Unlike Larry, I do have a 16 year old Maltese that is directionally deaf. This occurs more as they get older. While Amanda can her me, she cannot tell from which direction the sound is coming. It is quite obvious from the way she looks arounds for the sound. So, those that have a maltese that is getting older just be prepared, as to the possibility of that.
I agree with Larry on the knees, my Amanda has had knee surgery on both hind
legs and my little 4# Yorkie mix that is only about 4 and 1/2 has had one
knee surgery. It is very common to most small breeds. So good luck on helping you dog compensate for the deafness.