The sliding genioplasty is the autologous form of aesthetic chin augmentation. Even though it is a bone procedure it is subject to the same aesthetic issues as any chin implant. Patients can have aesthetic postoperative concerns about the amount of forward projection/vertical length or width as well as asymmetry issues. And just because it is a healed bone with fixation hardware on it does not mean it can not be secondarily changed or revised. It is probably fair to say that the revision risks between a sliding genioplasty or a chin implant are fairly similar. The revision difference is that a chin implant revision is easier to perform than a sliding genioplasty. So the motivation to revise it is higher.
When performing a secondary bony or sliding genioplasty the issues to consider are hardware removal, location of the secondary bone cut and what should the new bone position be. (dimensional changes)
The first important step in the surgery is exposing and removing the hardware. The ease or difficulty of hardware removal in a genioplasty depends on the type of hardware that was initially implanted and how much, if any, bony overgrowth has occurred around and/or over it. The type of hardware used can be determined by a simple panorex x-ray. The presence of bone overgrowth can only be determined by intraoperative exposure.
Most bony genioplasties today are secured by plates and screws with the far less frequent use of bicortical screws. The former is far more favorable for removal than the latter. If the threads on the screw heads of the bicortical screws are stripped this poses a major obstacle for proceeding with the revision. (fortunately I not yet encountered this issue but it is always possible)
Some bone overgrowth over the chin plate if often seen. But it can usually be removed by chipping away on it with small osteotomies to fully expose the plate for its removal.
The bone cut is almost always done through the original osteotomy site which is usually fairly evident. The greater the original horizontal advancement the more evident the bony step off is and where to make the cut with a reciprocating saw. In an advancementthe bone thickness of the chin is less than the original osteotomy cut as the advanced bone has less bone contact between the upper and lower chin segments than the original uncut bone. This means that to make the bone cut it may be a little easier than the first time although the postoperative effect on the patient (swelling and bruising) may be no different.
When it comes to establishing the new position of the bone it is easier to do more horizontal advancement or vertical lengthening than to move the chin back. A horizontal advancement can be reduced or even brought back to its original position but the soft tissues always provide some initial resistance to a 100% setback. Vertical shortening of the elongated chin requires a wedge of bone removal if the amount of reduction needed is significant. Small amounts of vertical length reduction can be achieved by bending the fixation plate upward….if there is some horizontal advancement still present.
Secondary bony genioplasties can be successfully done and will go on to heal uneventfully. They may not achieve a full bone healing as in the first genioplasty in some sections of the union of the two pieces but this is irrelevant as this is not a loaded functional bone.
Dr. Barry Eppley
World-Renowned Plastic Surgeon