This is an interesting article on crooked keels that someone posted on the Langshan FB page. I'm dealing with crooked keels in my Pita Pinta flock and culling hard to try to get rid of it. According to the studies in this article, I should consider giving them Vitamin D and maybe change their roosts.
http://www.ksre.ksu.edu/historicpublications/Pubs/STB044.PDF
http://www.ksre.ksu.edu/historicpublications/Pubs/STB044.PDF