I understand the sequence that Amgen is suggesting of Evenity to build bone, then Prolia to "protect it" but can't understand why that would work if Prolia is an anti-resorptive drug. Does it not have the same risk of longitudinal fractures that the bisphosphonates have?

PS One study I came upon suggested that a possible reason for BRONJ is that the jaw bone sheds and replenishes bone cells faster than the major large bones of the body. Therefore the anti-resorptives mechanism of preventing the normal shedding of dead cells impacts the jaw bone differently.

PPS I don't understand why some of the osteoporosis drugs help the lumbar spine but not the femur/hip and others do the exact opposite. Or why bisphosphonates can cause longitudinal femur fractures for that matter. I've read a lot of studies but have yet to come upon an explanation for that unintended consequence.