Where to position osteotomies in genioglossal advancement surgery based on locations of the mental foramen, canine, lateral incisor, central incisor, and genial tubercle

What is the angular accuracy of regional voxel-based registration for segmental Le Fort I and genioplasty osteotomies?

Among the accuracy analysis techniques for orthognathic surgery, regional voxel-based registration (R-VBR) has robust data, but remains unvalidated for smaller jaw segments. The purpose of this study was to validate the angular accuracy of R-VBR for segmental Le Fort I (SLFI) and genioplasty osteotomies. Postoperative cone beam computed tomography (CBCT) of consecutive patients with three-piece SLFI or genioplasties was rotated to a known pitch/roll/yaw (P/R/Y). Using R-VBR, a copy of the raw CBCT was superimposed onto the rotated CBCT at four mutual regions of interest (ROI): anterior, right posterior, and left posterior maxilla, and chin. The P/R/Y of each was subtracted from those of the rotated CBCT to calculate the angular error. The predictor and outcome variables were ROI and absolute angular error, respectively. The accuracy threshold was 0.5°. Ten SLFI and 34 genioplasties were analyzed based on the sample size calculation. The one-sample t-test and Wilcoxon signed rank test were applied in the analysis. The mean absolute error was 0.20-0.54° for the maxillary segments (all P ≤ 0.01) and 0.83-2.51° for the genioplasty segments (all P < 0.001). R-VBR has variable angular accuracy for SLFI osteotomies and may be insufficient for genioplasty. The findings may allow the design and interpretation of studies on SLFI and genioplasty with greater rigor, thereby contributing to minimizing the discrepancy between planned and achieved outcomes.

3D Genial Tubercle Anatomic Considerations in Genioglossus Advancement Surgery

OBJECTIVE

To qualitatively describe variation in morphology of the genial tubercle and quantify the spatial relationship between the tubercle and genioglossus muscle.

STUDY DESIGN

Case series.

SETTING

Cadaver dissection.

METHODS

Segmental sections of the mandible, with muscular attachments intact, were harvested from 18 fresh cadaver heads. Three-dimensional laser scans, with a resolution of 0.025 mm, were taken of each specimen with muscle attached and repeated after muscle removal. The genioglossus muscular attachment was measured relation to bony landmarks.

RESULTS

The morphology of the genial tubercle varied, with anywhere from 1 large spine to 4 individual spines. However, all specimens had a distinguishable superior portion of the tubercle, where the genioglossus attached, and an inferior portion, where the geniohyoid attached. The height of the superior tubercle (ST) was 6.1 mm (95% confidence inerval [CI]: 5.7-6.5). The height of the genioglossus muscle above the peak amplitude of the ST was 4.3 mm (3.8-4.9), but only 2.5 mm (2.0-3.0) below. On average, 64.4% (58.6-70.2) of the height of the genioglossus muscle attachment was above the peak. Overall, 19.5% (14.1-25.0) of the muscle surface area extended beyond the boundaries of the tubercle.

CONCLUSION

The genioglossus muscle attachment originates from the superior genial tubercle, which has a variable topography and amplitude. However, the muscle is not centered on the spines-more of the muscular fibers attach above the spine as compared to below. This new data may explain the genioglossus advancement "miss rate"-failure to advance muscle on initial osteotomy-of 39-78% reported in the literature.

Morphometric aspects and proposal of a new classification of genial tubercles in cone-beam computed tomography in a Brazilian population

Objective

This study evaluated epidemiological and morphological aspects of genial tubercles (GTs) using cone-beam computed tomography (CBCT).

Methods

This retrospective, observational and cross-sectional study evaluated 276 tomographs of adult dentate individuals (18–69 years). The presence and absence of GTs were evaluated, and in cases in which this structure was observed, linear measurements (length, height, and width), and anatomical distances. In addition, a GT classification was proposed based on the presence, number, and location of the tubercles.

Results

Of the 276 CT scans, 28 (10.14%) had absence of GTs and in 248 CT scans GTs were present, of which 42 (57.5%) were from females and 106 (42.5%) from males. Regarding the number of GTS, the most prevalent variant was the two-tubercle-variant (143, 57.7%), followed by the presence of a single tubercle (n = 62, 25.0%), 3 tubercles (n = 40, 16.1%) and 4 tubercles (n = 3, 1.2%). The most prevalent classification was IIIA (n = 96, 38.7%), followed by IIIB (n = 60, 36.3%), IIA (n = 53, 21.4%) and IIB (n = 9, 3.6%).

Conclusion

A prevalence of GT of approximately 90% was observed, with two GTs per exam as the most frequent finding. Men had a longer mean GT length compared to women. Female individuals exhibited a shorter distance from the base of the GT to the base of the mandible.

A Modified Cosmetic Genioplasty Can Affect Airway Space Positively in Skeletal Class II Patients: Studying Alterations of Hyoid Bone Position and Posterior Airway Space

BACKGROUND

Improving the posterior airway space is one of the most important functions of genioplasty. Studies have shown that the posterior airway space (PAS) can play an important role in the evaluation of obstructive sleep apnea syndrome (OSAS). The purpose of this study is to evaluate the airway safety of our modified technology by observing the impact on PAS in skeletal Class II patients without OSAS.

METHODS

We have modified a cosmetic genioplasty, which can guarantee the continuity of the lower edge of the bilateral mandible by rotating the chin segment clockwise. Fourteen patients submitted to our modified cosmetic genioplasty alone were included in the study. The facial convexity angle and the ratio of the face were measured by analyzing photographs. The position of the hyoid bone and the width of the PAS were measured by analyzing lateral cephalograms. The volume and the cross-sectional area (CSA) of the PAS were measured using 3D reconstruction. The Wilcoxon signed-rank test and paired samples t test were used to assess the significance of differences of the data (p < 0.05).

RESULTS

Soft tissue measurements were statistically different (p = 0.001) and achieved satisfactory results. The position of the hyoid bone moved up (L_X: p = 0.004; L_ML: p = 0.056) and forward (L_Y: p = 0.001; L_CV3: p = 0.016). The increase in the CSA had statistical significance (p < 0.005). There were significant statistical differences in the total airway volume and hypopharynx (p = 0.001), except in the oropharynx (p = 0.096).

CONCLUSIONS

Our modified genioplasty not only achieved better cosmetic results by ensuring the continuity of the lower edge of the bilateral mandible but also exerted a significant positive impact on the posterior airway space for patients with skeletal class II, thus helping reduce the prevalence of OSAS. We hence suggest performing this modified cosmetic genioplasty on the skeletal class II patients with/without OSAS if necessary.

LEVEL OF EVIDENCE IV

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