I had the EXACT same thing and had surgery in Dec o7, only 9 months ago and I have the same problem. I think I have siatica now and I think mine is from sitting to much. mine is helped by walking a little and maybe that is what your dad should do. just move around a little more. this back surgery is long and very painfull and it has been very hard to recover from and I am wondering if I will ever be normal again. but for me, even just walking around a store helps.
CAT
Back surgery can take as long aa a year to resolve. But that dosn't mean something is still wrong. How long ago was the surgery? What kind of surgery did he have? How old is he? Some nerves take longer to heal from the compression. I had low back surgery and it took almost a year for me to say, ok thats better. That does not mean he will have no pain, I still have back pain and always will it's just better than before. He may need a new M.R.I. to see if something is still not right. If all is ok and the doctor, said it's ok for therapy, it may be needed to help the lingering pain. If you do go to physical therapy ask for a therapist that has a cold laser machine it helps me. First they did a surgery to just free the nerve, and it did not work so 6 months later I had fusion done, thats when I started getting better.
Hope I Help