The nose is comprised of 2 nasal airways which lie side by side like 2 rooms with a common wall & 2 outer walls. The doorways into the rooms are analogous to the nostrils. The outer walls are made of bone & nasal lining(mucosa). The common wall contains cartilage in its center (nasal septum) covered on both right & left sides with nasal lining (mucosa). The cartilage is analogous to plaster or gyproc in a wall & the lining is analogous to wallpaper. When the common wall is crooked(deviated septum) it can block the free flow of air through the nose & block drainage of the sinuses which drain through the outer walls into the nose. When blocked the sinuses collect mucous & may become infected.
Most people have some degree of septal deviation but it is not symptomatic. The deviation arises from trauma after birth or can be due to trauma during passage down the birth canal. The deviation is classified as oblique, C-shaped or S-shaped & the surgical treatment is based on which class is present. The oblique is easiest to
treat as only a bottom strip of cartilage is removed (analogous to the baseboard of a common wall in the example given). The cartilage can then be swung into the midline. C- & S-shaped are more difficult to treat requiring removal of a square of cartilage from the center of the wall while leaving the lining in place & an outer L-shaped rim of cartilage. In some cases internal splints of cartilage have to be placed to keep the cartilage straight as cartilage has some degree of memory & tends to go back to its original shape.
In some cases additional drainage procedures from the sinuses may be required as the opening of the sinuses into the nose is faulty as well.