This hansom cavalier king charles spaniel has got very weak in his hind legs. Its most likely this is actually neuroligical and not straight forward arthritis.
But its ok. We can still help. We have set up mum with a sensible home excercise regime to get those nerves firing and getting better communication in the legs again. This will help him gain confidence and strength. 

Good luck with the home regime mum amd keep up the good work Arthur. Your trying so hard.