They are rarely used, and seem to be a last resort if nothing else is available. If the septum is severely deviated, then it is destabilized as part of the mobilization to allow it to return to midline. To keep the reconstruction straight, a plate of additional cartilage is often used as a strut or brace as it is secured to the unstable and straightened segment. Just like a casted broken arm. Depending on where they are placedand what additional function they may provide, these struts can be called spreader grafts, septal struts, or even septal replacement grafts. In almost every case, a portion of septal cartilage is still available that can be harvested to serve this purpose. And in almost every case the "memory" of the crooked portion of cartilage can be overcome.
However, if the memory stil overpowers a cartilage strut, or no additioinal straight septal cartilage is available, then ethmoid bone is an option. For the surgeon, it's just an extension to the septoplasty, so it is convenient. More rigid too, and yet thin. So as a strut, it is an option. But truthfully things just don't usually get to that point.
One final point. This is for a crooked nose/crooked septum. The struts we describe above are in the deep tissue of the reconstruction. They do not really become part of the rhinoplasty (other than straightening things out), and therefore must be placed so that they are not palpable. That would be unnaturally rigid.
