deformity? A witch’s chin deformity is present when there is soft-tissue ptosis of the chin caudal to the menton that results in an exaggerated submental crease. During an intraoral approach to genioplasty, the mentalis muscle is transected. To prevent subsequent ptosis, the mentalis should be reattached to the mandible and repaired during closure. The remaining muscles are relevant to local anatomy of the chin and lower lip but are neither specifically relevant to the witch’s chin deformity nor genioplasty.1,2 Alternative methods to avoid a witch’s chin deformity following osseous genioplasty include minimizing soft-tissue dissection or degloving in the first instance.3 The depressor anguli oris and depressor labii inferioris are paired muscles of facial animation that pull the lower lip downward due to their attachments from the mandible to the orbicularis oris and lower lip dermis. The geniohyoid muscles are paired narrow muscles that pass from the hyoid to the mandible. They have a role in swallowing by elevating the tongue and hyoid. The genioglossus muscles are paired extrinsic muscles of the tongue. They form most of the tongue mass and serve to protrude and deviate the tongue.
2. Guyuron B, Michelow BJ, Willis L. Practical classification of chin deformities. Aesthetic Plast Surg 1995;19(3):257–264
3. Lambi AG, Byrd R, Bradley C, Volpicelli E, Bradley JP. Abstract QS05: Osseous genioplasty: prevention of witch’s chin deformity with custom-milled plates. Plast Reconstr Surg Glob Open 2018;6(4 Suppl):116–117 IATROGENIC NERVE INJURY DURING GENIOPLASTY 2. Which nerve is most at risk of inadvertent injury during a sliding genioplasty? The mental nerve is at risk of damage during a sliding genioplasty if the osteotomy is placed too high or if the mental foramen is lower than anticipated. The mental nerve supplies sensation to the lower lip and dentition and is a continuation of the inferior alveolar nerve which passes through the mandible. There have been a number of anatomical and clinical studies undertaken to assess the location of the mental foramen and mental nerve, particularly relevant in the micrognathic mandible in order to reduce risk of this complication.1–3 The inferior alveolar nerve is a branch of the mandibular division of the trigeminal nerve. These two nerves are too proximal to be at significant risk during genioplasty. The hypoglossal nerve supplies motor function to the tongue but is well protected during a genioplasty. The marginal mandibular nerve is also protected during a genioplasty, as it lies above the lower border of the mandible and lateral to the area of dissection.
plane? When assessing the profile of a patient before genioplasty, the relationship between the upper and lower lips and pogonion needs to be considered. Ideally, the upper lip should be just anterior to the lower lip, and the lower lip just anterior to the soft-tissue pogonion.1 Riedel’s plane is a straight line that connects the most prominent parts of the upper and lower lip in lateral view, which on a balanced face should also touch with the soft-tissue pogonion (the soft-tissue pogonion is the most projected soft-tissue point covering the mandible; Fig. 117.2). (Note there is slight variation between males and females in ideal chin prominence, with the male chin having greater prominence). Chin advancement beyond the lower lip will result in an artificial appearance with poor aesthetics; so, it must be avoided.1
Soft-tissue movement during genioplasty follows bony advancement predictably, with a ratio close to 1:1 (the precise amount varies slightly between 0.8:1 and 1:1). However, this ratio does not hold true for posterior repositioning of the chin, which may be reduced. For this reason, outcomes are less predictable for prominent chin correction, and the potential soft-tissue effects must be taken into account during preoperative planning. Osseous genioplasty provides good flexibility for the correction of chin deformities in multiple planes, and this represents an advantage over prosthetic techniques.1 Most commonly, it is used for horizontal (sagittal) advancement but can also be used to increase or decrease vertical deformities and amend symphyseal asymmetries. A jumping genioplasty is indicated for very minor vertical excess correction, where there is horizontal deficiency. Larger excesses are better treated by reduction genioplasty. A jumping genioplasty involves movement of the inferior-most part of the mandible anteriorly and superiorly as an onlay to augment a horizontal deficiency. The labiomental crease should normally be about 4 mm deep in women and 6 mm deep in men. Deep (not shallow) labiomental folds will be exacerbated by horizontal chin advancement or by shortening the vertical chin height. Therefore, when advancing the chin in patients with a normal or short lower face height, vertical advancement of the chin can be incorporated into the sliding genioplasty to compensate and thus maintain a normal labiomental fold depth. This approach must not be used in patients with long lower faces, and these patients are better served with orthognathic procedures.1–3
In general, alloplastic augmentation of the chin should only be used for patients with a mild horizontal chin deficiency in the sagittal plane and with a shallow labiomental fold. It may be preferred by cosmetic surgery patients and can be incorporated into face and neck lift procedures where a submental incision is already planned. Implant types include silicone and porous polyethylene. These can be “off the shelf” or customized to each individual patient. The latter are typically custom 3D printed. Alloplastic chin augmentation cannot correct excess horizontal deficiency, vertical deficiency of any severity, mandibular asymmetry, significant microgenia, or malocclusion. Contraindications to implant use include the presence of infection, poor dentition with active dental disease, diabetes, immunocompromise, and smoking.1–4
Implant genioplasty may be performed via intraoral or extraoral approaches. The advantage of an intraoral approach is that external scars are completely avoided. The alternative to the intraoral approach is a submental approach, which involves a short, transverse skin incision placed just behind the submental crease. This hides the scar discretely and provides access, which can also be useful when combined procedures such as a neck lift or corset platysmaplasty are required. Further potential benefits of using the submental approach are a more precise implant placement, reduced risk of mental nerve damage and avoidance of the creation of a witch’s chin deformity. The two approaches have similar rates of infection, which may be counterintuitive as one may expect infection rates to be higher when inserting a prosthesis through the oral cavity, because of the high number of pathogens within the mouth. However, this element does not need to be a major factor to consider when selecting the preferred approach. Operative times are comparable with either approach and are more likely to be affected by surgeon and patient factors rather than the approach itself.1–3
The most common complication of those listed following genioplasty is a transient lower lip paresthesia which is seen almost universally. This resolves in almost all patients who have solely undergone genioplasty without other combined procedures such as orthognathic surgery, where rates of continued paresthesia are between 15 and 29%.1,2 Hematomas are rare and most often occur at the osteotomy site in association with an osseous genioplasty. Infection is less than 5% for implant genioplasty and 3% for osseous genioplasty. Extrusion of implant or metalwork is also rare. Lower lip weakness can occur leading to drooling, but again is usually temporary and not common. The most common complication following genioplasty is a poor aesthetic outcome, but in spite of this, patient satisfaction rates are very high (>90%). Poor aesthetic outcomes include overcorrection, undercorrection, and asymmetry.1,3