Background: The sliding genioplasty is a well known bony reshaping procedure of the chin. It is best recognized for increasing horizontal projection and vertically lengthening the chin. But it can also be used for many other dimensional changes changes of the chin bone such as asymmetry correction, vertical shortening as well as decreasing its width.
One of the least common uses for a sliding genioplasty is to decrease chin projection or for horizontal chin reduction. While the chin bone can be moved backward and even reduced in height at the same time, this method of chin reduction is prone to creating other aesthetic problems. While the bone can be reduced, the enveloping soft tissues remain and can become ‘redundant’ This means that a submental bulge can appear from underlying shortening and the soft tissue chin pad may develop ptosis. These are well recognized soft tissue problems with the setback sliding genioplasty.
A less recognized but equally significant potential aesthetic issue is disruption of the mandibular plane. Regardless of the actual angle of this mandibular line, it is usually straight from the angle to the chin. But when the chin bone is moved backwards this straight line becomes disrupted and a v-shaped inferior border line results. This is because the back end of the osteotomy lines moves below the existing inferior border line. Unlike the notch (inverted V) that can occur when sliding genioplasty is moved significantly forward, a setback sliding geniopasty causes the V deformity due to the bump of bone not below the line.
Case Study: This 23 year-old female had a prior history of a setback sliding genioplasty to reduce a prominent chin. This left her with a bulge under her chin and a rounded lower facial appearance. A lateral cephalometric x-ray showed that this bulge was caused by the back end of the sliding genioplasty which protruded below the inferior border of the mandible. A line could be drawn to show the location of the bone removal need to make the jawline smooth.
Under general anesthesia through a small submental incision, a reciprocating saw was used to take down the bulge along the inferior border of the jawline behind the chin. The bone was sequentially taken down until a straight line was restored from the front edge of the chin back to the jawline behind the bone bulge.
The sliding genioplasty is not usually the best chin reduction technique for a horizontally excessive chin. If done the back end of the downfractured chin segment should be removed to avoid a bulge along the lower edge of the jawline. It can also be removed secondarily through a subental incision which provides straight line access to most successfully perform it.
Highlights:
1) A setback sliding genioplasty can often cause a negative v-shaped alteration of the mandibular plane angle.
2) An inferior border shave and straightening of the mandibular plane angle can be done.
3) A shave of the anterior inferior border of the mandible is best done through a submental approach in many cases.
Dr. Barry Eppley
Indianapolis, Indiana