Chick with a broken joint (help)

[casportpony]

Does the tendon stay in the groove?

 

[Criticalicious]

Medicated feed can cause B vitamin deficiency, because it prevents cocci by not providing the Vit B that cocci needs to thrive. Personally I recommend using fermented feed and slowly build up the chicks' immune systems rather than using medicated feed, but that's a personal preference.

Earlier you asked about deworming - If the chicks are not in contact with soil or other birds, there should be no need to deworm them. If they've been raised in a brooder indoors, then they haven't likely come in contact with any sort of worms.

 

[casportpony]

Medicated feed can cause B vitamin deficiency,

Unlikely, but if it were a problem, that would be a thiamine deficiency, which does not cause the symptoms the OP is seeing.
http://www.poultrydvm.com/condition/thiamin-deficiency

 

[Criticalicious]

Thiamin is B1, so thiamin deficiency is a Vitamin B deficiency. But you're correct that it wouldn't cause these symptoms.

 

[Farm life101]

Does the tendon stay in the groove?

Yeah the tendon seems fine