Almost all the pressure of the hold lies in the spine, from the neck all the down to the lumbar part.
As you can see in the picture, the spine has natural curves to it. The view in the picture above would be how the spine would be with an opponent who is laying face down.
Try and picture in your head a person sitting on the lower half of the spine, and pulling up on the upper half.
If Full Force was Applied
When the spine is pulled in the direction, the vertebrae in the thoracic (middle) section will begin to pull away from each other.
Between each vertebra lies discs that are used as cushions and shock absorbers. These discs will begin to pull away from the vertebra they are attached to.
As the person pulls back more on the spine, the discs will start to herniate and rupture.
While the discs are rupturing and vertebrae are being pulled apart, nerves that attach to each vertebra will begin to be stretched. Once they reach the point of not being able to stretch any further, they will begin to tear. Once nerves are torn, they almost never can be repaired.
There would also be a chance for parts of the vertebra in the cervical (neck) spine to be fractured. These vertebrae are the smallest in the spine, and are fairly easy to break when the neck is pulled backwards into a position that goes beyond the normal range of motion.
Many of these potential injuries would be affected by a number of factors—the first one being the flexibility of the person trapped in the hold.
If a person has a natural flexibility, it allows their spine to bend more, allowing fewer chances of injury.
The second factor is the strength of the person applying the hold.
Because the person is pulling back on the head of the opponent, upper body strength would dictate how far they are able to pull back on the person.
The stronger they are, the further back they can bend the spine and the more damage they can do.
Whenever the spine is involved, there is always potential for career and life-altering injuries.
As I said earlier, if nerves become damaged, they almost never can be repaired. Many nerves attach at various points on the spine. These nerves affect different parts on the body. Depending on which nerves are injured the outcome could be serious, or not really noticeable.