We have an 11 year old Dachshund who I just noticed tonight has something up with his foot. Right at the ankle, it's limp and I can feel something sliding. I am with this dog quite often, and this is the first night I've noticed anything like this. The foot is not swollen, and he appears to only be in pain/discomfort if he stands on it a certain way. Does this sound like a slipped tendon or more like a dislocated joint? How should I treat it?