chicken-heaven-on-earth.html...
Slipped tendons in chicks can also be acommon. The hock joint may become swollen or raw. Pictures can help. I would start some poultry vitamins that contain riboflavin (vitamin B 2.) Poultry Cell has riboflavin.
Pictures will definitely help. Here are some links with pictures of leg bone deformities, and if you see anything that looks like what you are seeing, let us know:
http://www.thepoultrysite.com/articles/1051/leg-health-in-large-broilers/...