After giving Hunter the MRI, Sam states that Hunter's "4th cervical vertebra" is fractured, and tells Hunter he will never walk again. Any injury to cervical vertebrae 3 thru 5 would be life-threatening because the nerves that innervate the diaphragm originate there. For a spinal injury to threaten ambulation, it would have to be at least in the lower thoracic region and probably the lumbar region.