The splayed leg should be caused by the fact that there is nothing in the nest box when the chicken hatches or the sawdust (wood shavings for small animals) is not thick enough. During the growth process, chicks often slip when they are unstable in the nest box, and after a long time, they form splayed legs.
The prevention is very simple, 1, the nest box is covered with sawdust with a thickness of one centimeter, and 2, two layers of plastic mats for packaging fruits (to be fixed in the nest box), both of which I have used and are very easy to use.