Since the thigh muscles tend to bunch up near the shorter femur you might have to get diapers one size larger for your child.
One thing that is crucial to remember about changing the diaper - is that because the femur is shorter and also thinner it can be (depending on the severity of the PFFD) easy to cause damage if you pull up on the ankles to change a diaper. Its almost a natural thing to want to grab the ankles and pull them toward the head and lift to slide out the old diaper and slide in the new one. DO NOT DO THAT! Instead, put your hand underneath the baby's back/butt and lift from there instead of lifting from the leg/ankles.