A spinal cord injury usually begins with a sudden, traumatic blow to the spine that fractures or dislocates vertebrae. The damage begins at the moment of injury when displaced bone fragments, disc material, or ligaments bruise or tear into spinal cord tissue. Most injuries to the spinal cord don’t completely sever it.

https://www.ninds.nih.gov/Disorders/All-Disorders/Spinal-Cord-Injury-Information-Page