Despite the asprin, he's probably in alot of pain!!! I don't think its so much still trying to be top dog as he's afraid of being hurt. With spinal damage like that its probably very uncomfortable for him in day to day life.
I have sciatic nerve issues myself and I know when I don't have my medication, I do NOT want to be touched. Even the lightest touch can be very very painful.
Have you considered putting him on a condroitin and glucosamine supplement to help his spine. I'm sure his hips are probably involved as well.