limping chick

[Frithest]

I have 8 chicks that are 3 and 4 weeks old. One of the 4 week old ones, a Barnevelder (we think female), is limping. She hobbles around on short jerky steps, and seems to prefer to snuggle down on the ground than to stand. Otherwise she seems fine - eating, drinking etc. I took a good look at her feet and couldn't see anything wrong with them. Any ideas?
New to this and hoping it's nothing...
Thanks.

 

[ChickensAreSweet]

https://sites.google.com/a/poultrypedia.com/poultrypedia/poultry-podiatry
Here is a helpful page.