Authors: Huy-Young Kim, Sang-Baek Han
Categories: Cosmetic: Original Articles
Source: Plastic and Reconstructive Surgery
The authors’ main aim was to analyze soft-tissue response of the chin following genioplasty with anterior segmental osteotomy, which enables optimal surgical planning of genioplasty.
Sixty-two patients who underwent genioplasty with concomitant anterior segmental osteotomy were divided into three groups depending on the direction of pogonion (Pog) G1 (without sagittal change), G2 (advancement genioplasty), and G3 (setback genioplasty). All genioplasties included height reduction. Hard- and soft-tissue measurements with cephalometry were performed at T1 (before surgery), T2 (after surgery), and T3 (after orthodontic treatment) for the analysis of sagittal and vertical changes. Correlation and regression analyses were conducted to analyze soft- to hard -tissue movement and soft-tissue thickness changes.
During the T1 to T2 period, the horizontal soft- to hard-tissue ratio at Pog was 0.85 in G2 and 0.80 in G3, and the vertical ratio at menton (Me) was 0.9 for all groups. The correlation coefficients were 0.64 (G2) and 0.83 (G3) at Pog and 0.9 (all), 0.85 (G1), 0.95 (G3) at Me. There was no significant correlation between initial soft-tissue thickness and soft-tissue response ratio. During the T2 to T3 period, no significant relapses were observed, which demonstrates the stability of anterior segmental osteotomy combined genioplasty.
Clinically and statistically significant soft-tissue responses were demonstrated at Pog and Me. The higher values in G3 in particular suggest that setback genioplasty with anterior segmental osteotomy is an effective treatment alternative to conventional two-jaw surgery in some patients with bimaxillary prognathism with macrogenia.
Therapeutic, IV.
Genioplasty is an excellent adjunctive procedure that can be performed with other maxillofacial operations^1^ because of its predictability and stability.^1–11^ Postoperative results generally satisfy patients, with few complications.^2,12^
However, genioplasty alone is not sufficient to correct chins combined with bimaxillary protrusion. Anterior segmental osteotomy (ASO) is frequently performed in Asian patients with bimaxillary dentoalveolar protrusion.^13,14^ The advantages of this procedure are dramatic change, fast results, and minimal relapse, compared with orthodontic treatment.^14,15^
Soft- to hard-tissue ratios are essential for predicting soft-tissue response in genioplasty. According to a systematic review of soft- to hard-tissue ratios of the chin in orthognathic surgery,^16^ the horizontal ratio at pogonion (Pog) ranged from −0.27:1 to −0.70:1 (mean, 0.52:1) in setback genioplasty, and from 0.53:1 to 0.99:1 (mean, 0.85:1) in advancement genioplasty. The vertical ratio at menton (Me) ranged from −0.22:1 to −0.80:1 (mean, −0.43:1) in impaction genioplasty. Correlation coefficients between soft- and hard-tissue movement ranged widely (0.38 to 0.72). This high variability might be explained by the lack of correlation analyses or small sample sizes.^16^
Relapse should also be considered as a potential result. To our knowledge, no correlations between relapse and amount of osseous change in advancement genioplasty have been reported^7–9,12,16–19^ except in one study.^5^ Relapse after genioplasty is most likely attributable to postoperative remodeling.^1,19^
Previous studies of soft-tissue response following genioplasty focused mainly on advancement rather than setback genioplasty. Moreover, studies of the relationship between soft-tissue thickness and soft-tissue response, and vertical movement following genioplasty are rare.
In this study, we analyze horizontal and vertical soft-tissue response following genioplasty with ASO. Soft- to hard-tissue ratios, soft-tissue thickness changes, and relapse were studied to determine an optimal surgical plan for genioplasty. Our null hypothesis of this study was that soft tissue does not consistently follow hard tissue following genioplasty with ASO.
This study was reviewed and approved by the public institutional review board committee (P01-202202-01-023). The minimum meaningful number of patients was calculated by referring to the pioneer study of genioplasty by Bell et al.^20^ using power analysis by R (alpha = 0.05, power = 0.99), and was estimated to be a minimum of 24 (eight per group). Gpower 3.1.9.4 software was used to improve accuracy. Based on the sample size calculated using Gpower for comparing three groups with medium effect size of 0.4 (alpha = 0.05, power = 0.80, beta = 0.20), a total sample of a minimum of 45 (15 per group) was needed.
Sixty-two patients were selected from among 112 patients who underwent genioplasty concomitant with ASO at Seoul Cheil Plastic Surgery Clinic from March of 2017 to February of 2018 based on our inclusion and exclusion criteria. Genioplasties included vertical reduction with or without sagittal changes. All operations were performed by a single plastic surgeon (corresponding author). The average patient age was 31 years (range, 19 to 47 years). The sample included 19 men and 43 women. (See Table, Supplemental Digital Content 1, which shows demographic data of the patients, http://links.lww.com/PRS/G329.)
Inclusion criteria were (1) adults (age ≥19 years) who underwent vertical reduction genioplasty with ASO and postoperative orthodontic treatment and (2) patients for whom full follow-up cephalometry data were available for a period longer than 1 year. Meanwhile, patients who had (1) congenital malformation, (2) concomitant two-jaw surgery (Le Fort surgery of maxilla and sagittal split ramus osteotomy/intraoral vertical ramus osteotomy of mandible), (3) temporomandibular joint disorder, (4) history of orthodontic treatment, (5) possibility of vertical dimension change because of posterior teeth restoration, or (6) facial asymmetry greater than 5 mm were excluded.
Subjects were divided into three groups depending on the direction of Pog G1, without sagittal change; G2, with anterior displacement; and G3, with posterior displacement. T1 was the time before surgery, T2 was an average 2 months after surgery, and T3 was an average 1.6 years after orthodontic treatment. The numbers of patients in G1 [Pog_x (T2 to T1) between −1 and +1 mm], G2 [Pog_x (T2 to T1) > +1 mm], and G3 [Pog_x (T2 to T1) < −1 mm] were 18, 17, and 27, respectively.
The surgical treatment objective was produced by an orthodontist co-worker before surgery using mainly using two-dimensional cephalometry. The dental wafer was prepared through mock surgery.
Under nasotracheal anesthesia and povidone-iodine sterilization, four premolar teeth were extracted. Two small gingivovestibular incisions (left and right, 2.5 to 3.5 cm each) were created in the maxilla, and one prealveolar gingivovestibular incision was created in the mandible. Meticulous hemostasis and subperiosteal dissection were performed.
Precise ASO was performed following surgical pen markings. Anterior dentoalveolar bone segments of the maxilla and mandible, including six to eight teeth, were freed by vertical and horizontal osteotomy; they were moved back en bloc three-dimensionally according to the surgical plan. The dental wafer was used to obtain proper occlusion and planned posterior displacement.
Displaced bone segments were fixed rigidly using plates, screws, and interdental wiring. The wafer was removed and intermaxillary fixation was not applied.
Genioplasty was performed following ASO (Fig. 1). Periosteal dissection on the distal bone segment was cautiously restricted.
Fig. 1. Intraoperative view of genioplasty with ASO. 1, Mandibular ASO bone segment; 2, distal bone segment of genioplasty; 3, resected bone segment by two-step sandwich osteotomy; 4 and 5, Resected bone segments from the inferior border of the mandible for contouring bone stepping.
To reduce chin height, two horizontal or semihorizontal osteotomies were performed to a necessary thickness, and the middle bone block was removed. During this sandwich osteotomy, we left a minimum of 7.5 mm below the mental foramen to preserve the mental/alveolar nerve route.
A distal bone segment was moved to complete the ideal profile and was fixed using plates and/or screws. Before fixation, bony stepping at the inferior border of the mandible body was cautiously ostectomized to establish a smooth jaw line.
In setback genioplasty, the anterior cortical bone was partially removed using a burr between the B point and Pog level. [See Figure, Supplemental Digital Content 2, which shows a schematic diagram of genioplasty combined with ASO. Osteotomy lines of maxillary ASO, mandibular ASO, and genioplasty are illustrated. Oblique osteotomy line (c) for bony stepping following sandwich ostectomy is noted at the inferior border of the mandible. Partial removal of anterior cortical bone between B point and Pog level (d) is indicated by the dotted line in the setback genioplasty diagram, http://links.lww.com/PRS/G330.]
Finally, immediate postoperative profile line and occlusion were assessed. Following hemostasis and irrigation, the periosteum was sutured using 3-0 Vicryl. The intraoral wound was sutured without a drain. Elastic plaster (Elatex; Alcare) was applied around the chin.
Landmarks are shown in Figure 1. A horizontal line was used to define an angle of 7 degrees clockwise with a line connecting the sella and nasion. The vertical line was perpendicular to the horizontal line, and the distance from four points (ie, Pog, Me, Pog′, and and Me′) to these two lines were measured (Fig. 2). The V-ceph (Vatech; Republic of Korea) program was used for cephalometry.
Fig. 2. Landmarks and linear measurements. S, sella; N, nasion; Pog, pogonion; Me, menton; Pog′, soft-tissue pogonion; Me′, soft-tissue menton; x axis (SN-7° line), a line angulated 7 degrees clockwise to the SN-line passing through the sella; y axis (S-perpendicular line), a line perpendicular to the x axis passing through the sella; Pog_x, the horizontal distance from Pog to the y axis; Pog_y, the vertical distance from Pog to the x axis; Me_x, the horizontal distance from Me to the y axis; Me_y, the vertical distance from Me to the x axis; Pog′_x, the horizontal distance from Pog′ to the y axis; Pog′_y, the vertical distance from Pog′ to the x axis; Me′_x, the horizontal distance from Me′ to the y axis; Me′_y, the vertical distance from Me′ to the x axis.
The horizontal movement of Pog and vertical movement of Me were determined by calculating T2 to T1 and T3 to T2 for each point and group, respectively. Initial soft-tissue thickness (calculated by the horizontal distance from Pog to the y axis to the horizontal distance from Pog′ to the y axis and the vertical distance from Me to the x axis to the vertical distance from Me′ to the x axis) were also determined to assess relationships to soft-tissue response. To assess intraexaminer reliability, all variables were reevaluated 1 month later by the same investigator. Because paired t tests indicated no significant difference between the two, the first set was used in further statistical analyses.
For Pog change analysis, G1 was excluded because there was almost no sagittal change. Regarding Me change, all groups were combined and analyzed followed by group assessment. The Shapiro-Wilk test was used for evaluation of normality of each variable. Analysis of variance and Kruskal-Wallis tests with the post hoc Bonferroni correction method were then used to compare the values of each group. Paired t tests and Wilcoxon tests were performed to compare the values by period. Correlation analysis was performed to evaluate relationships between hard-tissue and soft-tissue response, along with initial soft-tissue thickness and soft-tissue response. Linear regression analysis was used to calculate the soft- to hard-tissue ratio in R (4.0.3).
Genioplasty was performed with ASO in 62 patients without any major complication. The surgical results after 2 months and 1.5 years are presented in Figures 3 and 4. (See Figure, Supplemental Digital Content 3, which shows a frontal view of a 30-year-old man with bimaxillary dentoalveolar protrusion who underwent height reduction genioplasty without sagittal change combined with ASO, http://links.lww.com/PRS/G331. See Figure, Supplemental Digital Content 4, which shows a frontal view of a 29-year-old woman with bimaxillary prognathism and macrogenia who underwent setback and height reduction genioplasty combined with ASO, http://links.lww.com/PRS/G332.)
Fig. 3. Lateral views of a 30-year-old man with bimaxillary dentoalveolar protrusion who underwent height reduction genioplasty without sagittal change combined with ASO (see Figure, Supplemental Digital Content 3, http://links.lww.com/PRS/G331). (Above, left) Preoperative photograph. (Above, center) Postoperative photograph at 2 months. (Above, right) Postoperative photograph at 1 year 5 months. (Below, left) Preoperative cephalometry. (Below, center) Postoperative cephalometry at 2 months. (Below, right) Postoperative cephalometry at 1 year 5 months.
Fig. 4. Lateral views of a 29-year-old woman with bimaxillary prognathism and macrogenia who underwent setback and height reduction genioplasty combined with ASO (see Figure, Supplemental Digital Content 3, http://links.lww.com/PRS/G332). (Above, left) Preoperative photograph. (Above, center) Postoperative photograph at 2 months. (Above, right) Postoperative photograph at 1 year 6 months. (Below, left) Preoperative cephalometry. (Below, center) Postoperative cephalometry at 2 months. (Below, right) Postoperative cephalometry at 1 year 6 months.
Table 1 shows variables according to the groups before treatment. After the Shapiro-Wilk test, either the analysis of variance or Kruskal-Wallis test was performed. Values of P < 0.05 were found for all eight variables, and post hoc analysis determined that there was no significant difference between G1 and G2, whereas G2 and G3 differed in every factor except the vertical distance from Me to the x axis, and G1 differed from G3 at the horizontal distance from Pog to the y axis, the horizontal distance from Me to the y axis, the vertical distance from Me to the x axis, the horizontal distance from Pog′ to the y axis, and the horizontal distance from Me′ to the y axis.
Sagittal changes at Pog for G2 and G3 are shown in Table 2. During the T1 to T2 period, Pog_x moved 3.56 mm in G2 and 4.7 mm in G3. the horizontal distance from Pog′ to the y axis moved 2.85 mm in G2 and 4 mm in G3. A “stable” procedure is defined by changes at landmarks less than 2 mm,^21^ and all changes we observed during the T2 to T3 period were within this range. Paired t tests were performed to observe changes in hard tissue, soft tissue, and soft-tissue thickness. Table 3 shows vertical changes at Me and Me′. At T1 to T2, Me moved 4.60 mm and Me′ moved 2.26 mm; soft-tissue thickness increased by 2.34 mm. At T2 to T3, there was no meaningful change.^21^ Paired t and Wilcoxon tests were used to evaluate changes of variables concerning Me.
The linear regression formulas for the hard-tissue and soft-tissue response are in Figure 5. The soft- to hard-tissue ratios defined by the slope of the formula were 0.85, 0.80, and 0.90 in G2 Pog, G3 Pog, and Me, respectively. Correlations between hard-tissue response and soft-tissue response and the initial soft-tissue thickness and soft-tissue response were identified both at Pog and at Me (Tables 4 and 5). The Pearson correlation test was performed first, followed by the Spearman correlation test for those with nonsignificant results from the Pearson test, and the results were similar. The correlation coefficients between osseous and soft-tissue response were 0.64 in G2 and 0.83 in G3. At Me of the combined groups, the value was 0.89; individual values for each group were 0.85 (G1) and 0.94 (G3). In G2, vertical osseous and soft-tissue change was not associated. The only meaningful correlation coefficient between initial soft-tissue thickness and soft-tissue response ratio was 0.49 in G3 Pog.
Fig. 5. The linear regression equations of hard- to soft-tissue response. (Left) Pog, G2: y = 0.85x − 0.06; R^2^ = 0.41; P < 0.01. (Center) Pog, G3: y = 0.80x − 0.05; R^2^ = 0.69; P < 0.01. (Right) Me, for all y = 0.90x + 1.88; R^2^ = 0.80; P < 0.01.
Genioplasty is known as a stable surgical procedure.^1–11,22–25^ Various topics about genioplasty have been well studied combined with other operations, bone-cutting devices, or allografts.^22–25^
As for the surgical planning and technique, first, we used cephalometric analysis because we do not believe that three-dimensional modalities are always superior to two-dimensional analysis. Second, we readjusted the amount of ASO movements by burring if necessary, within the range of proper occlusion based on the wafer. Third, we did not use customized fixation devices but rather microplates bent by the surgeon. Fourth, the surgeon discussed chin shape in depth with patients before surgery, and we regulated chin position and length by checking the intraoperative profile view. Fifth, dissection on the distal bone was restricted except for the fixation area. We did not use the degloving technique to prevent chin soft-tissue deformity. Zhang et al. also asserted that witch’s chin and soft-tissue ptosis can be decreased by no-degloving technique.^26^
Sixth, the routes of the alveolar and mental nerves were checked carefully by radiography. The hairpin shape of the alveolar nerve ending must be especially prudently examined before surgery. We left a minimum of 7.5 mm for a safe distance zone below the mental foramen. Lin et al.^27^ observed risk probabilities of 2.5%, 0.5%, and 0.0005%, respectively, in osteotomies 7.06, 8.01, and 9.12 mm below the mental foramen.^27^
Seventh, during closure, the periosteum was surely sutured layer by layer at two or three points to prevent ptotic displacement of the mentalis muscles, as Zide emphasized.^28^
Redraping of soft tissue without ptosis is especially important at the labiomental fold, which could be reinforced by pressure dressing using elastic plaster (Elatex) for 5 days, and a facial support band for a few weeks if necessary.
All changes during the retention period were not significant, indicating good stability of genioplasty with ASO. There was soft-tissue thickening at Me′ during T1 to T2, but no change of Pog′ in the setback group, unlike previous reports.^29,30^ The soft- to hard-tissue ratio in G3 Pog and Me was high compared with values reported previously.^16^ When the chin was set back, there should have been more soft-tissue movement because the vertical reduction of the chin itself has the effect of moving soft tissue forward.^30,31^ This indicates that setback genioplasty was optimally performed in unfavorable conditions. Correlations between soft-tissue and skeletal tissue response at Pog (advance), Pog (setback), and Me were studied simultaneously (Table 6). The correlation coefficients of horizontal movement in G3 and vertical movement in all patients were statistically significant, contrary to other reports.^1,6,29–34^ These results provide a good reference for surgical planning, and our null hypothesis was rejected.
To encourage soft tissue to follow hard-tissue movement, soft-tissue attachment to the bone segment was important in G2, as reported previously,^5,7,8,19,20,35^ whereas removing part of the anterior cortical bone was crucial in G3. A positive correlation was previously found between amount of vertical chin movement and change of soft-tissue thickness,^36^ but we observed no correlation between initial soft-tissue thickness and soft-tissue response rate in this study. This result is inconsistent with the hypothesis that the thinner the soft tissue is, the more likely it is to follow hard-tissue movement, as reported previously in a study finding that the lip followed incisors more in patients with thin lips compared with thick lips in orthodontic treatment.^37^
There are a number of possible explanations for this result. First, soft tissue is attached strongly to bone by the periosteum, unlike the lip to the teeth. The second is differences in elasticity between patients. Finally, the results might have been different if the sample size was larger.
Genioplasty accompanied by ASO provides several extraordinary conditions. First, in microgenia, ASO lessens the necessity and amount of chin advancement, as it produces a relative effect of chin advancement. Therefore, the amount of chin advancement was less than 4 mm in most of our cases. Second, the chin horizontal osteotomy line must be at least 3 mm lower than the horizontal osteotomy line for mandibular ASO, so the chin horizontal osteotomy line was lower compared with sole genioplasty cases. Therefore, osteotomized distal chin segments were usually smaller than in ordinary cases of sole genioplasty, which might have altered the prediction of soft-tissue response.
Most bimaxillary dentoalveolar protrusions are accompanied by microgenia or pseudomicrogenia. Minor cases of bimaxillary protrusion show macrogenia, which can be described as bimaxillary prognathism. If setback genioplasty can be performed effectively, some cases of bimaxillary prognathism can be treated using ASO instead of two-jaw surgery. Zide et al. elaborated key points for treating large chins.^38^ In our macrogenia cases, not only setback genioplasty but also setback of the B point (by mandibular ASO) was effective to achieve a natural labiomental contour. More intensive study is ongoing in a larger number of cases. Our results suggest that setback genioplasty with ASO has several advantages. The patients feel more comfortable and recover faster following ASO compared with two-jaw surgery. The lethality of two-jaw surgery is also higher than that of ASO, possibly because of the deeper surgical field, longer operation time, higher possibilities of hemorrhage at Le Fort and mandible ramus osteotomy sites,^39^ and the possibility of airway problems because of postoperative intermaxillary fixation in two-jaw surgery. No change or narrowing of the airway occurred postoperatively in any of our ASO cases, as seen in Figures 3 and 4.
Park et al.^29^ reported a ratio of 0.68 at Pog following two-jaw surgery with setback genioplasty, which was relatively low. Although the amount of chin setback using genioplasty without mandibular ramus osteotomy is limited, if we maximize the ratio at Pog, setback genioplasty with ASO could be used instead of two-jaw surgery in some cases of bimaxillary prognathism with macrogenia. Maximal chin reduction (Pog′_x) was 11.8 mm in our setback genioplasty cases, which was sufficient to improve macrogenia.
The importance of genioplasty cannot be overemphasized in almost all cases of ASO. Chin length and position are variable, as is maxillary/mandibular dentoalveolar position. This explains why there are few cases in which ASO without genioplasty produces an ideal profile. Vertical reduction of chin length is frequently necessary with ASO because ASO itself makes the chin appear longer than before.
Following setback genioplasty, the distance between the hyoid bone and Me inevitably lessens, which induces the possibility of submental soft-tissue excess. In addition, the submental skin appears saggy as Me moves up after height reduction genioplasty. Skin, subcutaneous tissue, and partially severed geniohyoid muscles are considered to be related, even though we do not use the degloving technique. This possibility of soft-tissue excess should be communicated to patients before surgery. Longer application of the facial support band can be helpful,^40^ and secondary soft-tissue tightening procedures might be necessary.
We analyzed two-dimensional data using cephalometry. We consider two-dimensional imaging to be flawless for the assessment of sagittal and vertical hard- and/or soft-tissue movements. However, further studies using three-dimensional software with more informative data are required.
Incomplete standardization of clinical photographs in terms of background and body orientation in lateral view is another shortcoming. Head positions of serial cephalograms also require refinement for standardization, although they were compensated for by the horizontal reference line (SN to 7 degrees).
The patient population was made up of East Asian patients only. This may be another limitation for generalizing our results.
Genioplasty is efficient when combined with ASO for the correction of microgenia/macrogenia in bimaxillary protrusion/prognathism without recurrence or major complications. Linear regression analysis showed a high soft- to hard-tissue ratio both in horizontal and in vertical chin movement. High correlations between hard- and soft-tissue response indicate the reliability of the soft- to hard-tissue ratios. However, no correlation was found between initial soft-tissue thickness and soft-tissue response ratio. The setback group showed distinct results among patient groups, implying that setback genioplasty with ASO is an effective alternative to two-jaw surgery in some cases of bimaxillary prognathism with macrogenia.
None of the authors has a financial interest in any of the products, devices, or drugs mentioned in this article.
Patients provided written informed consent for the use of their images.