Many sliding genioplasty procedures involve a forward movement of the chin bone. As a result this creates a classic bony step off as evidenced by the commonly used stair step bone plate use to secure it into its new position. While effective this creates an unnatural shape to the outer cortical surface of the bone which tis normally more of a convex shape and not a 90 degree bone shape.
In small forward movements the bony step may not have any aesthetic consequences. But as the movements become more substantial (8 to 10mms), this very visible chin contour ‘deformity’ may have some undesired effects. While the lower end of the soft tissue chin pad moves forward with the bone, the upper part of it collapses back onto the bony step will lack of underlying support. This will deepen he labiomental fold and may also negatively impact lower lip support.
As a result a preventative maneuver is to contour the bony step off can have a beneficial aesthetic effect. What to place in the step off can be debated from implants to actual bone grafts harvested from the patient. But no patient wants a bone graft harvested for its aesthetic benefits and the use of an implant increases the infection risk. What I have found most useful is to graft this chin area but not with autologous bone.
Allogeneic corticocancellous bone chips is a good option for the chin defect. It is tissue back or cadaveric graft material that is available is small chip sizes. I mix the se bone chips with antibiotic powder, which when wetted, creates a moldable slurry. The shape of the chin step allows for a good graft volume to be placed and held securely in place. Mentalis muscle is closed over it and complete bony overgrowth of the fixation plate should be expected within six months after surgery.
Restoration of the more natural shape of the bony chin at the time of a sliding genioplasty is not always necessary. But in large forward or vertical lengthening movements it can have some aesthetic benefits in addition to creating faster healing of the osteotomy.
Dr. Barry Eppley