We are all constantly learning. It's not your fault. I found this and it may give you some helpful info. At least, I hope so:
Many toy dogs live their whole lives with luxating patellas and are never lame. A "luxating patella" would be best described as a "trick knee" which can move out of place if injured by jumping or walking in a hole in the ground, etc. Toy dogs are prone to this because of their diminutive size. No matter how firm the knees seem as puppies, toy dogs are liable to injure their knees depending on the degree of luxation. The grooves in the knee where the knee fits is sometimes shallow and the knees can be very wobbly. Most breeders do try to breed away from this. The taller more fine-boned dogs seem to be more prone to this kind of injury.
Sometimes, if the knee pops out and stretches the ligaments that hold it in place, it becomes a chronic problem and the dog becomes lame and in this case, the first treatment would be to keep the dog crated for a week or two and supervise the activity -- no jumping from furniture and up and down behind a gate on a slippery floor, etc. Also in conjunction with that the dog should be given prednisolone to take down the inflammation. My Vet suggests 1/2 of 5 mg tablet 2 times a day for three days, 1/2 of 5 mg tablet one time per day for three days and then 1/2 of 5 mg tablet every other day four times during the crating convalescing time. Check with your Vet for the dosage and this prescription medication. Usually this period of rest will be all that is necessary to correct the situation.
Surgery is very seldom the answer and should only be done by an orthopedic surgeon if the dog is lame. My vet says that if surgery is done for a luxating patella on a dog that is not lame, he can guarantee you that THAT dog will have problems with arthritis from the surgery five years down the line. Many show dogs have finished their title with at least one luxating patella.
http://www.shooterdog.com/alexfaq2.htm