|Year : 2019 | Volume
| Issue : 7 | Page : 891-896
Selection of ideal pterygoid osteotome: A preliminary study
O Odabasi1, N Moharamnejad2, O Sahin3
1 Department of Oral and Maxillofacial Surgery, Dentistry Faculty, Ankara Yıldırım Beyazıt University, Ankara, Turkey
2 Department of Oral and Maxillofacial Surgery, Dentistry Faculty, İstanbul Aydın University, İstanbul, Turkey
3 Department of Oral and Maxillofacial Surgery, Faculty of Dentistry, İzmir Katip Çelebi University, İzmir, Turkey
|Date of Acceptance||07-Mar-2019|
|Date of Web Publication||11-Jul-2019|
Department of Oral and Maxillofacial Surgery, İzmir Katip Çelebi University, Faculty of Dentistry, İzmir; Aydınlıkevler Mahallesi, Cemil Meriç Bulvarı, 6780 Sokak. No: 48, 35640-Çiğli/İzmir
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Background: Pterygomaxillary separation is the most critical step of Le Fort I osteotomy. Nonideal separation of pterygomaxillary junction could be associated with many complications. The purpose of this study was to evaluate the anatomic basis of proper pterygoid osteotome in Le Fort I surgery. Materials and Methods: The cone beam computed tomography image of 177 patients were evaluated retrospectively. To design an ideal osteotomy, the angle and the length of the posterior curvature of the maxillary sinus wall were measured. For the classification of the posterior angle as low, medium, and high, the category was based on upper and lower groups consisting of 27%, where the measurement and representability are at the maximum level. Results: The mean posterior length of three angle groups was as follows: low group: 7.81 mm, medium group: 7.54 mm, and high group: 7.41 mm. The differences were not statistically significant (P > 0.05). In addition, the posterior angle and length were evaluated according to the gender and the sides, and no statistically significant difference was found. (P > 0.05). Conclusion: Ideal osteotomy technique for pterygomaxillary disjunction and the avoidance of related complications could be achieved by selecting patient-specific osteotome using radiographic assessment.
Keywords: CBCT, fracture, Le Fort I osteotomy, pterygoid plate
|How to cite this article:|
Odabasi O, Moharamnejad N, Sahin O. Selection of ideal pterygoid osteotome: A preliminary study. Niger J Clin Pract 2019;22:891-6
| Introduction|| |
Le Fort I osteotomy is currently one of the most common surgical methods for correction of maxillofacial deformities. The debate about the mobilization of the maxilla has a long historical background. In 1942, Schuchardt had reported that the mobilization could be successfully implemented with the separation of the maxilla from the pterygoid process and suggested for the first time a pterygomaxillary separation method. Starting from this date, pterygomaxillary separation became a standard step of Le Fort I osteotomy., Pterygomaxillary separation is the most critical step of Le Fort I osteotomy. Serious complications such as severe hemorrhage, injury of the descending palatine artery, and injury of cranial nerve emerge as a result of pterygomaxillary separation procedure. Ideally, pterygomaxillary separation should go through the deepest part of the pterygomaxillary fissure (between maxillary tuberosity and pterygoid process, should not harm the integrity of the descending palatine artery and should not cause fractures of the pterygoid process. For the completion of this separation, several methods were described, but osteotomy is usually completed with the insertion of a curved and standard Obwegeser osteotome into the pterygomaxillary fissure with a blind approach., However, the examination of the pterygomaxillary region on the axial section revealed that the angle between the lateral and posterior walls of the maxillary sinus, where the osteotome will be inserted, and the length of the posterior wall of the maxillary tuberosity have rather different values. Starting from this point, the probable and important reason for the failure of an ideal separation during pterygomaxillary separation and thus the emergence of the complications may be osteotomy, which is carried out with standard osteotomes using a blind approach, which is not suitable to every patient's anatomy. The objective of this study was to investigate the curvature and the length of the posterior maxilla, anatomically and radiologically, which had not been carried out yet according to the literature search, and to provide an anatomic basis for the design of the ideally curved pterygoid osteotomes.
| Materials and Methods|| |
A total of 177 adult patients (86 females and 91 males) with Turkish ethnicity were included in the study. The mean age of the patients was 28.3 years (18–57 years). This study was approved by the ethical committee of our university. The inclusion criteria were as follows: (1) at least 18 years of age, (2) no defect and/or pathology in the posterior maxillary region, (3) absence of any previous operation of cyst or tumor in the posterior maxillary region, orthognathic surgical intervention, or trauma, and (4) cone beam computed tomography (CBCT) images of the patients without artifacts impairing the image quality.
In this study, a CBCT device (NewTom 5G(Ò), QR, Verona, Italy) was used, and the sections which contained images of the whole pterygoid process of the sphenoid bone and maxilla at axial sections and fields of views of 20 × 10 or 20 × 17 cm of the patient were acquired.
To standardize the image for measurement, methods, which were used in some previous studies, were modified., Primarily, the patient's head was positioned at the coronal plane, while the guiding line went through the middle of the anterior nasal spine [Figure 1]. Thereafter, Frankfurt horizontal plane was positioned parallel to ground plane at the sagittal plane. Then, two guide points were marked on this section [Figure 2].
|Figure 1: Positioning of the sagittal guide line at the coronal plane passing through the middle of the anterior nasal spine|
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|Figure 2: Insertion of the guide points on the sagittal plane for evaluation on the axial plane|
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On the axial plane, the images were evaluated while the axial guide line was positioned between these two guide points and the measurement was done in the section, where the parameters were best observed in the pterygomaxillary region [Figure 3].
|Figure 3: Selection of the section with clearest images of the pterygomaxillary region and with positioning between the previously determined guide points at the axial plane|
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The following parameters were evaluated on the obtained sections:
- Posterior angle: The angle between the line which has the longest contact to the lateral wall of the maxillary sinus (L line) and the line which has a broad contact to the maxillary tuberosity starting from the deepest point of the pterygomaxillary fissure (P line).
- Posterior length: The distance between the deepest point of pterygomaxillary fissure and the junction point of lines P and L [Figure 4].
|Figure 4: L line: The line with the longest contact to the lateral wall of the maxillary sinus. P line: The line which starts from the deepest point of the pterygomaxillary fissure and has a broad contact to the maxillary tuber|
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Posterior angle and posterior length measurements of the images obtained from 177 patients (354 sides) were analyzed using Statistical Package for the Social Sciences (SPSS 21.0; SPSS Inc., Chicago, IL, USA). For the classification of the posterior angle as low, medium, and high, the category was based on upper and lower groups consisting of 27%, where the measurement and representability are at the maximum level. In this context, according to the cumulative frequency, the lower 27% segment was classified as low level, the upper 27% segment as high level, and the remaining middle 46% segment as medium level. According to the angle classifications, the difference between the posterior lengths was evaluated with one-way analysis of variance method. The difference between the left and right posterior lengths and the difference between the left and right angles were analyzed with paired samples T-test. The difference between the angle and length measurements according to the patient's gender was investigated with independent samples T-test.
| Results|| |
The minimum and maximum values of the patient's posterior angle were 100° and 180°. The mean posterior angle was 134.45° on the right side and 134.43° on the left side, and there was no significant difference between the sides (P > 0.05) [Table 1]. The total posterior angle data of the 354 sides were classified into three groups as low, medium, and high according to cumulative distribution. Thus, the mean values of low, medium, and high groups were 120.90° (100°–127°), 133.92° (128°–140°), and 149.77° (141°–180°), respectively. This classification was done for both the left and right sides [Table 2]. The classification of the posterior angles according to the gender showed that the mean value of the posterior angles was 135.4° in women and 133.46° in men. The difference was not statistically significant (P > 0.05) [Table 3].
|Table 2: Classification of posterior angles according to the upper and lower groups consisting of 27% analysis|
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The posterior length was 7.59 mm on the left side and 7.53 mm on the right side and there was no significant difference between them (P > 0.05) [Table 1]. Regarding the right side, it was 7.81 mm in men and 7.23 in women, and regarding the left side, it was 7.77 mm in men and 7.38 mm in women. The differences were not statistically significant [Table 3]. The mean posterior length of three angle groups was as follows: low group: 7.81 mm, medium group: 7.54 mm, and high group: 7.41 mm. The differences were not statistically significant. There was a weak correlation between the posterior angle and posterior length bilaterally (P > 0.05) [Table 4].
|Table 4: Analysis of the relationship between posterior angle and length|
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| Discussion|| |
Although Le Fort I osteotomy is frequently used for the treatment of dentofacial deformities, it is also preferred for the surgical treatment of the cysts and tumors, as it enables an easy access to the nasal fossa, paranasal sinuses, and nasopharyngeal region.,,
Several studies showed that the complication rates related to Le Fort I osteotomy were between 6.1% and 9.0%. Most of these complications are transient and not life-threatening and do not cause permanent damage. However, serious complications such as cranial nerve injuries causing permanent blindness and paralysis, aseptic necrosis, severe bleeding, and even death may occur in rare cases.,
The preservation of the integrity of these vital structures is very important during the pterygomaxillary osteotomy regarding the prevention of the above-mentioned complications.
The pterygomaxillary osteotomy is the most critical step of Le Fort I osteotomy due to the closeness of some important anatomic structures to the operation site and the blind approach to the subperiosteal tunnel. During the implementation of this osteotomy, a curved Obwegeser osteotome is usually placed in the pterygomaxillary fissure using a blind approach. Besides this, some modified osteotomes called “swan neck” and “shark fin” were also described. Precious et al. developed a method to implement pterygomaxillary separation without the use of osteotome. According to a survey, which was conducted with 175 maxillofacial surgeons in the United Kingdom in 2004, 85% of the surgeons used an osteotome for the separation of the posterior maxilla and 78% of them performed osteotomy from the pterygomaxillary region and 7% from the maxillary tuberosity.
An ideal pterygomaxillary separation should be carried out between maxillary tuberosity and pterygoid process. During this procedure, the descending palatine canal should not be damaged and the integrity of the laminae of the processus pterygoideus and its adhesion to the cranial base should be preserved., Precious et al. evaluated the results of pterygomaxillary separation procedures, which they carried out with and without osteotome, with the postoperative CT analysis. They concluded that an ideal separation could be achieved only in 27% of the pterygomaxillary regions without osteotome and in 29% with osteotome. Robinson and Hendy  conducted a study on cadavers and observed pterygoid process fractures in 75% of separation procedures done with a standard curved pterygoid osteotome.
Some investigators tried an anterior approach to improve the outcome of the intervention. Trimble et al. performed osteotomy 0.5–1 mm above the crest, over the maxillary tuberosity and at the distal of the second molar without any incision. On the other hand, Stajčić recommended the implementation of pterygomaxillary separation with a large angulation (80° at the sagittal plane) of the pterygoid osteotome toward the lateral following a straight vertical incision in the pterygomaxillary region. The investigator experimented this method on fresh cadavers and he detected fractures in 9 of the 12 osteotomy fields with an osteotome angulation of 50° and in 5 of the 12 osteotomy fields with an osteotome angulation of 80°. In our study, we showed that the osteotomy angle should have very different values for an ideal separation, and an extensive angulation of the tip of the osteotome toward lateral at the sagittal plane was required, as recommended by Stajčić. However, too much angulation of osteotome manually under the subperiosteal tunnel may cause mucosal tearing. Besides this, if a vertical incision is done in the pterygomaxillary region, as recommended by some authors, pterygoid vein plexus may be damaged and the cheek tissue will not allow an angulation of 80°. Considering these limitations, the angulation of the tip of osteotome is a more appropriate option and this was the osteotomy technique recommended by Trimble et al., which performed from the tuberosity region preserves the integrity of the pterygoid plates. However, bone removal from the posterior region will become more complicated in maxillary setback surgery. In addition, it is quite difficult to determine a definitive anatomic landmark and angulation with a straight osteotome used in this method.
Our study showed that the usage of a single standard curved pterygoid osteotome for the separation of the pterygomaxillary region of patients, which can have different depths and curvatures [Figure 5], will not be effective. Therefore, the posterior angle values were divided into three groups according to the cumulative frequency values for the design of the osteotome suitable to patients' anatomy and the mean values of the groups were calculated. Osteotome specific to a patient, which is produced according to the three types of angulation (120.90°, 133.92°, and 149.77°), can be selected depending on the results of CBCT evaluation, and thus nonideal separations and complications can be prevented.
|Figure 5: Pterygomaxillary regions with different angles and posterior lengths. Low angle group on the left, high angle group on the right|
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Regarding an ideal osteotome, the length of the blade is another important factor [Figure 6], as the osteotome should engage completely the width of the pterygomaxillary region. To meet this requirement, the length of the blade should be at least – with a simple calculation – equal to the sum of the width of the pterygomaxillary region and the posterior length, which we measured in our study. In their study, Ueki et al. found out that the width of the pterygoid process was 7.7 mm on the right side and 7.6 mm on the left side. The width was on the right and left sides of the control group was 8.6 and 8.5 mm, respectively, and in patients with cleft lip 9.9 and 9.8 mm, respectively. The mean width of the pterygomaxillary region measured by Hwang et al. was 8.01 mm, and they proved on the postoperative CT images that the decrease in this distance was a risk factor for pterygoid process fractures. The length of an ideal osteotome should cover the posterior length along with pterygomaxillary width. In our study, the posterior length was 7.53 mm on the right side and 7.59 mm on the left side. Taking individual variations into consideration, the length of the osteotome should be 20–25 mm.
The most important reference regarding the length of the osteotome is the study conducted on cadavers by Turvey and Fonseca. According to the results of this study, the mean vertical height of the pterygomaxillary suture was 14.6 mm (11–18 mm) and the mean distance between the lowermost of the junction of the maxilla and the pterygoid process and the maxillary artery is 25 mm (23–28 mm). Depending on the results of this study, it was recommended that the width of the osteotome (height at the vertical plane) should be 10 mm and a safety space about 10–15 mm between the uppermost point of the osteotome and the artery should be preserved to avoid maxillary artery injuries.
| Conclusion|| |
We conclude that the design of the osteotomes according to the data obtained in this study is quite important for the selection of an instrument suitable for patients with examination of preoperative CBCT images for prevention of complications. According to our study, three angles (120.90°, 133.92°, and 149.77°) were recommended for the curved osteotomes. These osteotomes should be placed as close as possible to the lateral wall of the maxillary sinus in order not to cause any retraction in the buccal tissues and to eliminate any need for a larger incision. To separate the pterygomaxillary junction completely, the recommended length of the blade of the osteotome should be between 20 and 25 mm and the width should be 10 mm.
Our study is the first evaluation of the angle of the junction between the maxilla and the pterygoid process, and the lack of a clinical confirmation of the recommendations was the limitation of the study. The objective of future research should be evaluation of three-dimensional finite element analysis with clinical and anatomic studies in different ethnic groups and with larger sample sizes to confirm the results of our study.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
[Table 1], [Table 2], [Table 3], [Table 4]