Given Yo's ability to be Yo, I wonder if she broke her coccyx during his birth. The coccyx is the very bottom portion of the spine, often known as the tailbone. That could easily be spun to be said that her spine was broken during childbirth.
http://www.webmd.com/fitness-exercise/tailbone-coccyx-injury
Most tailbone injuries are caused by trauma to the coccyx area:
A fall onto the tailbone in the seated position, usually against a hard surface, is the most common cause of coccyx injuries.
A direct blow to the tailbone, such as those that occur during contact sports, can injure the coccyx.
The coccyx can be injured or fractured during childbirth.
Repetitive straining or friction against the coccyx (as happens in bicycling or rowing) can injure the coccyx.
Sometimes, the cause of coccyx injuries is unknown.
Less common causes of coccyx injuries include bone spurs, compression of nerve roots, injuries to other parts of the spine, local infections, and tumors.
Just a thought.