Our BT has Luxating Patellas. Ask the vet what grade it is. We had to have the surgery on his right knee because it was a high grade (meaning the patella slips out of place very frequently). The surgery was a success, yes it was around $2500. His left kneww is a very low grade so we have not done anything to it. He only has issues rarely. There is a ton of info on Luxating Patellas on the web, it is very common in small breed dogs.