slinkycat, have you ever had anything done about it? Problem is it is often put down to 'Jack Russells often do that' but in fact it can be operated on and in some breeds we have a test before breeding to ascertain the status of the patella so it is not passed on to puppies. There is something called the Putnam Test where the level of luxation is graded and 0 is ok, 1 is where it pops out if manipulated, 2 is where is often pops out but can be put back, 3 is where it stays out and 4 is where it cannot be put back. Thats a very simplistic explanation and you can google it for more information. This is something that pedigree dog breeders check for whereas the 'designer' dog breeders and backyard breeders would probably not take any notice of and breed from them anyway, yet we are the ones who get castigated for breeding unhealthy dogs!