Prolia has been associated with what they call insufficiency fractures. Prolia prevents the bone from renewing and can cause a buildup of weakened bone. While more commonly recognized for femur fracture, Prolia creates the situation in your whole body.
It isn't possible to say if that is what is causing the tibia fractures. In the femur the appearance of this type of fracture is a straight across break instead of a spiral break. You might look at your tibia xray.