Dogs can have twitch like sensation in back which would look like a twitch when you pet them. This reaction could be caused by nerve irritation in the spine. Spinal nerves have branches that supply power to the muscles along the back so if these nerves are irritated by a subluxation complex a twitch may result.
Your vet will not usually pick up on this since standard vet ed does not stress nerve phys and or anatomy as animal chiropractic does.
Having your dog adjusted will fix this issue and prevent further problems such as disc problems and lameness.
call Dr Bruce at 781-337-1180 or email at indekchiropractic@gmail.com