As I advised you in the past, I would never do surgery on an adult pup with luxating patellas that are not causing issues with him walking. I don't recall how old Thumper is. A lot of vets advise this surgery and sadly it is what I believe a money maker for them.... the problem with doing it in an adult is that the wear and tear on the cruciate ligament has already occurred. If they tear that ligament down the road, the poor pup is back in having knee surgery and it is very expensive on top of it. Young pups under the age of 2 is differnt...then if you repair the LP it is less likely you will have a tear of the CCL down the road. Of course it CAN happen, but less likely since the knee is not popping in and out.
Here is a link to the advice I gave you previously:
http://www.yorkietalk.com/forums/4739478-post6.html