This is just a guess, but the possibility of surgical adhesions comes to mind. Scarring:
Scar tissue caused by the surgery, wrapping itself around the nerves in the spinal canal.
If this is the case, a homeopathic remedy that dissolves scar tissue would be in order.
The remedy Thios. comes to mind. Why not order a 12C of that and take it twice a day for a month and see if you improve. I hear that yoga also helps in stretching out these scars so that they loosen up and free the nerves.

This is my best guess on what has happened. Good luck!

Snoopy