Whenever my family and I touch our 6 year old Maltese Shitzu back leg he yelps in pain? Walks with a limp and from time to time he walks on his right leg only because of it. He has no other health problems and this is very out of the blue? We went to the vet a day after it started (23rd/12th) and she thinks it’s something to do with his muscle but not 100% sure. What do you think it is and what would be the cost?