That photo looks a tiny bit like slipped tendons. Check out this thread and search for slipped tendons for chicks and see if you can diagnose it.
https://www.backyardchickens.com/th...s-rehabbed-these-babies-successfully.1520246/
https://www.backyardchickens.com/th...s-rehabbed-these-babies-successfully.1520246/