Only certain skull bones have cavities named sinus. If we compare the cranial sinus with a bathtub full of water, the bathtub always drains through a whole located at the bottom. Were the bathtub inclined, drainage would be difficult and the remaining liquid would remain undrained.
Stagnated water would create a layer of foamy sediment that would continue to thicken along time, turning drainage more and more difficult.

Every cranial sinus -just as the bathtub- has a small opening and tube, generally located in the lower part of the cavity, that allows the mucus to drain to the outside through the nose.

Structural disorders that unbalance the sphenoid, cause an inclination of the sinus that hence prevents the full mucus drainage.
That thick overflowing mucus in an excellent stimulus for infections to appear. The body can control the infection but it cannot eliminate it.
In that way, a chronic sinusitis sets in.
Alopatic Medication attempts to kill germs, and/or drain the mucus, but it does not treat the cause: i.e. the inclination of the sinus.

When the sphenoid bone is stabilized with N.C.R., the sinus returns to its ideal position and allows a total discharge of mucus.
If a few germs remained, the immune system of the person will now be able to neutralize them; in this way, the dead germs will be discharged together with residual mucus.