Near 100% of my birds are hatched in a incubator. I think My control of the environment is not as optimum as a good hen in good conditions. Besides humidity differences there is the repositioning of hatching eggs made by chicks that have already hatched causing disorientation , drowning in fluid,prolonged hatching or chicks that fail to be able to turn in the egg to create a cap to emerge from, even though they have piped through the shell and are breathing air.
Perhaps the air breathing or maturity of time causes the bones to harden, but something does, and if they have not emerged from the shell, so they have contractures. Contractures of the toes, hips, neck and legs. I do checks and crack late chicks out of the shell that are post mature. They are the ones most likely to have deformities , either temporary or permanent. The concern of most I have talked to is that it is a genetic issue and heredity is a concern.
I have never seen anything to make me consider that it is a genetic possibility. There is the big bird in a small egg with limited room to move or the opposite , too much room to move around affecting hatching and “Curley toes ” as I call them, when they point away from midline on one or both feet . I would not dismiss a good bird that has bent toes from the breeding gene pool if that is the only reason to discount them and all else is good.
I base my opinions on personal experience and substantial medical experience and anatomical knowledge gained in schooling, and practice. I am always learning something and welcome any questions, comments or support. I want all to be happy with their Araucana experience and I will do what I can to help. Enjoy. :>) edd Sheppard awesomearaucana.com ” Awesome Araucana Chicken Hatchery” since 1973