A sliding genioplasty is a well known method of chin augmentation. It is often compared to a chin implant when considering aesthetic changes to the chin as a more natural alternative. But the reality is that its indications for use are somewhat different than an onlay bony augmentation. It is often only used when the amount of chin augmentation is considerable, certain dimensional chin changes are needed (vertical lengthening, width narrowing) or some functional improvement is desired. (e.g., lower lip incompetence, mentalis muscle hyperactivity, sleep apnea)
When a sliding genioplasty is performed, unlike a chin implant augmentation, it creates a sharp step-off between the upper fixed and lower repositioned bony edges. Essentially it is a stair-step effect whose degree and angulation depend on what type of bony movement is done. The bigger the horizontal advancement or the amount of vertical lengthening that is done, the more significant this step-off is.
The step-off in a sliding genioplasty can be more than an anatomic observation. This bony area provides support to the overlying upper soft tissue chin pad and part of the labiomental fold or labiomental sulcus. While it does not provide exclusive support to the labiomental fold, a significant bony step-off from a sliding genioplasty can make it deeper or more indented.
Filling in the sliding genioplasty step-off can be a useful aesthetic maneuver to help make for a more natural chin shape. Numerous alloplastic materials have been advocated for this induced bony contour defect from silicone and Medpor implants to even bone grafts. But getting a good adaptation and adequate fill can be challenging not to mention the alloplastic nature of some of these graft choices.
One of the best and most historic bony replacement/augmentation methods is hydroxyapatite (HA) granules. Composed of either resorbable or non-resorbable calcium phosphate materials, their granular form allows for a complete fill of a bony defect. Packing granules into a bony defect creates a porous graft that allows for extensive vascular ingrowth and some degree of bony ingrowth or even bone replacement. This is an ideal material for the step-off of a sliding genioplasty which can either be used as a simple fill in or can be packed into an overfilled shape for more of a soft tissue augmentation effect.
While not every bony genioplasty step-off needs to be filled in or augmented, large chin movements can prevent adverse overlying soft tissue effects.
Dr. Barry Eppley
Indianapolis, Indiana