Continuing Education Activity

The chin represents an often underappreciated aesthetic component of the face; however, the chin remains an essential facial subunit that plays a significant role overall facial attractiveness. Chin augmentation, or genioplasty, is a common facial plastic surgery procedure used to improve facial aesthetics. To fully appreciate the effects that chin augmentation can provide for the patient, the surgeon must perform a complete facial evaluation and possess a thorough understanding of the relevant anatomy. Although several methods exist to augment the chin, including osseous genioplasty, this activity will focus specifically on chin augmentation using alloplastic chin implants. This activity also describes the process of patient assessment, critical facial analysis, and the techniques involved with alloplastic chin augmentation and highlights the role of the interprofessional team in patients who undergo this procedure.

Objectives:

• Describe the different methods for chin and facial analysis when considering chin augmentation using alloplastic implants.
• Identify the most common indications for chin augmentation using alloplastic implants.
• Summarize the techniques of inserting chin implants.
• Review the risks associated with chin augmentation using alloplastic implants.

Introduction

The chin represents an often underappreciated aesthetic component of the face; however, the chin remains an essential facial subunit that plays a significant role in overall facial attractiveness. Chin augmentation, or genioplasty, is a common facial plastic surgery procedure used to improve facial aesthetics. To fully appreciate the effects that chin augmentation can provide for the patient, the surgeon must perform a complete facial evaluation and possess a thorough understanding of the relevant anatomy. Although several methods exist to augment the chin, including osseous genioplasty, this article will focus specifically on chin augmentation using alloplastic chin implants.[1]

Anatomy and Physiology

Structures Encountered During Alloplastic Chin Implantation[2]

• Skin and subcutaneous tissue
• Mentalis muscle
• Mandibular periosteum
• Gingivolabial mucosa (if the intraoral approach is used)
• Mental nerve

Anatomic Structures at Risk

• The mental nerve is a branch of the inferior alveolar nerve from trigeminal nerve mandibular division which exits the mandible in the vicinity inferior to the first premolar. NOTE: Damage can be avoided by maintaining a dissection plane on the inferior-most aspect of the mandible. If an intraoral approach is used the nerves can be directly visualized and preserved; this may facilitate precise placement of more rigid implants such as Medpor, and may or may not be required in smaller or more flexible chin implants.
• The mentalis muscle will cause a ptotic chin if not re-approximated properly.

Indications

A chin implant is often reserved for those patients looking to correct their convex facial profile and/or narrow chin usually caused by:[2][3]

• Horizontal (anterior-posterior) chin deficiency, also known as microgenia
• Soft tissue deficiency (e.g., muscular atrophy)
• Pre-jowl volume loss 

Chin implantation is most often employed in conjunction with rhinoplasty to create a harmonious nose-chin relationship and aesthetically pleasing profile, and may be indicated in up to 25% of patients presenting for cosmetic rhinoplasty. Chin augmentation can significantly improve the results of a facelift by lengthening the jawline and providing a better framework over which to reposition the soft tissues of the face.

Contraindications

Contraindications to chin augmentation using alloplastic implants include:[2][3]

• Suboptimal vertical chin height (i.e., shortened mandibular height)
• Retrognathia associated with dental malocclusion
• History of previous rejection to the implanted material

A relative contraindication may include:

• Transverse chin asymmetry (may be addressed with a carefully shaped and customized implant)
• Deep mentolabial crease, as chin augmentation may accentuate this sulcus

Equipment

The ideal alloplastic implant for augmentation should have the following characteristics:[1]

• Easily shaped and secured
• Biologically inert
• Noncarcinogenic
• Noninflammatory
• Nonallergenic
• Easily available
• Maintain its desired form and consistency in situ
• Resistant to mechanical strain
• Integrate into the surrounding tissue

The most common alloplastic implant materials used for chin augmentation consist of:

• Silastic (solid silicone) - nonallergenic, minimally reactive, nonporous (i.e., does not allow for fibrovascular ingrowth) and easily manipulated; causes a local inflammatory response resulting in the formation of a surrounding fibrous capsule; exist in a variety of shapes, sizes (small, medium, large), and styles (narrow button style, extended with tapering lateral wings) and come with sizers as well to help gauge the three-dimensional contouring change that will occur.
• High-density porous polyethylene - nonallergenic and nonabsorbable implant with large pores (150 micrometers) which allows fibrovascular ingrowth of surrounding tissues; difficult to contour; difficult to remove
• Meshed materials such as polyamide - flexible material that can be easily shaped and manipulated; elicits a moderate foreign body reaction; allows ingrowth of fibrous tissue
• NOTE: Expanded polytetrafluoroethylene (ePTFE), a once commonly used biomaterial, is now off the legal market in most locales

Preoperatively

• Standard photography capturing straight, oblique, and lateral/profile views
• Preoperative antibiotics (e.g., weight-based cefazolin)
• Alcohol solution or pad (cleanse skin before injection and marking landmarks and proposed incisions)
• Surgical marker (marking planned incision sites)
• Local anesthesia (such as lidocaine 1% with epinephrine 1 to 100,000; maximal dosage of lidocaine with epinephrine is 7 mg/kg)
• Topical antiseptic, such as povidone-iodine

Intraoperatively  

• Variety of curved dissectors and periosteal elevators
• Scalpel (e.g., #15 blade)
• Forceps (with teeth for atraumatic soft tissue handling)
• Electrocoagulation/electrocautery device
• Skin hooks and/or small retractors
• Suture (e.g., 4-0 absorbable for deep layers, and 5-0 nonabsorbable for skin) 
• Antibiotic-impregnated solution for soaking the implant and irrigating the wound

Postoperatively

• Antibiotic ointment
• Chin dressing materials (non-stick dressing, adhesive tapes)

Personnel

Depending on a number of factors (patient's pain threshold, patient anxiety, patient overall health, the complexity of the procedure, surgeon comfortability and skill level, etc.) a chin augmentation with an alloplastic implant may be done either under local anesthesia (with or without oral anxiolysis and analgesia) or via deeper sedation or general anesthesia.

Personnel needed for the procedure performed under local anesthesia:

• Nurse assistant

Personnel needed for the procedure performed under deep sedation or general anesthesia:

• Anesthesiologist 
• Operating room nurse
• Scrub technician or nurse
• Surgical assistant 

Preparation

A comprehensive evaluation of the chin should be performed in three dimensions with the vertical (superior-inferior), horizontal (anterior-posterior), and transverse dimensions recognized. In addition, the chin position relative to the lips, teeth, maxilla, nose, and soft tissues of the neck should be taken into account. Often, photographic analysis is sufficient for minor deformities that will require an alloplastic implant; however, if the deformity is more significant (e.g., vertical height excess or transverse asymmetry), a radiograph is often warranted.

Several techniques exist to help evaluate those patients who may benefit from a chin augmentation:

• Goode described a line perpendicular to the Frankfort horizontal line that passes through the alar groove. In this method, he determined that the pogonion (most prominent or anterior point of chin projection) must be in the same plane as this line or immediately posterior to it.[4]
• Gonzalez-Ulloa proposed a line that also runs perpendicular to the Frankfort horizontal line and passes through the nasion (the deepest portion of radix). In this case, the pogonion should reach that line or be immediately posterior. He further classified the degree of insufficiency as grade I being within 1 cm posterior to this line, grade II between 1 to 2 cm posterior, and grade III as greater than 2 cm posterior.[5]
• Silver suggested a line that passed perpendicular to the Frankfort horizontal line passing through the mucocutaneous junction of the lower lip. He determined the pogonion should project to this line or, more ideally, for women be within 2 mm posterior.[6]
• Merrifield took a similar but somewhat different approach for chin analysis in describing the Z-angle, which is formed by the Frankfort horizontal line and a line passing through the pogonion and the most anterior projection point of the lips. Ideally, this angle should be between 75 and 85 degrees.[7]
• Legan also proposed an angle-based chin analysis formed from a line traversing the glabella and subnasal point and a line traversing the subnasal point to the pogonion with an ideal value of 12 degrees (range of 8 to 16 degrees).[8]

Lastly, two well-described facial angles required for complete chin analyses are: the cervicomental angle (CMA) and the mentocervical angle (MCA).

• The CMA is formed by a tangential line from the submental point and a line tangential to the neck at the subcervical intersection or the lowest point between the submental area and the neck. Ideally, the CMA will be 121 degrees for men and 126 degrees for women.
• The MCA is most commonly described as an angle formed between a line passing through the nasal tip and pogonion and a tangential line that passes through the submental point with an ideal angle ranging from 110 to 120 degrees.[9]

While all of these methods offer insight as to an ideal chin position relative to the lips, face, and even neck, only a limited number take into account the relationship between the nose and chin. This is an important relationship not to overlook as they directly correlate to each other’s relative appearance in space, with the general rule being that the more projected the nose, the less projected the chin appears to be and vice versa. There is an essential, and ideal, harmonious balance between projection of the chin and nose. Furthermore, it is important to recognize that all of the analysis methods mentioned are based on standardized photography methods, four of which rely on the Frankfort horizontal line, which is a well-known anatomic horizon extending from the superior border of the external auditory canal to the inferior orbital rim.[5] Furthermore, radiographic evaluation in the form of a panoramic radiograph and/or lateral and AP radiographs may be useful for more complex deformities such as vertical height excess, orthognathic deformities, and transverse asymmetry as seen in hemifacial microsomia, oculoauricular vertebral (OAV) syndrome, or even as an isolated component of the anatomy.

Technique or Treatment

Once the patient is deemed a candidate for an alloplastic implant, and the type and size of the implant are selected, the decision must be made whether to perform the procedure via an intraoral or submental approach. In short, the transoral approach has the benefit of no external scarring; however, the procedure is technically more difficult and is associated with increased risk of infection given the communication with the oral cavity. The submental approach, on the other hand, may be preferred for several reasons: it offers better exposure for placement, as well as access to the neck for any additional procedures to be performed (e.g., concomitant facelift, neck lift, platysmaplasty, liposuction). It also avoids potential contamination of the implant by oral secretions.[1][10][11]

Submental Transcutaneous Approach

• An approximately 2 cm midline incision is placed just posterior to the existing submental crease. NOTE: Do not place the incision in the submental crease because chin augmentation will cause anterior skin movement, and thus a scar positioned anterior to the native crease.
• Sharp dissection is then performed (with a scalpel or electrosurgical knife) through the skin and underlying soft tissues, through the mentalis muscle, and down to the mandibular periosteum.
• Two vertical incisions are made in the periosteum 1 to 2 cm lateral to the midline in order in preparation for the subperiosteal dissection. NOTE: Leaving the center portion of the implant in a supra-periosteal plane may decrease bony mentum resorption and create a more defined subperiosteal tunnel bilaterally. 
• Subperiosteal dissection using a periosteal elevator such as a Freer, Joseph, or #9, is then carried out laterally along the inferior border of the mandible (no more than 10% the size of the implant) for the length of the implant wings (approximately 5 cm in most implants) with care taken not to extend the pocket more than 1 cm superiorly. This maintains a tight pocket and avoids damage to the mental nerve, as well as minimizing the risk of implant migration to an undesired, superior position. 
• The implant is then inset first on one side and then folded on itself, allowing the other side limb to be placed. NOTE: Minimal manipulation of the implant should occur once removed from its sterile packaging to mitigate the risk of infection or fracture/damage to the implant itself. In addition, the implant can be dipped or soaked in an antibiotic solution while awaiting implantation.
• The implant is secured by suture to the periosteum in the midline inferiorly.
• The mentalis muscle is reapproximated.
• The wound is closed in layers using absorbable sutures for the subcutaneous tissue and deep dermis, and non-absorbable everting sutures to approximate the skin. 
• A splint-like dressing is applied using an antibiotic ointment, non-adhesive gauze, and adhesive tape 

Intraoral Approach

• If performing an intraoral approach, a 2 to 3 cm gingivolabial incision can be made with similar subsequent dissection through the mentalis muscle down to the periosteum with the placement of the implant in a supra-periosteal plane centrally and the lateral wings placed sub-periosteally. Once again, maintaining a dissection plane along the inferior aspect of the mandible will decrease the risk of mental nerve injury. The wound is copiously irrigated with antibiotic solution, and the wound closed in layers (using absorbable suture) with care to approximate the mentalis and to create a water-tight seal.

NOTE: While not part of this discussion, it would be prudent for those who routinely encounter patients with microgenia or retrognathia and who perform chin augmentation to have a sound understanding of the anatomy and principles relevant to sliding genioplasty as well.[12]

Complications

Generally speaking, chin augmentation using alloplastic implants (whether placed via a transoral or subcutaneous approach)  represents a relatively straightforward procedure with a low-risk profile and a high (97.8%) satisfaction rate.[13]

Nevertheless, complications arising from alloplastic chin implantation certainly exist and include:[14][15]

• Hematoma
• Infection - less than 1%
• Paresthesia/dysesthesia - generally transient in nature but can be prolonged (months)
• Implant malposition - 2.5%
• Implant migration (i.e., secondary displacement) - 5.0%
• Implant extrusion - 0.4%
• Implant-induced resorption of the mentum - 8.3%
• Implant rejection
• Alopecia of the submental incision

Tips to avoid complications have been elucidated above, but include:[1] 

• Maintaining a small supraperiosteal strip centrally (limits bony resorption)
• Dissecting a narrow subperiosteal plane laterally to accommodate the chosen implant (limits implant migration) snugly
• Staying along the inferior border of the mandible (lessens mental nerve injury and promoted an aesthetically positioned implant)
• Limiting the manipulation of the implant once removed from the sterile packaging (lowers infection risk)
• Using an antibiotic solution to bathe the implant and irrigate the recipient compartment (lowers infection risk)
• Creating a multilayered and watertight wound closure (prevents extrusion and infection).
• Using the transcutaneous approach versus the transoral approach (theoretically lessens infection risk, though the literature remains inconclusive)
• Using a transoral approach in men (avoids submental scar and associated alopecia)

NOTE: While not routinely used, some authors advocate using screw fixation to prevent the migration (secondary displacement) of an implant.[16] 

Clinical Significance

An alloplastic chin implant is used to augment chin projection and can be used to provide a more attractive appearance of the face. Increasing the projection and/or width of the chin to provide a more balanced nose-chin relationship or more pleasing pre-jowl area, respectively, are two examples where this is especially apparent. When performing an alloplastic chin implantation, a comprehensive understanding of the anatomy and precise surgical technique are essential to achieving optimal results.

Enhancing Healthcare Team Outcomes

Before performing an alloplastic chin augmentation procedure, it is important to perform a thorough preoperative assessment and identify any potential risk factors specific to the patient. A team approach is always ideal to ensure the procedure is performed to the highest possible standards. Prior to surgery, the patient should have the following done:

• Evaluation by a surgeon experienced in selecting the appropriate patient for the surgery.
• Evaluation by primary care physician, anesthesiologist, and nurse anesthetist to ensure that the patient is fit for general anesthesia (if applicable).
• Evaluation and monitoring by the preoperative and postoperative specialty nurses to assist with coordination of care and patient education.

An interprofessional team consisting of personnel experienced in chin implantation (e.g., surgeon, anesthesiologist, surgical assistants, operative nurses, etc.) should perform the alloplastic chin implantation for the best outcomes. If performed in the clinic, a nurse fully dedicated to monitoring the patient (particularly if using sedation) is strongly recommended. A close follow-up should be scheduled in the post-operative period to ensure there are no signs of infection, hematoma, or rejection that occur. The patient should also be educated on avoiding strenuous activity, heavy lifting, or stooping over within the first week post-operatively to prevent complications. By following these basic steps, outcomes should be favorable when performing alloplastic chin implantation. [Level 5]

Nursing, Allied Health, and Interprofessional Team Interventions

Recovery time can be reasonably expected to take 3 to 5 days for most individuals, though swelling and bruising may persist for up to 2 weeks, depending on the extent of surgery (size of implant), among other individual patient factors. Pain is typically mild to moderate; however, over-the-counter analgesics (e.g., acetaminophen 1000 mg every 8 hours as needed for pain) may be supplemented with prescription-strength medication per physician and patient preference. Post-operative antibiotics (with oral flora coverage) may be given for 5 to 7 days and is strongly encouraged if a transoral approach was used. The patient is instructed to eat a soft diet (avoiding biting with the front teeth), keep the head elevated, routinely apply ice to the area, employ good oral hygiene (e.g., salt water rinses before and after meals), and avoid strenuous activity for two weeks — patients follow-up in roughly seven days for wound assessment and suture removal. Photographic documentation may take place at the 3-month visit.

Nursing, Allied Health, and Interprofessional Team Monitoring

Regardless of where the procedure is to be performed (clinic, hospital, surgery center), a recovery nurse fully dedicated to monitoring the patient is strongly recommended to detect serious complications such as hematoma formation. Close follow-up within 1 week should be scheduled in the clinic in the post-operative period to ensure there are no signs of infection, hematoma, or rejection.