Genioplasty — The chin moves in three dimensions, not one
Classification of chin deformities in three planes, the trap of using genioplasty for what is a mandibular position problem, the basal osteotomy step by step with all its movements, hemigenioplasty for asymmetry and the bone versus implant debate.
Content intended for healthcare professionals. It does not replace clinical assessment and is not written as patient information.
Key points
- The chin is analysed in three planes at once — sagittal, vertical and transverse — and in each there may be excess or deficiency. Thinking of it only as "underprojected" is what produces advanced, overlong chins.
- Before operating on the chin, rule out that the problem is the position of the whole mandible. A genioplasty over a retrognathia disguises the profile but corrects neither the occlusion nor the airway.
- The basal osteotomy is one technique with many movements: it advances, sets back, shortens, lengthens, centres and rotates. That versatility is what separates it from an implant, which does only one thing.
- Chin asymmetry is not corrected by moving the whole segment: hemigenioplasty treats one side without displacing the other.
- What ruins a well-executed genioplasty is almost never the bone: it is failure to reinsert the mentalis muscle, and the result is chin ptosis, which is hard to correct afterwards.
Analysing the chin in three planes
The usefulness of a classification lies not in naming things but in forcing you to look at what you would not have looked at. In the chin, that was precisely the contribution of practical classifications: separating the problem into independent planes. In the sagittal plane the chin may be retruded or protruded, and that is all most people examine. In the vertical plane it may be excessively long or short, and this dimension is the most overlooked: a long chin with normal projection reads as a long face, not as a chin problem. In the transverse plane it may be deviated to one side or asymmetrical in shape without being deviated. And combinations exist: the commonest in practice is the retruded and vertically excessive chin, which if treated by advancement alone ends up worse than before because it accentuates the length. The practical consequence is simple: the surgical plan is written as three numbers, not one.
The deformities and their correction
| Deformity | How it looks | Movement of the segment |
|---|---|---|
| Sagittal microgenia | A profile with the chin behind the reference line and an effaced labiomental fold, the lower lip appearing prominent | Pure advancement of the basal segment. It is the most rewarding movement and the best tolerated by soft tissue |
| Sagittal macrogenia | A chin projecting beyond the profile with a deep labiomental fold | Setback of the segment, or wedge resection. Setback leaves excess soft tissue that must be managed at closure |
| Vertical excess | A lengthened lower third, often with lip incompetence and mentalis strain to close the mouth | Resection of a horizontal strip of bone between two parallel osteotomies, with or without simultaneous advancement |
| Vertical deficiency | A short lower third, with the chin flattened against the neck | Lowering the segment with an interpositional graft in the gap, or distraction if the defect is large. It is the least stable movement |
| Transverse asymmetry | The chin point deviated from the facial midline, often accompanying a larger mandibular asymmetry | Centring by lateral sliding of the segment, or hemigenioplasty if the problem is volume on one side rather than position |
| Combined: retruded and long | The commonest presentation in clinic, and the one that fares worst if treated in a single plane | Advancement plus strip resection in the same operation: projection is gained while the lower third is shortened |
The prior question: is it the chin or the mandible?
This is the fork that decides everything else, and it is resolved by looking at the occlusion, not the profile. If the patient has a Class I with sound occlusion and the chin falls short, the problem is the chin and genioplasty solves it. If they have a Class II with increased overjet, what is retruded is the whole mandible, and there genioplasty disguises the profile without correcting anything that matters: the occlusion is unchanged, the posterior airway space is unchanged and the joint still works in the same position. In patients with obstructive sleep apnoea that difference stops being aesthetic. It is worth saying plainly in clinic, because genioplasty is cheaper, shorter and involves no orthodontics, and is therefore tempting for both parties. The reasonable working rule: the chin is operated on alone only when the rest of the skeleton is in place; if it is not, genioplasty is the last step of orthognathic surgery, not a substitute for it.
The basal osteotomy, step by step
- IncisionVestibular, leaving at least 1 cm of mucosa attached to the lip so it can be closed and, above all, so there is somewhere to reinsert the mentalis. Incise obliquely towards the bone to preserve a muscular cuff
- ExposureSubperiosteal until both mental foramina are identified, the safety landmark. Laterally, undermine only what is needed: the periosteum of the mandibular bases maintains the segment’s blood supply
- MarkingA vertical midline reference marked with a burr before cutting: once the segment is mobilised there is no way to know how far it has moved or whether it is centred
- OsteotomyHorizontal, at least 5-6 mm below the mental foramen and the dental apices, extended far enough posteriorly for the step to be camouflaged. Fine saw or piezoelectric device
- Movement and fixationThe segment is moved to the planned position and fixed with a preformed plate or screw osteosynthesis. Before fixing, check the midline and the symmetry of the lateral steps, where unintended rotation shows
- The stepsBurr the lateral edges of the displaced segment until the transition is continuous. An 8 mm advancement leaves two palpable steps if they are not smoothed, and the patient notices them before the improvement
- The closure, which is the keyReinsert the mentalis muscle to the periosteum of the segment with resorbable sutures, and only then close the mucosa. This step is not optional: it separates a good result from chin ptosis
Hemigenioplasty for asymmetry
When the chin is asymmetrical, the instinctive reaction is to shift the whole segment towards the short side, and that often makes things worse: the chin point is centred but a step is created on the side that was fine. The alternative described for these cases is hemigenioplasty, treating only one side of the chin: an osteotomy that does not cross the midline, with displacement or interposition limited to the deficient hemichin. Its natural indication is unilateral asymmetry of volume or height with the chin point in acceptable position, the situation in which moving the whole thing solves nothing. Like all asymmetric surgery, it demands more careful planning than symmetric work: references must be taken from the sound side and transferred, and intraoperative checking is done with measurements rather than by eye, because the baseline asymmetry distorts the surgeon’s perception just as it does the patient’s.
Bone versus implant
| __Basal osteotomy__ | __Alloplastic implant__ | |
|---|---|---|
| What it can correct | All three planes and their combinations: projection, height, width, asymmetry and rotation | Essentially sagittal projection and some width depending on the design. It does not correct vertical excess |
| Stability | Bony union. The result is definitive once consolidated | It depends on fixation and on the pocket. The specific complication is resorption of the underlying bone beneath the implant |
| Reversibility | None in practice: redoing a genioplasty is a major reoperation | It can be removed, and that is its real advantage. Also its risk: infection and extrusion force removal |
| Complexity and time | Greater: osteotomy, osteosynthesis and a real learning curve | Less, and that is its appeal. The error is letting simplicity decide the indication |
| When it makes sense | By default, and obligatorily when there is a vertical component or asymmetry | Pure, moderate sagittal deficiency, in a patient who refuses the bony approach or has a contraindication to it |
What can go wrong
- Mental nerve sensory disturbance. Transient lower lip hypoaesthesia is common and usually recovers; permanent loss is rare if the osteotomy respects the safety margin. The commonest cause is not the cut but retractor traction on the nerve during exposure.
- Chin ptosis, with soft tissue drooping over the bony edge and a bagged appearance. It is the direct consequence of an unrepaired mentalis detachment, and is prevented at closure because correcting it later is far harder.
- Palpable steps and contour asymmetry, almost always from not burring the lateral edges or from unnoticed rotation of the segment at fixation.
- Injury to the incisor and canine apices if the osteotomy is too high. The margin is measured on the panoramic radiograph or CT beforehand, not estimated.
- With an implant the list differs: displacement from an oversized pocket, infection, extrusion and resorption of the underlying bone, which can cancel out the effect achieved.
Soft tissue does not follow bone millimetre for millimetre
This is why purely skeletal planning fails at the postoperative visit. The soft-tissue response to chin movement is not one-to-one and is not the same for all movements: advancement transmits reasonably well to the profile, but setback leaves an excess of tissue that does not retract in the same proportion and can end in a submental contour worse than the starting one. Soft-tissue thickness over the symphysis further modulates the effect, analogously to skin in the nose: over a thick-tissue chin, more bony movement is needed to see the same change. The practical conclusion is that the figure in the surgical plan and the figure on the profile are not the same, and that when setting back, it is worth planning simultaneously what to do with the redundant soft tissue rather than leaving it to see how it settles.
Deciding the manoeuvre
Is the occlusion sound?
In how many planes is the chin altered?
References
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Related specialty: Chin Surgery