Chin asymmetries are not rare and can occur by a variety of developmental issues. The lower jaw can have developed with two different sized rami which becomes evident at the most anterior projecting point of the chin with its deviation to the shorter ramus side. The jawline behind the chin may be symmetric but the chin itself has developed two different sized sides. How each of these types of chin asymmetry are treated will differ.
A good way to think about chin asymmetry is to view the lower jaw as an equilateral triangle, the chin is in the midline at the top of the triangle and the jaw angles at the base of the triangle. When the sides of the triangle are uneven the chin will deviate to the shorter side. In these types of chin asymmetries the ideal treatment is to straighten out the jaw behind the chin with osteotomies which will bring the chin to the midline.
But if one only wants to treat the chin asymmetry alone the triangle concept can also be useful. Using the facial midline s a vertical line the axis of the chin deviation is marked. The intersection of these two lines creates an angle. By connecting the two lines at the bottom of the chin by a horizontal line a triangle is created.
This angle and/or triangle creates the exact amount an opening wedge osteotomy needs to be done to being the chin back to the midline. Replicating the opening angle creates the bony gap needed to swing the chin back to the midline. Once plated the created bone gap is filled with tissue bank bone chips.
The opening wedge bony genioplasty is a common technique for chin asymmetry correction. The concept is straightforward with a horizontal bone cut and a shift/tilt of the mobilized chin segment back to the midline by creating a bone gap. How much to open up the bone gap is traditionally done by eyeballing the midline position. One make this estimate more precise by transferring the vertical angle of divergence as measured externally to that of the internal bone.
Dr. Barry Eppley
Indianapolis, Indiana