What is the scarring from a septoplasty that causes sleep apnea?

Doesn't make sense: Septoplasty does not usually cause sleep apnea which is a very comes disease that may either be central from brain) or obstructive from mechanical airway instruction usually in throat or pharynx. If your septum is sufficiently blocked to force mouth breathing, this can make a subtle sleep apnea more noticeable.

Sleep apnea: Scarring should not cause sleep apnea. If your septoplasty was successful and the septum remained straight and you still have sleep apnea then the problem is somewhere else in the airway tract.