you can massage it back in place here is a pic of it so you can see what it is and it is the patella you are trying to move back in position on the knee cap when it pops out of joint you need to massage back into place - hope this helps - If the groove is not deep enough it will pop in and out. You can use cosequin as joint supplement if it keeps happening i would recommend giving this to your yorkie
DEE DEE :: stifleanatomy.gif picture by dwerten - Photobucket