It is possible for rods and screws to break, but I have never heard of breakage causing a pedicle screw to be pushed (or screwed) through the vertebral body into the great vessels (vena cava, aorta, etc.) or intestines. The screws are much more likely to be pulled out of the spine then push through the spine. The screws can break inside of the vertebral body. I hope this helps answer your questions. Good Luck!