A dog that can't do much physically can really benefit from mental stimulation in the form of training (clicker training especially; try teaching stationary tricks, body awareness skills, etc.), food dispensing toys (the Busy Buddy line is excellent, the Tricky Treat ball or Buster Cube, stuffed Kongs, Treatsticks, Nina Otennson (sp?) puzzles, etc.), maybe even some physical therapy like underwater treadmill work.
Has he seen a surgeon to discuss options other than pure pain management?
Erin, the Amazing Maggie Mae, Ziva the Wonder Dog, and Kestrel the Up and Coming
"Always keep one still, secret spot where dreams may go." - Louise Priscoll