Slipped knee caps in dogs

[Klynne]

I have to take my pomeranian to the vet. She is about a year and a half old. I am pretty sure she has a slipped knee cap (luxating patella) Over the past couple of months, when she has chased a ball, she yips, then favors her back leg. But after rest she is o.k. Tonight, I took her on a walk and she was fine. My boyfriend came home, and took her on a brief stroll, and she started limping. I felt her leg, and could feel a little bulge. I tried to massage it for her, and she tolerated it for awhile, but then got pissy. I understand, it must hurt. I was trying to pop her knee back in place, but I am no doctor. I read stuff on the internet, and they recommend glucosamine. So, have any of you dealt with this sort of thing with your dogs? I am calling the first thing in the morning to get her an appointment.