Virtual surgical planning and computer-assisted design/computer-assisted manufacturing in facial feminization surgery

Introduction

Background

Facial feminization surgery (FFS) is an essential component of the multidisciplinary treatment of gender dysphoria. First described by Ousterhout in the 1980s, FFS has become increasingly common following recent approval of Medicare reimbursement for gender confirming surgery. ^, Precision and careful preoperative planning are paramount in FFS due to transformation of normal preoperative masculine anatomy into a feminine appearance rather than restoration of normal from abnormal form in congenital or traumatic craniofacial conditions.

A range of preoperative planning techniques and intraoperative “guides” have been used to determine the location of osteotomies for FFS osseus manuevers. These include transillumination of the frontal sinus on perioperative clinical exam, preoperative assessment of sinus dimensions on radiograph or computed tomography (CT) scan, ^, as well as measurements of various anthropometric landmarks. Intraoperative assessment alone based on surgeon experience without preoperative imaging, ^, three-dimensional (3D) printing of patient skulls to simulate maneuvers prior to surgery, ^, and 3D photogrammetry have also been described. However, once planned by the aforementioned methods, osseus maneuvers-such as frontal setback, reduction genioplasty, and gonial angle reduction-were traditionally performed entirely freehand. The advent of computer-assisted design/computer-assisted manufacturing (CAD/CAM) and its widespread application in pediatric craniofacial and orthognathic surgery marked the transition to guide-directed osteotomies, ^, which were then adopted in the growing field of gender confirming facial surgery.

Indications

Facial gender affirmation surgery is an essential component in the treatment of gender dysphoria. Similar to all other aspects of gender transition, the need and the anatomical areas treated in facial surgery are highly individualized and dependent upon the triggers for dysphoria in each patient. Although WPATH Standards of Care V7 does not outline specific criteria for FFS, our typical preoperative protocol for proceeding with facial feminization surgery include the following for all patients:

Evaluation by a multidisciplinary group of gender health specialists
Two letters of support from gender health specialists with at least one from a licensed mental health provider
Robust patient support network
12-month trial in the gender-identity congruent role ± medical transition
Agreement from the senior surgeon that the patient is medically, socially, and psychologically ready for surgery
Patient must be at skeletal maturity

Indications for CAD/CAM in FFS have been subject to debate. ^, ^, Certain authors advocate against the use of CAD/CAM under the pretense that a “color by number” approach risks a standardized process lacking consideration of individualized anatomy and aesthetic. ^, Critics also comment that CAD/CAM relegates the surgeon to a technician that “cuts along the dotted lines” and inhibits learning. ^, However, multiple authors report using computer-assisted planning of some kind for FFS. ^, ^, Deschamps-Braly et al. routinely obtain 3D CT face and panorex imaging prior to reduction genioplasty, but utilize CAD/CAM for challenging cases to achieve the most feminine results. Interestingly, Capitán et al. even reported designing specific FFS-related CAD/CAM software.

In our practice, we perform CAD/CAM for all patients prior to FFS for intraoperative precision, safety, and speed of all skeletal moves. Decision-making during the CAD session is based on clinical exam, cephalometric measurements, and are secondarily double-checked using a reference female skull. Because FFS is a combination of hard tissue and soft tissue maneuvers, one note of caution is that precision planning and execution of the bony maneuvers is not the only factor necessary to achieve optimal results.

Contraindications

Patient factors:

Unrealistic expectations
Inappropriate motivation for gender affirming surgery
- Ulterior motives or possible comorbid psychiatric conditions, such as body dysmorphia

Surgical contraindications:

Medical comorbidities that preclude prolonged surgery/general anesthesia
Skeletal immaturity
- Skeletally immature bone lacks the rigidity required for the precise osseus maneuvers
- Delaying surgery until skeletal maturity reduces disruption of normal facial skeletal growth and maximizes postoperative symmetry
Older age, independent of surgical candidacy, is not a contraindication

Contraindications to CAD/CAM:

No specific contraindications
Cost of CAD/CAM and custom guide manufacturing can be significant, and may not be available depending on the practice setting and institution

Clinical considerations

Naturally, the key anatomical considerations in FFS center around the differences between the male and female facial skeleton and soft tissues. ^, In regard to underlying skeletal framework, masculine faces tend to have more prominent and angular features, while females tend to have obtuse, softer features. Table 23.1 provides a review of the key anatomical differences of the underlying facial skeleton and overlying soft tissues in male and female patients, as well as the relevant maneuvers to address these differences in FFS.

Table 23.1

Differences in male/female facial characteristics and their management in facial feminization surgery

Characteristic	Male	Female	Procedure
Frontal bone	Larger, broader frontal bone Larger frontal sinus Flat and retroclined frontal bone on lateral view	Smaller frontal bone Smaller frontal sinus Gentle curve from frontonasal junction to hairline on lateral view	Anterior table setback Brow recontouring
Orbits	Prominent supraorbital bossing/lateral orbital hooding	No supraorbital bossing/lateral orbital hooding	Supraorbital recontouring Lateral orbital recontouring/ostectomy
Zygoma	Flatter, lower and less prominent zygomatic arch	Higher and more projecting zygomas	Zygomatic implants Fat grafting
Mandible	Wider lower facial width Acute gonial angle	Narrower lower facial width Gentler, less defined gonial angle	Gonial angle reduction
Chin	Wider and “boxier” chin with increased height and projection	Narrow, pointed chin, generally shorter and less projected	Chin recontouring Reduction genioplasty
Forehead hairline brow	Higher “M” shaped hairline with bitemporal recession Flatter brows that sit lower across the orbital ridge	Lower “O” shaped hairline without recession Curved brows that arch above the supraorbital rims	Hairline lowering Hair transplant Brow lift
Nose	Larger nose with acute glabellar and nasolabial angles Prominent dorsal hump or straight dorsum	Smaller nose with more obtuse nasolabial and glabellar angles Narrower with possible concavity or supratip break	Reduction rhinoplasty
Lips	Longer and thinner lips Minimal incisal show in repose	Fuller and shorter lips with increased visibility of the vermilion Greater incisal show in repose	Dermal lip augmentation Lip lift

As described by Ousterhout, forehead morphology can be further divided into four types based on radiographic findings and corresponding surgical treatment ( Table 23.2 ). Lateral orbital hooding, gonial angle/lower facial width, and chin width/height can also be stratified by severity; Hoang et al., for example, utilized a classification scheme of mild (1), moderate (2), and severe (3). However, management of these regions is less influenced by severity and requires consideration of other variables, such as the need for chin advancement rather than reduction alone, for appropriate operative planning.

Table 23.2

Ousterhout classification of forehead types

Forehead type	Defining features	Techniques for transformation
Type I	Mild bossing, no or minimum frontal sinus Thick anterior wall	Burring
Type II	Moderate bossing, midforehead flattening Normal forehead protrusion	Burring plus cement filling
Type III	Significant bossing, large projection Large frontal sinus with thin anterior table	Anterior frontal sinus wall setback
Type IV	Severe forehead slope not amenable to setback	Cement filling to create aesthetic forehead profile without setback

Key features of the clinical and radiographic examination of the patient considering facial feminization surgery are outlined in Fig. 23.1 and Table 23.1 .

Clinical examination

Systematic facial analysis
- Evaluation of the hairline
  - Hairline position
  - Hairline shape and temporal recession
- Evaluation of the forehead
  - Length at the midline and above the lateral brow
  - Eyebrow position/symmetry
- Frontal bone
  - Frontal view
    - Lateral orbital hooding
  - Lateral view
    - Supraorbital bossing
    - Contour
  - Mandible
  - Gonial angle
  - Gonial angle flaring
  - Lower facial width
  - Dental occlusion
- Chin
  - Length/height
  - Position/projection
- Lip length
- Upper white lip to red lip ratio
- Full nasal analysis

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