Background: The concept of the sliding genioplasty is fairly straightforward. Cut the chin bone, move it forward and put a plate on it to hold it into place. While this is true there are numerous aesthetic and technical considerations involved that can make for a successful or unsuccessful aesthetic outcome. Such factors include what dimensional chin bone changes are needed, how to satisfactorily hold the bone in place, does the bony step off need to be filled in and does any submental fullness need to be reduced.
While moving the chin bone after it has been cut is uncomplicated the key question is how much to move it forward. There is no exact method as to how to do so unlike cephalometric assessment of facial bone movements. The most common method in my experience is to use a vertical line dropped down from the lower lip as a reference. (I didn’t say that it where anyone’s chin should be) The most anterior projection of the soft tissue chin pad (pogonion) is then measured out to this line and this number serves as the maximum amount of forward bony movement needed. Using this number as a point of reference and looking at computer imaging of different chin augmentation amounts (behind this line, at this line and past this line) this provides a good estimate of the amount of forward movement needed that best suits the patient.
But what this method does not account for very well is the vertical element of the chin augmentation. What the vertical component of the chin augmentation can be imaged it can not take into account what happens with forward chin movement. As the chin comes forward it recruits tissue from the immediate submental area and naturally adds some length. This effect becomes more significant the greater the amount the chin is moved forward. This is magnified by a natural tendency in the sliding genioplasty to inadvertently create a gap opening in bringing the chin forward. This also will create some inadvertent vertical length. Considering these lengthening effects is especially important in larger double digit sliding genioplasty movements. In the vertically short chin these dual effects alone will usually create all the length that is needed without deliberately doing so. If the chin has adequate vcrtical length already then the chin should be shortened as it comes forward. This is most easily done by bending the 90 degree plate so it that it moves the chin up a bit as it comes forward.,
Case Study: This male sought chin augmenmtation with a horizontally and vertically short chin shape. His horizontally short chin was significant. Unlike many short chins, where it can actually have an increased vertical length due to a high mandibular plane angle, his chin was vertically short due to a flatter mandibular plane angle. The measured distance between his soft tissue pogonion and the vertical lip line was 12mms.
Under general anesthesia and through an intraoral approach a sliding genioplasty was performed with a 12mm movement. The titanium step plate was kept at 90 degrees without any deliberate effort to lengthen the chin.
The large bony step was grafts with 5ccs of rehydrated cadaveric bone chips. A musculomucosal layered closure was done over the grafted step.
The immediate intraoperative result showed the chin augmentation effect.
When seen the next day in the upright position the full effect of the sliding genioplasty could be seen.
One of the benefits of inferior chin pad roll out when combined with lengthening the jawline and stretching out the attached neck muscles is the improvement of any submental fullness. It may not completely eliminate the fullness but a definite improvement is seen.
Key Points:
1) Double digit sliding genioplasty movements can be achieved regardless of the thickness of the chin bone.
2) With significant advancements in very short chins the advanced bone usually needs to be vertically shortened as it is brought forward to prevent excessive chin elongation.
3) It is usually advantageous to bone graft the large sliding genioplasty movement to prevent soft tissue contracture into the new bony defect.
Dr. Barry Eppley
World-Renowned Plastic Surgeon