OK, now I'm going to be very silly here - opening this out to sensible discussion to.
Not being absolutely sure how the actual stifle joint works or what is 'needed' to keep it working properly, but if it is the same as our knee joint, then I do know that humans have had their kneecaps removed (although I think it is reasonably rare) and not replaced??
If little Beau has a dislocated patella, then would it not be possible, once he is a bit older and up to an op, to simply remove it? Does he actually NEED a patella to live a happy life as a pet or even doing other things if it were possible?? We need some medical knowledge here my friends - does anyone have any?
I expect the joint is a bit swollen Jenny after the vet was moving it around while trying to find to find out what was wrong in the first place.
Still saying prayers for little Beau and for Sweety too. Huge ((((HUGS)))) for you - hang in there Jenny there is always hope and we are all right there with you hoping and praying for a happy outcome.