Horizontal and Vertical Lengthening Bony Genioplasty
The ability to make this simultaneous two-dimensional chin augmentation change is an historic advantage of a bony genioplasty over that of an implant. While some argue that a chin implant can be positioned lower on the bone to create this effect, this effect is limited and such implant positioning is potentially unstable.
How much vertical elongation and horizontal projection can be combined and still maintain some bone contact between the upper and lower bone segments are not absolute numbers. Usually the horizontal movement is greater than the amount of vertical lengthening needed in most patients and this does not pose any restrictions from so doing.
As the chin is vertically lengthened the labiomental fold does not get deeper or not as much. In some cases of a significantly short vertical chin the labiomental fold may get less deep as the compressed soft tissue chin pad is forced lower and expanded from the vertical bone movement.
Vertical Lengthening Bony Genioplasty
The chin can also undergo an isolated vertical lengthening which is indicated when the lower third of the face is disproportionally deficient even if adequate chin projection exists. Just like cutting the chin bone and moving it forward, it can also be cut and vertically lengthened. Also known as an opening wedge bony genioplasty, the chin is opened with the back ends of the osteotomy line acting like a hinge. It is held in its lowered position by a small spanning titanium plate with screws. While it can be vertically lengthened by any amount, it usually takes up to 8 to 10mms to see a significant external chin lengthening change.
Since this type of facial osteotomy exposes the marrow space of the chin bone on both sides of the bone cut and the downfractured chin segment is well vascularized through the maintenance of inferior soft tissue attachments, it is likely some bone healing would naturally occur in the gap space. But with a bony gap that may be up to 10mms, I prefer to graft that gap to allow for maximal bone healing between the superior and inferior bony chin segments. This is most needed in the central area where the gap distance is the greatest. The size of the gap becomes less at the sides of the chin where it tapers down to actual contact between the upper and lower segments. Graft options include tissue bank bone and synthetic hydroxyapatite compositions.
A pure vertical lengthening genioplasty is very effective at chin lengthening and is the ‘least’ traumatic of all bony chin movements since the bone segment is merely opened to create the dimensional change.
Vertical Shortening Bony Genioplasty
A vertically long chin, just like a vertically short chin, can be changed by an interpositional wedge technique. In the long chin a wedge of bone between the upper and lower portions of the chin is removed through its middle section. The bone cuts must be carefully planned to stay well below the canine tooth roots and the mental nerve foramen and still have enough bone to be removed to make a visible external shortening effect. This is really a ‘reverse hinge’ maneuver. The vertically reduced chin bone is put back together with two small titanium plates and screws or even resorbable sutures can be used. As the soft tissue attachments remain intact along the inferior order of the chin the soft tissue pad follows also creating somewhat of a soft tissue ‘reduction’ effect as well.
Horizontal Setback Bony Genioplasty
As the chin bone can be moved forward by an osteotomy, it can also be moved back. While this type of setback bony genioplasty can be done for a protruding chin, as a general rule it is not a good operation for macrogenia. When the chin bone is moved more posteriorly several adverse aesthetic effects occur. The back edges of the downfractured chin ‘wings’ get pushed below the inferior border creating a raised edge of palpable bone along the inferior border. This also causes a soft tissue submental bulge or fullness as the soft tissues that surround the chin get pushed backward and downward. While a forward movement of the chin bone stretches out and favorably expands the chin and submental tissues, a backward movement compresses them and unfavorably bunches them together.
However, there is a role for setting back the chin known as a reverse bony genioplasty. This is done in cases where the chin has been brought too far forward by a prior bony genioplasty and is causing an aesthetic issue or the patient has persistent chin tightness and discomfort. Using the same osteotomy line, the bone cut is remade and the chin moves back either partially or completely based on patient desires. (Fig. 17) The bone will heal just as well as it did from the first osteotomy. This revision procedure is easier to do when plate fixation has been previously used as opposed to lag screw fixation. The adverse soft tissue effects do not occur in this type of subtotal reversal of a primary advancing bony genioplasty.
Dr. Barry Eppley