Are knuckle bones dangerous? If not are they ok for dogs when crated?

In my opinion knuckle bones are too soft to leave with a dog unattended. They can as you have seen bite of large chunks of them and potentially swallow them causing choking or bowel obstructions. I don't have a problem giving them supervised but would not recommend leaving them when the dog is unsupervised. The only bone I would consider leaving a dog unsupervised with is a femur bone. Only the strongest chewers are likely to cause them to split and even they are hard presses to do so. Just keep and eye on them for wear and tear