Why must caution be used when handling a person with possible spinal cord injury?

Any damage to the spinal cord is a bad thing. Depending on the location of the damage, the victim may lose the use of their legs, loss of the use of all four limbs, or even be damaged enough to interfere with normal breathing. Any time the spine itself is injured, that injury may produce sharp edges, which can cut localized tissue, cause swelling or internal bleeding that may in turn stop blood flow to the spinal cord, as well as nearly any potential trauma. As such, if you see potention for spinal cord injury, you need to prevent as much further movement at that site as is possible. Hence the caution in moving such a victim.