Edge has spinal stenosis which is a filling in of the spinal column that holds the spinal cord. That can be further fucked around with via secondary injury and damage the spinal cord(a big no-no). Fusions can stabilize and hopefully prevent future injuries that can risk the spinal cord. He had the beginnings of cord injury as he complained about numb hands before matches.

Tyson actually injured his spinal cord. It's ultra-sensitive and literally every other single nerve in your body originates from it. You damage it you will damage the things at the other end as well. Tyson is in more of a use it or loses it type situation withthat kind of nerve damage. He will most likely be in much more pain and lack of use the less muscular he allows his self to get. But since he did it with such a repeated thing he cannot even begin to put his self in the same situation again as he could get the same injury again so much worse.

I get this because I am sort of in the same situation as Tyson. Spinal cord injury (mines way down the spine though) should have been able to walk again but after 2 years of intense treatment and PT, I can. Although pretty much any kind of injury I get I risk going palegic again...