Legg Perthes and Luxating Patella are two different issues although both have to do with the bones in the back legs. Legg Perthes is a condition that involves the hips and the long bone called the femur. Luxating Patella involves the knees. The ligament and/or the grooves in the knee socket do not hold the bone in place causing it to pop out. Either way, you really need to take her be evaluated. I would also be in contact with your breeder.
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