What exactly did she tell you??
I took Mr. Biggs in for his yearly shots/check-up and the vet told us that his two back knees popped out of place. He said it's fairly common in smaller dogs. He also said that because of that he is prone to arthritis. He reccomended surgery, but that if it wasn't bothering him, then it could wait. He said once it becomes a problem that then surgery is a option.
This was my first time going to this vet....my other vet never told me any of this. The new vet seemed shocked that i was never told this before. Part of me wonders if it's just them trying to get money out of you. Even the tech tried to get me to have him neutered telling me that he would live so much longer, she even tried to change my mind about what flea/heartworm prevention to get and practically forced it on me.
If he doesn't seem to be btohered by his knees, I'd just keep an eye on it incase you notice him ever in pain.