Hi there --- my girl suffers from severe arthritis in her spine.... we take her for laser therapy once a month which helps keep the spine 'loose' and lessent the pressure. We also have her on a neurilogical drug, which may or may not work for your baby --- Gabapetin, which stops the receptors from telling her she is in pain. She knows her limits, but she can walk, play, run, do steps etc.
As for weight control, we use green beans as a filler. So, if we need her to lose a few pounds, we cut her kibble to 3/4 cup and make the rest 1/4 cup frozen green beans. We have to keep Banks at or below 60 lbs, so once I know she is over, I do this for a week and she is back where she needs to be. Usually have to do it maybe once a year or so.