I am so sorry he hasn't improved. Have you looked into acupuncture treatments for him? Perhaps this could help - maybe his body would relax or the treatment could help correct the issues.
Here's a link to my vet's website - actually this will take you to a testimonial page & 2 different owners talk about back problems being resolved with acupuncture instead of suregery:
http://www.apvet.com/testimonials.html
His site has some good general information - you could even call him - he is a great guy and could give you some help, He has traveled the world presenting to other vets & may be able to refer you to someone in your area
Check him out and also these 2 sites -
http://www.aava.org/ or
http://www.ivas.org/
on both of these you can search for someone in your area