Is the muscled atrophy in the leg with the luxating patella? if so, thats very common because she doesn't put as much pressure on that leg then she does the "good" leg. My yorkie has bilateral LPs which has caused her to be more muscular in her front end so help support the weakness in her hind end. Most people wouldn't notice this unless it was pointed out.
Physical therapy would help build up muscle mass, especially swimming because she won't have to put any pressure on her legs but still be able to use them all equally.
__________________ Kellie  and  Morgan |