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Cone beam computed tomography assessment of the pterygomaxillary region and palatine canal for Le Fort I osteotomy
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Int. J. Oral Maxillofac. Surg. 2017; xxx: xxx–xxx http://dx.doi.org/10.1016/j.ijom.2017.03.030, available online at http://www.sciencedirect.com
Clinical Paper Orthognathic Surgery
Cone beam computed tomography assessment of the pterygomaxillary region and palatine canal for Le Fort I osteotomy
G. Q. V.Oliveira1, M. A. Rossi2, T. V. Vasconcelos3, F. S. Neves1, I. Crusoe´-Rebello1 1 Division of Oral Radiology, School of Dentistry, Federal University of Bahia, Canela, Salvador, Bahia, Brazil; 2Department of Biomorphology, Division of Anatomy, Health Science Institute, Federal University of Bahia, Canela, Salvador, Bahia, Brazil; 3Department of Preventive Dentistry, Division of Oral Radiology, School of Dentistry, Federal University of Pernambuco, Cidade Universita´ria, Recife, Pernambuco, Brazil
G. Q. V. Oliveira, M. A. Rossi, T. V. Vasconcelos, F. S. Neves, I. Crusoe´-Rebello: Cone beam computed tomography assessment of the pterygomaxillary region and palatine canal for Le Fort I osteotomy. Int. J. Oral Maxillofac. Surg. 2017; xxx: xxx–xxx. ã 2017 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Abstract. The aim of this study was to evaluate the anatomical linear measurements of the descending palatine canal and the pterygomaxillary fissure for Le Fort I preoperative planning. Seventy-five patients, comprising 46 females (61.3%) and 29 males (39.7%), underwent multi-slice computed tomography examinations performed for preoperative orthognathic surgical planning. The images were categorized according to sex, craniofacial side, and skeletal and craniofacial patterns. The anterior length between the descending palatine canal and the lateral wall of the piriform rim showed a higher mean value for males compared to females (P = 0.0121). The posterior distance also showed a difference between the sexes and the highest mean was observed in females (P = 0.0295). Comparing the posterior width for the skeletal patterns, a statistical difference was observed between classes I and III (P = 0.0371), and classes II and III (P = 0.0094). Regarding the craniofacial patterns, the brachycephalic (P = 0.0078) and mesocephalic (P = 0.0015) groups showed a greater posterior width in females. In conclusion, the patient’s sex and aspects of the skeletal pattern and craniofacial pattern have an influence on the pterygomaxillary area and descending palatine canal anatomy. A preoperative computed tomography analysis involving this evaluation could reduce the risk of surgical complications.
Computed tomography (CT) images, along with virtual surgical preoperative planning, are important tools when performing surgical procedures. These tools potentially add new information to aid in 0901-5027/000001+07
patient management and to improve the surgical technique1. The Le Fort I osteotomy is usually indicated for the surgical correction of dentofacial deformities. Medical profes-
Key words: Le Fort I osteotomy; maxillary artery; orthognathic surgery; computed tomography. Accepted for publication 23 March 2017
sionals can carry out procedures with greater safety by better understanding the anatomy of the maxillary blood supply, and by availing themselves of today’s improved approaches and instruments.
ã 2017 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Oliveira GQV, et al. Cone beam computed tomography assessment of the pterygomaxillary region and palatine canal for Le Fort I osteotomy, Int J Oral Maxillofac Surg (2017), http://dx.doi.org/10.1016/j.ijom.2017.03.030
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However, surgical complications, such as major haemorrhage or skull fractures, may occur as a consequence of bone manipulation, mainly in connection with pterygomaxillary dysjunction2–4. Manipulation of the posterior maxilla bone following Le Fort I osteotomy may be a challenging procedure due to limited visualization, the proximity to anatomical structures such as the descending palatine artery, and the location of the pterygomaxillary region. In this regard, previous studies have reported a variety of techniques that may protect against complications and reduce the risk of injury to the patient3,5–11. In addition, some authors have highlighted that osteotomy of the medial or lateral maxillary sinus walls, pterygomaxillary dysjunction, and downfracturing of the maxilla must be performed with caution, since major bleeding from injuries to the descending palatine artery during these procedures is the most common cause of intraoperative and postoperative complications7,12. Today, osteotomies for pterygomaxillary disarticulation and the complete separation of the maxillary sinus walls are procedures that are avoided9. These approaches may increase the risk posed by surgery and the consequent susceptibility to bone fracture, haemorrhage, optic nerve damage, and arteriovenous fistula. Thus, knowledge of the anatomy in association with the appropriate surgical technique is necessary to increase the safety of Le Fort I osteotomies. Previous studies have analyzed these factors in relation to different populations, such as those of the USA13, Thailand14, and Japan12. How-
ever, there have been no reports in relation to Brazilian patients and there is also no evidence of any correlation between these aspects and the craniofacial side, patient’s sex, and craniofacial morphology and patterns. Therefore, the aim of this study was to evaluate the anatomical linear measurements of the descending palatine canal and the pterygomaxillary fissure for Le Fort I preoperative planning, as well as to assess the effects of the craniofacial side (left and right), patient’s sex, and skeletal and craniofacial patterns.
Materials and methods
The design of this study was approved by the local research ethics committee of the University of Bahia Dental School. Seventy-five adult patients, comprising 46 females (61.3%) and 29 males (39.7%), underwent multi-slice computed tomography (MSCT) examinations, which were performed preoperatively for a random group of orthognathic surgery patients. Patients presenting syndromes, cleft lip and palate, signs of maxillary tumours, facial trauma or previous surgery, and reduced maxillary sinus development were excluded from the study. The MSCT images were acquired with a 64-slice system (Light Speed VCT; GE Healthcare Bio-Sciences, Piscataway, NJ, USA), using the same settings: 120 kV, 200 mA, and 32-cm field of view, including observation of the full craniofacial complex. The axial slice thickness was 0.6 mm.
Image analysis
The right and left sides of the patient were considered separately when performing the evaluation, thus the sample comprised 150 images. These images were assessed individually under dim lighting by one previously calibrated observer using Dolphin Imaging software (version 11.7, Premium; Dolphin Imaging and Management Solutions, Chatsworth, CA, USA). The images were adjusted to ensure a parallel Frankfort horizontal (FH) plane, in order to attain a standardized head position, using the frontozygomatic sutures as a reference for the frontal view and the orbital inferior margin as well as the porion landmark for the lateral view. The orbital floors were then aligned (Fig. 1). An axial reconstruction was selected from each dataset for evaluation and the acquisition of measurements at 3 mm above the nasal floor, in accordance with a method proposed previously by Ueki et al.12 (Fig. 2). The observer established the position of the descending palatine canal in this image, and a line was drawn parallel to the most concave point of the pterygomaxillary fissure (pterygomaxillary fissure line). The following measurements were then acquired, based on the method proposed by Ueki et al.12: (1) Measurement A: anterior length (the distance between the most anterior point of the descending palatine canal and the most anterior point of the lateral wall of the piriform rim) (Fig. 3A).
Fig. 1. Three-dimensional reconstruction—frontal and lateral views of the standardized head position.
Please cite this article in press as: Oliveira GQV, et al. Cone beam computed tomography assessment of the pterygomaxillary region and palatine canal for Le Fort I osteotomy, Int J Oral Maxillofac Surg (2017), http://dx.doi.org/10.1016/j.ijom.2017.03.030
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CBCT assessment for Le Fort I osteotomy
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Fig. 2. MCST reconstructions—axial reconstruction selected at 3 mm above the nasal floor.
(2) Measurement B: posterior length (the distance between the most posterior point of the descending palatine canal and the pterygomaxillary fissure line) (Fig. 3B). (3) Measurement C: width of the pterygoid plates (the narrowest width between the lateral and the medial pterygoid plates at the pterygomaxillary fissure line) (Fig. 3C). (4) Measurement D: depth of the descending palatine canal (the distance between the most lateral point of the pterygomaxillary fissure and the lateral portion of the descending palatine canal) (Fig. 3D). (5) Measurement E: diameter of the descending palatine canal (the distance
between the most anterior and the most posterior portion of the descending palatine canal) (Fig. 3E). (6) Measurement F: posterior width of the maxilla (the distance between the most posterior portion of the maxillary sinus and the most anterior point of the pterygomaxillary fossa) (Fig. 3F). (7) Measurement G: medial plate length (the shortest length between the pterygomaxillary fissure line and the most posterior point of the medial pterygoid plate) (Fig. 3G/H). (8) Measurement H: Lateral plate length (the shortest length between the pterygomaxillary fissure line and the most posterior point of the lateral pterygoid plate) (Fig. 3G/H).
The samples were divided into three groups according to the patient’s skeletal pattern assessed on a lateral cephalogram using Tweed’s classification, based on ANB measurements (the angle formed by point A, nasion, and point B) and the relationship between the jaws in sagittal view. Accordingly, 22 patients (29.3%) were classified as class I (ANB 0–4.5 ), 33 (44%) as class II (ANB >4.5 ), and 20 (26.7%) as class III (ANB <0 ). The sample was also classified into three groups based on the craniofacial pattern as described by Riedel in 1952, according to the NS–Go–Gn angle13: brachycephalic (<27 ), mesocephalic (27–37 ), and dolichocephalic (>37 ). Accordingly, 20 patients (26.7%) were
Fig. 3. Axial reconstructions and measurements: A: anterior length; B: posterior length; C: width of the pterygoid plates; D: depth of the descending palatine canal; E: diameter of the descending palatine canal; F: posterior width of the maxilla; G/H: medial plate length, lateral plate length, and pterygomaxillary fissure line.
Please cite this article in press as: Oliveira GQV, et al. Cone beam computed tomography assessment of the pterygomaxillary region and palatine canal for Le Fort I osteotomy, Int J Oral Maxillofac Surg (2017), http://dx.doi.org/10.1016/j.ijom.2017.03.030
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Table 1. General and side measurements means and standard deviation (SD) and measurements according to gender and side. Measurement
General Mean
Measurement A Measurement B Measurement C Measurement D Measurement E Measurement F Measurement G Measurement H
38.86(3.1) 2.64(1.3) 7.68(1.7) 5.07(1.6) 3.37(0.9) 2.96(1.4) 7.53(2.6) 12.17(3.2)
Side Mean Right Side
Left Side
Gender Male
Female
Right Side Male
Left Side Female
Male
Female
38.97 (3.1) 38.75(3.0) 39.79(3.2)* 38.55(2.9)* 39.88(2.9)* 38.40(3.1)* 39.70(3.4)* 38.14(2.7)* 2.70(1.2) 2.57(1.3) 2.39(1.2)* 2.85(1.3)* 2.55(1.2) 2.80(1.4) 2.28(1.3) 2.74(1.2) 7.72(1.7) 7.62 (1.8) 7.77(1.7) 7.61(1.8) 7.84(1.7) 7.65(1.8) 7.66(1.7) 7.60(1.7) 5.11(1.7) 5.01(1.6) 5.05(1.7) 5.07(1.6) 5.19(1.7) 5.06(1.7) 4.90(1.6) 5.08(1.4) 3.34(1.0) 3.40(0.9) 3.44(0.9) 3.32(0.9) 3.40(1.0) 3.30(0.9) 3.50(0.8) 3.34(0.9) 3.00(1.4) 2.92(1.5) 2.52(1.3)* 3.24(1.4)* 2.56(1.2)* 3.28(1.6)* 2.47(1.3)* 3.23(1.3)* 7.20*(2.7) 7.86*(2.4) 8.40(2.8)* 6.98(2.2)* 7.91(2.1)* 6.75(2.4)* 8.93(3.3)* 7.23(2.1)* 12.01(3.2) 12.33(3.2) 12.67(2.8)* 11.22(3.4)* 12.72(2.7) 11.55(3.3) 12.65(2.9) 12.13(3.4)
Measurement A. Anterior Length; Measurement B. Posterior Length; Measurement C. Width of the pterygoid plates; Measurement D. Depth of the descending palatine canal; Measurement E. Diameter of the descending palatine canal; Measurement F. Posterior width of the maxilla; Measurement G. Medial plate length; Measurement H. Lateral plate length. * Statistically significant (P < 0.05).
classified as dolichocephalic, 33 (44%) as mesocephalic, and 22 (29.3%) as brachycephalic. Statistical analysis
The data were analyzed using BioEstat (Mamiraua´ Institute, Bele´m, Brazil). The reproducibility was intra-observer assessed using the intra-class correlation coefficient (ICC), classified as perfect (0.81–1.0), substantial (0.61–0.80), moderate (0.41–0.60), fair (0.21–0.40), or poor (0.00–0.20). The pterygoid measurements were tested using one-way analysis of variance (ANOVA) with the post hoc Tukey test (skeletal and facial pattern) and the t-test (sex and jaw side), with the significance level set at P < 0.05. Results
The ICC values showed excellent intraobserver agreement (0.91–0.95) for all reevaluated measurements. The measurements are summarized in Table 1, according to the craniofacial side and sex. With regard to the side, a statistical difference was observed only for the medial plate length of the pterygoid process (P = 0.0072), with the left side showing a higher mean value. With regard to sex, the mean anterior length value was higher for males, with a statistically significant difference compared to females (P = 0.0121). Moreover, a statistically significant difference was also observed in males for both the right (P = 0.0397) and left (P = 0.0297) sides, compared to females. The posterior length (measurement B) also differed between the sexes (P = 0.0295), with the highest mean value observed in females. However, on analyzing the sides individually, no statistically significant differences were observed. The posterior width of the maxilla was greater in females (P = 0.0031),
and was also greater in females for the right (P = 0.0455) and the left (P = 0.0297) sides when evaluated individually (Table 1). The length of the pterygoid plates also showed difference between the sexes. In general, the measurement values were greater in males. The medial plate length differed significantly between the sexes (P = 0.0013), and also when the right (P = 0.0379) and left (P = 0.0085) sides were evaluated individually. Regarding the skeletal pattern, the anterior length (P = 0.0001) and the medial plate of the pterygoid process (P = 0.0175) were statistically larger in class II males than in class II females. In class I individuals, the lateral plate of the pterygoid process was statistically larger for males than for females (P = 0.0106). In class III individuals, the palatine canal presented a larger diameter (P = 0.0055) and depth in males (P = 0.0419). However, the posterior width of the maxilla was significantly larger in females (P = 0.0034) (Table 2). On comparing the skeletal patterns, class II and class III subjects presented a posterior width of the maxilla of 3.23 mm and 2.37 mm, respectively (P = 0.0094). Moreover, class I subjects presented a larger measurement mean than class III subjects (P = 0.0371). Considering each side individually, no statistical difference was observed between class I and class III subjects. Also, statistical difference between class I and III for medial plate length was found (P = 0.022). Regarding the class II group, the medial plate of the pterygoid process was found to be larger on the left side than on the right side (P = 0.0481) (Table 2). Regarding the craniofacial patterns, no differences were observed among the brachycephalic, mesocephalic, and dolichocephalic patterns, regardless of sex and side. However, in the brachycephalic
group, the posterior width of the maxilla was greater in females than in males (P = 0.0078), and the length of the lateral plate of the pterygoid process was greater in males (P = 0.0342). Analyzing the sides individually, the diameter of the palatine canal was significantly larger for the right side (P = 0.0206) (Table 3). The mesocephalic group presented a greater posterior width of the maxilla in females than in males (P = 0.0015). The medial plate of the pterygoid process was larger for males (P = 0.0147), and on comparing the sides, this measurement was significantly larger on the left side (P = 0.0152). The depth of the descending palatine canal in the mesocephalic group was greater for the right side (P = 0.0373) (Table 3). In dolichocephalic individuals, the anterior length was significantly greater for males (P = 0.0060), and also for the right side (P = 0.0275). Moreover, the diameter of the descending palatine canal was significantly larger on the left side (P = 0.0062) (Table 3). Discussion
It is difficult to assess some of the important structures, like the pterygomaxillary fissure and the palatine canal, during Le Fort I osteotomy. Because of the importance of these structures when performing the osteotomy, some studies have sought to correlate the anatomical parameters in the pterygomaxillary region11–13,15, with the aim of simplifying planning and surgical instrumentation in this region11. The maxillary osteotomy is considered a safe technique with a low rate of complications16, ranging from 6.1% to 9.1%17,18. Some of these complications may result from incorrect pterygomaxillary dysjunction and trauma to the structures contained in the palatine canal. It should be noted that anatomical variations
Please cite this article in press as: Oliveira GQV, et al. Cone beam computed tomography assessment of the pterygomaxillary region and palatine canal for Le Fort I osteotomy, Int J Oral Maxillofac Surg (2017), http://dx.doi.org/10.1016/j.ijom.2017.03.030
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Class
Measurements Measurement Measurement Measurement Measurement Measurement Measurement Measurement Measurement
A B C D E F G H
Class I
Class II
Class III
Class I
Class II
Class III
I
II
III
Male
Female
Male
Female
Male
Female
Right
Left
Right
Left
39.07(2.9) 2.65(1.3) 7.75(1.8) 5.12(1.8) 3.25(0.9) 3.09(1.6)¥ 7.00(2.5)* 11.80(3.2)
39.19(3.2) 2.60(1.2) 7.69(1.7) 5.07(1.5) 3.43(1.1) 3.23(1.5)* 7.37(2.3) 12.64(3.2)
38.08(2.9) 2.68(1.4) 7.55(1.8) 4.98(1.7) 3.41(0.8) 2.37(0.9)*,¥ 8.38(2.9)* 11.76(3.2)
39.47(3.2) 2.22(1.3) 7.95(1.6) 5.14(1.5) 3.29(1.1) 2.34(1.2) 7.26(2.5) 13.95(2.7)*
38.60(2.9) 2.82(1.3) 7.66(1.8) 5.15(2.1) 3.29(1.1) 3.38(1.9) 6.22(2.8) 10.97(2.7)*
42.18(2.7)* 2.50(1.0) 7.78(1.8) 4.73(1.9) 3.29(0.9) 3.49(1.5) 8.45(2.5)* 12.92(2.4)
37.91(3.3)* 2.57(1.5) 8.01(1.2) 5.17(1.1) 3.56(0.9) 3.15(1.7) 6.73(2.1)* 11.74(3.3)
38.58(2.6) 2.33(1.4) 8.00(1.8) 5.51(1.7)* 3.74(1.0)* 1.95(0.7)* 8.50(2.5) 11.44(2.8)
36.90(3.1) 3.31(1.4) 7.28 (2.0) 4.50(1.5)* 3.05(0.6)* 3.12(0.9)* 7.06(2.3) 11.43(4.2)
39.11(3.0) 2.69(1.3) 7.95(1.8) 5.33(2.0) 3.27(1.0) 2.98(1.7) 6.60(2.6) 11.79(3.0)
39.03(2.8) 2.61(1.3) 7.54(1.7) 4.92(1.5) 3.23(0.8) 3.20(1.6) 7.40(2.5) 11.86(3.4)
39.39(3.4) 2.73(1.3) 7.61(1.7) 4.96(1.5) 3.32(1.0) 3.39(1.6) 7.08(2.2)* 12.2(3.2)
38.99(3.2) 2.47(1.2) 7.78(1.7) 5.17(1.6) 3.53(1.1) 3.07(1.4) 7.66(2.4)* 13.09(3.1)
Right
Left
38.13(2.7) 2.67(1.4) 7.66(1.9) 5.11(1.7) 3.44(0.9) 2.39(0.9) 8.05(2.4) 11.93(3.3)
38.04(3.2) 2.69 (1.5) 7.45 (1.8) 4.86 (1.6) 3.37 (0.7) 2.35 (1.0) 8.72 (3.4) 11.58(3.3)
Measurement A. Anterior Length; Measurement B. Posterior Length; Measurement C. Width of the pterygoid plates; Measurement D. Depth of the descending palatine canal; Measurement E. Diameter of the descending palatine canal; Measurement F. Posterior width of the maxilla; Measurement G. Medial plate length; Measurement H. Lateral plate length. *,¥ Statistical significance (P < 0.05).
Table 3. Gender and side measurements mean and SD according to the craniofacial patterns. Craniofacial Pattern
Measurements
Brachycephalic Mesocephalic Dolicocephalic Measurement Measurement Measurement Measurement Measurement Measurement Measurement Measurement
A B C D E F G H
38.21(3.7) 3.13(0.9) 7.88(2.0) 5.17(1.8) 4.12(1.2) 3.11(1.75) 7.55(3.3) 10.9(4.2)
39.23(3.3) 2.73(1.5) 7.95(1.8) 5.44(1.7) 3.34(0.9) 3.02(1.7) 7.09(2.5) 12.31(3.0)
38.95(2.9) 2.58(1.3) 7.53(1.8) 4.84(1.7) 3.15(0.9) 2.97(1.4) 7.19(2.1) 12.04(3.0)
Brachycephalic
Mesocephalic
Dolicocephalic
Brachycephalic
Mesocephalic
Dolicocephalic
Male
Female
Male
Female
Male
Female
Right
Left
Right
Left
Right
Left
38.31(2.7) 3.13(1.2) 8.43(2.1) 5.68(1.8) 3.95(1.3) 2.25(0.5)* 7.90(3.7) 13.07(3.1)*
38.85(4.6) 3.38(1.0) 7.50(1.9) 4.92(1.9) 3.53(1.1) 4.23(1.7)* 7.78(2.8) 9.46(3.4)*
39.85(3.3) 2.30(1.2) 7.61(1.6) 5.15(0.3) 3.21(0.7) 2.21(1.0)* 8.44(2.2)* 12.91(2.7)
38.89(3.3) 2.79(1.4) 7.90(1.7) 5.43(1.6) 3.47(1.0) 3.47(0.3)* 6.70(2.5)* 11.51(3.4)
40.64(2.8)* 2.20(1.3) 7.80(1.7) 4.81(1.7) 3.50(0.9) 3.01(1.6) 8.23(3.1) 12.33(2.9)
38.28(2.4)* 2.49(1.3) 7.61(1.8) 5.07(1.5) 3.13(1.0) 2.88(1.7) 6.94(2.2) 11.60(2.9)
38.21(3.7) 3.13(0.9) 7.83(2.0) 5.17(1.8) 4.12(1.2)* 3.12(1.8) 7.55(3.2) 10.90(4.2)
38.32(3.8) 3.23(1.4) 7.87(1.9) 5.13(1.8) 3.36(0.9)* 3.14(1.4) 9.15(3.6) 11.74(2.9)
39.23(3.3) 2.73(1.5) 7.95(1.8) 5.44(1.7)* 3.34(0.9) 3.02(1.7) 7.09(2.5)* 12.31(3.0)
39.23(3.2) 2.64(1.4) 7.71(1.7) 5.01(1.5)* 3.34(0.7) 2.97(1.6) 7.71(2.5)* 12.23(3.4)
38.95(2.9)* 2.58(1.3) 7.53(1.8) 4.89(1.7) 3.15(0.9)* 2.97(1.4) 7.19(2.1) 12.04(3.0)
38.47(2.8)* 2.35(1.1) 7.49(1.7) 4.99(1.6) 3.45(1.1)* 2.84(1.2) 7.67(2.7) 12.54(3.4)
CBCT assessment for Le Fort I osteotomy
Measurement A. Anterior Length; Measurement B. Posterior Length; Measurement C. Width of the pterygoid plates; Measurement D. Depth of the descending palatine canal; Measurement E. Diameter of the descending palatine canal; Measurement F. Posterior width of the maxilla; Measurement G. Medial plate length; Measurement H. Lateral plate length. * Statistically significant (P < 0.05).
5
in this region such as an increased bone thickness or bone defects will predispose the individual to a relatively high risk of unfavourable pterygomaxillary dysjunction11. In performing an osteotomy of the lateral nasal wall, extreme caution should be taken to avoid damage to the palatine canal when separating the upper maxillary bone from the palatine bone. The descending palatine artery, contained in the palatine canal, is associated with a higher bleeding rate in Le Fort I osteotomy19. During this surgery, there is the risk of partial lesion to the descending palatine artery, evolving into aneurysm formation and bleeding in the postoperative period20. Thus, it is important to avoid the risk of this type of injury. For this reason, determining the anatomical parameters is relevant to the planning and execution of the osteotomy of the medial wall of the maxillary sinus. The present study showed that the anterior length (measurement A) was a mean 38.06 mm, with a minimum length of 30.90 mm and maximum length of 46.20 mm. Li et al. studied CT measurements and reported an average distance of 38.40 mm, ranging from 34 mm to 42 mm13. In a study on human dry skulls, Cheung et al. found a smaller average length (34.1 mm) than that found in the present study21. Their measurements also showed a wider range, with a minimum anterior length of 23.80 mm and a maximum length of 41 mm. This difference could be attributed to the greater proportion of class III individuals in the population (subjects of Asian origin). The evaluation of the individual sides revealed a mean length of 38.97 mm for the right side and of 38.75 mm for the left side, with no statistically significant difference between the sides. Ueki et al. also found no statistically significant difference between the sides and reported average values similar to those of the present study (39.1 mm for the right side and 39.4 mm for the left)12. Injuries to the descending palatine artery during Le Fort I osteotomy can be minimized when osteotomy of the lateral nasal wall does not exceed 30 mm in females and 35 mm in males after opening the piriform13. The measurements made by Li et al. were 38.4 mm for males and 34.6 mm for females13, which are similar to the findings of the present study. However, Apinhasmit et al. found no statistically significant difference between males (34.77 mm) and females (33.60 mm)14. In the present study, a statistically significant difference in the anterior length was ob-
Please cite this article in press as: Oliveira GQV, et al. Cone beam computed tomography assessment of the pterygomaxillary region and palatine canal for Le Fort I osteotomy, Int J Oral Maxillofac Surg (2017), http://dx.doi.org/10.1016/j.ijom.2017.03.030
Table 2. Gender and side measurements mean and SD according to the skeletal patterns.
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served between the sexes; therefore, the osteotomy should be performed with greater caution in female patients than in male patients, because of the shorter distance that the chisel can be extended safely, without reaching the palatine canal. This difference between the sexes was also shown in the evaluation of individual sides. Thus, it is clear that these measurements should be performed preoperatively, including the individual analysis of each side, to determine the extent of the osteotomy. Variables that have not been evaluated in other studies reported in the literature are the skeletal and facial patterns. The present study demonstrated that the length of the nasal opening in the palatal canal for male individuals was statistically greater for class II subjects than for class I and III subjects. The analysis of this group showed that the length in male class II subjects was greater than that in female class II subjects (42.18 mm and 37.91 mm, respectively). In addition, male dolichocephalic subjects had a significantly greater mean length measurement than female dolichocephalic subjects. This means that there is a smaller chance of injury when performing the osteotomy of the lateral nasal wall in individuals with these anatomical features. The posterior length is the distance between the palatine canal and the pterygomaxillary fissure. It is extremely important to know this distance, because of possible injury to the palatine canal during the pterygomaxillary dysjunction if it is near the fracture line. The closer it is, the greater the chance of injury. In this study, the posterior length was found to be lower in males. Moreover, in one case, the palatine canal was located in the pterygoid process. This anatomical variation has been described by Ueki et al.12. In addition, it is important to evaluate the path and size of the palatine canal before performing the osteotomy, since the descending palatine artery is considered the main source of bleeding in Le Fort I osteotomy7,12. In this study, the palatine canal had a larger diameter for class III males; therefore such cases present a greater chance of damage to the descending palatine artery. There is discordance in the literature about whether a ligature should be performed in the descending palatine artery in Le Fort I osteotomy. Although such a ligature maintains gingival jaw perfusion22, preservation of this artery is recommended whenever possible23. Jaw impaction causes a reduced blood flow during surgery24. In class III patients, clockwise rotation of the maxilla
is commonly performed. This movement further impacts the maxilla and could therefore reduce blood flow. However, male patients have a larger palatine canal, which may compensate for this reduced blood flow. These movements usually require manipulation to remove bone interference around the palatine canal. A U-shaped osteotomy can be performed around the palatine canal to reduce the chance of injury to the descending palatine artery8. Hwang et al. evaluated the anatomical factors that could influence the pterygomaxillary separation and found that the pterygoid process had an average thickness of 7.7 mm15. In addition, the average for the group in which pterygoid fracture occurred was 4.7 mm. Thus, the subsequent thickness of the jaw was significantly greater in the group where there was dysjunction. Ueki et al. reported that the average was 1.5 mm for the right side and 1.8 mm for the left side12. However, the methodology used in the study by Hwang et al. differed from that used in the present study, since the measurement was made between the pterygomaxillary fissure and the pterygoid Plates15. Using a methodology similar to that of the present study, Dadwal et al. found that the posterior length is an important parameter for standard predicted separation in the pterygomaxillary region and was an average 4.5 mm11. When the pterygomaxillary junction is small, the stress is dissipated into the pterygoid process, unlike the cases where there is a greater thickness11. Furthermore, it is believed that in cases of small jaw thickness, there is a greater chance that the osteotome may become lodged in the nearest region or between the plates of the pterygoid process, thereby causing fracture instead of dysjunction. It has been reported previously in the literature that the greater the posterior length of the jaw, the lower the chance of fracture of the pterygoid plates, because the classic Le Fort I osteotomy technique shows a higher probability of fracture in patients with a posterior length smaller than 3.6 mm. However, measurements lower than 2.6 mm have a smaller chance of unwanted fracture of the pterygoid plates (Kanazawa et al.9). This difference may be attributed to ethnic differences in the different study samples. In the present study, the average posterior length of the jaw was 2.96 mm, indicating a greater risk of fracture of the pterygoid plates. Moreover, females had a greater posterior length of the jaw than males (3.24 mm
vs. 2.52 mm, respectively), indicating a reduced risk of fracture of the pterygoid plates in females. Regarding the skeletal pattern, class III individuals appear more likely to suffer a fracture of the pterygoid plate than class I and class II individuals (2.37 mm, 3.09 mm, and 3.23 mm, respectively). In addition, it appears that brachycephalic and mesocephalic females (posterior width 4.2 mm and 3.47 mm, respectively) are less likely to experience fracture than males with the same craniofacial patterns (2.25 mm and 2.21 mm, respectively). There is still no scientific evidence to justify the use of an osteotome to perform the osteotomy by directing it through the maxillary tuberosity28; however, this has been proposed as an alternative technique to the pterygomaxillary dysjunction5,7–11, because of the complications that may occur in this procedure. The patient’s anatomy, specifically in regard to the depth of the palatine canal, should be analyzed carefully to avoid injury and consequent haemorrhage24. Therefore, the results of this study emphasize that greater caution should be taken in performing osteotomy techniques through the maxillary tuberosity for class III female patients compared with class III male patients because of the lower depth of the descending palatine canal (Measurement D). In conclusion, knowledge of the anatomy as viewed in MSCT images is extremely important during preoperative planning for orthognathic surgery. A CT scan should be taken for all patients undergoing maxillary Le Fort osteotomy in order to visualize the artery position. Although several different surgical techniques are described in the literature, as well as a diversity of osteotomes, knowledge of the anatomical structures, such as the palatine canal and those of the pterygomaxillary region, as well as their variations according to sex, skeletal pattern, and craniofacial pattern, could reduce the risk of surgical complications. For example, the measurements of class III individuals are comparatively smaller in the pterygomaxillary region, with a greater diameter of the palatine canal, requiring Le Fort I osteotomies to be performed more cautiously. Regarding the techniques directing the osteotomy through the maxillary tuberosity, greater caution should be taken with class III female patients. Thus, a preoperative CT analysis should be performed on an individual basis and should identify the differences between the two sides in the same patient to allow a
Please cite this article in press as: Oliveira GQV, et al. Cone beam computed tomography assessment of the pterygomaxillary region and palatine canal for Le Fort I osteotomy, Int J Oral Maxillofac Surg (2017), http://dx.doi.org/10.1016/j.ijom.2017.03.030
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CBCT assessment for Le Fort I osteotomy safer surgical procedure during Le Fort I osteotomy. Funding
The authors declare that there was no funding for the present research. Competing interests
The authors declare that they have no conflicts of interest. Ethical approval
Ethical approval for the study was obtained from the Research Ethics Committee of the University of Bahia Dental School. Patient consent
Not required. References 1. Gaia BF, Pinheiro LR, Umetsubo OS, Santos Jr O, Costa FF, Cavalcanti MG. Accuracy and reliability of linear measurements using 3-dimensional computed tomographic imaging software for Le Fort I Osteotomy. Br J Oral Maxillofac Surg 2014;52:258–63. 2. Precious DS, Morrison A, Ricard D. Pterygomaxillary separation without the use of an osteotome. J Oral Maxillofac Surg 1991; 49:98–9. 3. Ueki K, Nakagawa K, Marukawa K, Yamamoto E. Le Fort I osteotomy using an ultrasonic bone curette to fracture the pterygoid plates. J Craniomaxillofac Surg 2004;32:381–6. 4. Hoffman GR, Islam S. The difficult Le Fort I osteotomy and downfracture: a review with consideration given to an atypical maxillary morphology. J Plast Reconstr Aesthet Surg 2008;61:1029–33. 5. Cheng LH, Robinson PP. Evaluation of a swan’s neck osteotome for pterygomaxillary dysjunction in the Le Fort I osteotomy. Br J Maxillofac Surg 1993;31:52–3. 6. Laster Z, Ardekian L, Rachmiel A, Peled M. Use of the ‘shark-fin’ osteotome in separation of the pterygomaxillary junction in Le Fort I osteotomy: a clinical and computerized tomography study. Int J Oral Maxillofac Surg 2002;31:100–3.
7. O’Regan B, Bharadwaj G. Prospective study of the incidence of serious posterior maxillary haemorrhage during a tuberosity osteotomy in low level Le Fort I operations. Br J Oral Maxillofac Surg 2007;45:538–42. 8. Omura S, Iwai T, Murata S, Tohnai I. Use of a simple handmade retractor to protect the descending palatine artery during removal of posterior osseous interferences for maxillary impaction in Le Fort I osteotomy. J Craniofac Surg 2013;24:978–9. 9. Kanazawa T, Kuroyanagi N, Miyachi H, Ochiai S, Kamiya N, Nagao T, Shimozato K. Factors predictive of pterygoid process fractures after pterygomaxillary separation without using an osteotome in Le Fort I osteotomy. Oral Surg Oral Med Oral Pathol Oral Radiol 2013;115:310–8. 10. Kang N, Hwang KG, Park CJ. Maxillary posterior segmentation using an oscillating saw in Le Fort I posterior or superior movement without pterygomaxillary separation. J Oral Maxillofac Surg 2014;72:2289–94. 11. Dadwal HS, Shanmugasundaram VB, Krishnakumar R. Preoperative and postoperative CT scan assessment of pterygomaxillary junction in patients undergoing Le Fort I osteotomy: comparison of pterygomaxillary dysjunction technique and Trimble technique—a pilot study. J Maxillofac Oral Surg 2015;14:713–9. 12. Ueki K, Hashiba Y, Marukawa K, Nakagawa K, Okabe K, Yamamoto E. Determining the anatomy of the descending palatine artery and pterygoid plates with computed tomography in class III patients. J Craniomaxillofac Surg 2009;37:469–73. 13. Reidel RA. The relation of maxillary structures to cranium in malocclusion and normal occlusion. Angle Orthod 1952;22:142–5. 14. Apinhasmit W, Chompoopong S, Methathrathip D, Sangvichien S, Karuwanarint S. Clinical anatomy of the posterior maxilla pertaining to Le Fort I osteotomy in Thais. Clin Anat 2005;18:323–9. 15. Hwang K, Lee DK, Chung IH, Lee SI. Le Fort I osteotomy with sparing fracture of lateral pterygoid plate. J Craniofac Surg 2001;12:48–52. 16. Herna´ndez-Alfaro F, Guijarro-Martı´nez R. ‘‘Twist technique’’ for pterygomaxillary dysjunction in minimally invasive Le Fort I osteotomy. J Oral Maxillofac Surg 2013; 71:389–92. 17. De Mol van Otterloo JJ, Tuinzing DB, Greebe RB, van der Kwast W. Intra- and
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early postoperative complications of the Le Fort I osteotomy: a retrospective study on 410 cases. J Craniomaxillofac Surg 1991;19:217–22. Tung TC, Chen YR, Bendor-Samuel RL. Surgical complications of the Le Fort I osteotomy: a retrospective review of 146 cases. Chang Keng I Hsueh 1995;18:102–7. Lanigan DT, Hey JH, West RA. Aseptic necrosis following maxillary osteotomies: report of 36 cases. J Oral Maxillofac Surg 1990;48:142–56. Ferna´ndez-Prieto A, Garcı´a-Raya P, Burguen˜o M, Mun˜oz-Caro J, Frutos R. Endovascular treatment of a pseudoaneurysm of the descending palatine artery after orthognathic surgery: technical note. Int J Oral Maxillofac Surg 2005;34:321–3. Cheung LK, Fung SC, Li T, Samman N. Posterior maxillary anatomy: implications for Le Fort I osteotomy. Int J Oral Maxillofac Surg 1998;27:346–51. Dodson TB, Bays RA, Neuenschwander MC. Maxillary perfusion during Le Fort I osteotomy after ligation of the descending palatine artery. J Oral Maxillofac Surg 1997;55:51–5. Lanigan DT. Ligation of the descending palatine artery: pro and con. J Oral Maxillofac Surg 1997;55:1502–4. Sakharia A, Muthusekar MR. A comparative assessment of maxillary perfusion between two different Le Fort I osteotomy techniques. Int J Oral Maxillofac Surg 2015; 44:343–8. Breeze J, Verea Linares C, Stockton P. Is an osteotome necessary for pterygomaxillary dysjunction or dysjunction through the tuberosity during Le Fort I osteotomy? A systematic review. Br J Oral Maxillofac Surg 2016;54:248–52. http://dx.doi.org/10.1016/ j.bjoms.2015.11.014.
Address: Division of Oral Surgery School of Dentistry Federal University of Bahia Av. Arau´jo Pinho 72 Canela 40110-912 Salvador BA Brazil Tel.: +55 71 3283 9018 E-mails: [email protected],
Please cite this article in press as: Oliveira GQV, et al. Cone beam computed tomography assessment of the pterygomaxillary region and palatine canal for Le Fort I osteotomy, Int J Oral Maxillofac Surg (2017), http://dx.doi.org/10.1016/j.ijom.2017.03.030
Int. J. Oral Maxillofac. Surg. 2017; xxx: xxx–xxx http://dx.doi.org/10.1016/j.ijom.2017.03.030, available online at http://www.sciencedirect.com
Clinical Paper Orthognathic Surgery
Cone beam computed tomography assessment of the pterygomaxillary region and palatine canal for Le Fort I osteotomy
G. Q. V.Oliveira1, M. A. Rossi2, T. V. Vasconcelos3, F. S. Neves1, I. Crusoe´-Rebello1 1 Division of Oral Radiology, School of Dentistry, Federal University of Bahia, Canela, Salvador, Bahia, Brazil; 2Department of Biomorphology, Division of Anatomy, Health Science Institute, Federal University of Bahia, Canela, Salvador, Bahia, Brazil; 3Department of Preventive Dentistry, Division of Oral Radiology, School of Dentistry, Federal University of Pernambuco, Cidade Universita´ria, Recife, Pernambuco, Brazil
G. Q. V. Oliveira, M. A. Rossi, T. V. Vasconcelos, F. S. Neves, I. Crusoe´-Rebello: Cone beam computed tomography assessment of the pterygomaxillary region and palatine canal for Le Fort I osteotomy. Int. J. Oral Maxillofac. Surg. 2017; xxx: xxx–xxx. ã 2017 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Abstract. The aim of this study was to evaluate the anatomical linear measurements of the descending palatine canal and the pterygomaxillary fissure for Le Fort I preoperative planning. Seventy-five patients, comprising 46 females (61.3%) and 29 males (39.7%), underwent multi-slice computed tomography examinations performed for preoperative orthognathic surgical planning. The images were categorized according to sex, craniofacial side, and skeletal and craniofacial patterns. The anterior length between the descending palatine canal and the lateral wall of the piriform rim showed a higher mean value for males compared to females (P = 0.0121). The posterior distance also showed a difference between the sexes and the highest mean was observed in females (P = 0.0295). Comparing the posterior width for the skeletal patterns, a statistical difference was observed between classes I and III (P = 0.0371), and classes II and III (P = 0.0094). Regarding the craniofacial patterns, the brachycephalic (P = 0.0078) and mesocephalic (P = 0.0015) groups showed a greater posterior width in females. In conclusion, the patient’s sex and aspects of the skeletal pattern and craniofacial pattern have an influence on the pterygomaxillary area and descending palatine canal anatomy. A preoperative computed tomography analysis involving this evaluation could reduce the risk of surgical complications.
Computed tomography (CT) images, along with virtual surgical preoperative planning, are important tools when performing surgical procedures. These tools potentially add new information to aid in 0901-5027/000001+07
patient management and to improve the surgical technique1. The Le Fort I osteotomy is usually indicated for the surgical correction of dentofacial deformities. Medical profes-
Key words: Le Fort I osteotomy; maxillary artery; orthognathic surgery; computed tomography. Accepted for publication 23 March 2017
sionals can carry out procedures with greater safety by better understanding the anatomy of the maxillary blood supply, and by availing themselves of today’s improved approaches and instruments.
ã 2017 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Oliveira GQV, et al. Cone beam computed tomography assessment of the pterygomaxillary region and palatine canal for Le Fort I osteotomy, Int J Oral Maxillofac Surg (2017), http://dx.doi.org/10.1016/j.ijom.2017.03.030
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However, surgical complications, such as major haemorrhage or skull fractures, may occur as a consequence of bone manipulation, mainly in connection with pterygomaxillary dysjunction2–4. Manipulation of the posterior maxilla bone following Le Fort I osteotomy may be a challenging procedure due to limited visualization, the proximity to anatomical structures such as the descending palatine artery, and the location of the pterygomaxillary region. In this regard, previous studies have reported a variety of techniques that may protect against complications and reduce the risk of injury to the patient3,5–11. In addition, some authors have highlighted that osteotomy of the medial or lateral maxillary sinus walls, pterygomaxillary dysjunction, and downfracturing of the maxilla must be performed with caution, since major bleeding from injuries to the descending palatine artery during these procedures is the most common cause of intraoperative and postoperative complications7,12. Today, osteotomies for pterygomaxillary disarticulation and the complete separation of the maxillary sinus walls are procedures that are avoided9. These approaches may increase the risk posed by surgery and the consequent susceptibility to bone fracture, haemorrhage, optic nerve damage, and arteriovenous fistula. Thus, knowledge of the anatomy in association with the appropriate surgical technique is necessary to increase the safety of Le Fort I osteotomies. Previous studies have analyzed these factors in relation to different populations, such as those of the USA13, Thailand14, and Japan12. How-
ever, there have been no reports in relation to Brazilian patients and there is also no evidence of any correlation between these aspects and the craniofacial side, patient’s sex, and craniofacial morphology and patterns. Therefore, the aim of this study was to evaluate the anatomical linear measurements of the descending palatine canal and the pterygomaxillary fissure for Le Fort I preoperative planning, as well as to assess the effects of the craniofacial side (left and right), patient’s sex, and skeletal and craniofacial patterns.
Materials and methods
The design of this study was approved by the local research ethics committee of the University of Bahia Dental School. Seventy-five adult patients, comprising 46 females (61.3%) and 29 males (39.7%), underwent multi-slice computed tomography (MSCT) examinations, which were performed preoperatively for a random group of orthognathic surgery patients. Patients presenting syndromes, cleft lip and palate, signs of maxillary tumours, facial trauma or previous surgery, and reduced maxillary sinus development were excluded from the study. The MSCT images were acquired with a 64-slice system (Light Speed VCT; GE Healthcare Bio-Sciences, Piscataway, NJ, USA), using the same settings: 120 kV, 200 mA, and 32-cm field of view, including observation of the full craniofacial complex. The axial slice thickness was 0.6 mm.
Image analysis
The right and left sides of the patient were considered separately when performing the evaluation, thus the sample comprised 150 images. These images were assessed individually under dim lighting by one previously calibrated observer using Dolphin Imaging software (version 11.7, Premium; Dolphin Imaging and Management Solutions, Chatsworth, CA, USA). The images were adjusted to ensure a parallel Frankfort horizontal (FH) plane, in order to attain a standardized head position, using the frontozygomatic sutures as a reference for the frontal view and the orbital inferior margin as well as the porion landmark for the lateral view. The orbital floors were then aligned (Fig. 1). An axial reconstruction was selected from each dataset for evaluation and the acquisition of measurements at 3 mm above the nasal floor, in accordance with a method proposed previously by Ueki et al.12 (Fig. 2). The observer established the position of the descending palatine canal in this image, and a line was drawn parallel to the most concave point of the pterygomaxillary fissure (pterygomaxillary fissure line). The following measurements were then acquired, based on the method proposed by Ueki et al.12: (1) Measurement A: anterior length (the distance between the most anterior point of the descending palatine canal and the most anterior point of the lateral wall of the piriform rim) (Fig. 3A).
Fig. 1. Three-dimensional reconstruction—frontal and lateral views of the standardized head position.
Please cite this article in press as: Oliveira GQV, et al. Cone beam computed tomography assessment of the pterygomaxillary region and palatine canal for Le Fort I osteotomy, Int J Oral Maxillofac Surg (2017), http://dx.doi.org/10.1016/j.ijom.2017.03.030
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Fig. 2. MCST reconstructions—axial reconstruction selected at 3 mm above the nasal floor.
(2) Measurement B: posterior length (the distance between the most posterior point of the descending palatine canal and the pterygomaxillary fissure line) (Fig. 3B). (3) Measurement C: width of the pterygoid plates (the narrowest width between the lateral and the medial pterygoid plates at the pterygomaxillary fissure line) (Fig. 3C). (4) Measurement D: depth of the descending palatine canal (the distance between the most lateral point of the pterygomaxillary fissure and the lateral portion of the descending palatine canal) (Fig. 3D). (5) Measurement E: diameter of the descending palatine canal (the distance
between the most anterior and the most posterior portion of the descending palatine canal) (Fig. 3E). (6) Measurement F: posterior width of the maxilla (the distance between the most posterior portion of the maxillary sinus and the most anterior point of the pterygomaxillary fossa) (Fig. 3F). (7) Measurement G: medial plate length (the shortest length between the pterygomaxillary fissure line and the most posterior point of the medial pterygoid plate) (Fig. 3G/H). (8) Measurement H: Lateral plate length (the shortest length between the pterygomaxillary fissure line and the most posterior point of the lateral pterygoid plate) (Fig. 3G/H).
The samples were divided into three groups according to the patient’s skeletal pattern assessed on a lateral cephalogram using Tweed’s classification, based on ANB measurements (the angle formed by point A, nasion, and point B) and the relationship between the jaws in sagittal view. Accordingly, 22 patients (29.3%) were classified as class I (ANB 0–4.5 ), 33 (44%) as class II (ANB >4.5 ), and 20 (26.7%) as class III (ANB <0 ). The sample was also classified into three groups based on the craniofacial pattern as described by Riedel in 1952, according to the NS–Go–Gn angle13: brachycephalic (<27 ), mesocephalic (27–37 ), and dolichocephalic (>37 ). Accordingly, 20 patients (26.7%) were
Fig. 3. Axial reconstructions and measurements: A: anterior length; B: posterior length; C: width of the pterygoid plates; D: depth of the descending palatine canal; E: diameter of the descending palatine canal; F: posterior width of the maxilla; G/H: medial plate length, lateral plate length, and pterygomaxillary fissure line.
Please cite this article in press as: Oliveira GQV, et al. Cone beam computed tomography assessment of the pterygomaxillary region and palatine canal for Le Fort I osteotomy, Int J Oral Maxillofac Surg (2017), http://dx.doi.org/10.1016/j.ijom.2017.03.030
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Table 1. General and side measurements means and standard deviation (SD) and measurements according to gender and side. Measurement
General Mean
Measurement A Measurement B Measurement C Measurement D Measurement E Measurement F Measurement G Measurement H
38.86(3.1) 2.64(1.3) 7.68(1.7) 5.07(1.6) 3.37(0.9) 2.96(1.4) 7.53(2.6) 12.17(3.2)
Side Mean Right Side
Left Side
Gender Male
Female
Right Side Male
Left Side Female
Male
Female
38.97 (3.1) 38.75(3.0) 39.79(3.2)* 38.55(2.9)* 39.88(2.9)* 38.40(3.1)* 39.70(3.4)* 38.14(2.7)* 2.70(1.2) 2.57(1.3) 2.39(1.2)* 2.85(1.3)* 2.55(1.2) 2.80(1.4) 2.28(1.3) 2.74(1.2) 7.72(1.7) 7.62 (1.8) 7.77(1.7) 7.61(1.8) 7.84(1.7) 7.65(1.8) 7.66(1.7) 7.60(1.7) 5.11(1.7) 5.01(1.6) 5.05(1.7) 5.07(1.6) 5.19(1.7) 5.06(1.7) 4.90(1.6) 5.08(1.4) 3.34(1.0) 3.40(0.9) 3.44(0.9) 3.32(0.9) 3.40(1.0) 3.30(0.9) 3.50(0.8) 3.34(0.9) 3.00(1.4) 2.92(1.5) 2.52(1.3)* 3.24(1.4)* 2.56(1.2)* 3.28(1.6)* 2.47(1.3)* 3.23(1.3)* 7.20*(2.7) 7.86*(2.4) 8.40(2.8)* 6.98(2.2)* 7.91(2.1)* 6.75(2.4)* 8.93(3.3)* 7.23(2.1)* 12.01(3.2) 12.33(3.2) 12.67(2.8)* 11.22(3.4)* 12.72(2.7) 11.55(3.3) 12.65(2.9) 12.13(3.4)
Measurement A. Anterior Length; Measurement B. Posterior Length; Measurement C. Width of the pterygoid plates; Measurement D. Depth of the descending palatine canal; Measurement E. Diameter of the descending palatine canal; Measurement F. Posterior width of the maxilla; Measurement G. Medial plate length; Measurement H. Lateral plate length. * Statistically significant (P < 0.05).
classified as dolichocephalic, 33 (44%) as mesocephalic, and 22 (29.3%) as brachycephalic. Statistical analysis
The data were analyzed using BioEstat (Mamiraua´ Institute, Bele´m, Brazil). The reproducibility was intra-observer assessed using the intra-class correlation coefficient (ICC), classified as perfect (0.81–1.0), substantial (0.61–0.80), moderate (0.41–0.60), fair (0.21–0.40), or poor (0.00–0.20). The pterygoid measurements were tested using one-way analysis of variance (ANOVA) with the post hoc Tukey test (skeletal and facial pattern) and the t-test (sex and jaw side), with the significance level set at P < 0.05. Results
The ICC values showed excellent intraobserver agreement (0.91–0.95) for all reevaluated measurements. The measurements are summarized in Table 1, according to the craniofacial side and sex. With regard to the side, a statistical difference was observed only for the medial plate length of the pterygoid process (P = 0.0072), with the left side showing a higher mean value. With regard to sex, the mean anterior length value was higher for males, with a statistically significant difference compared to females (P = 0.0121). Moreover, a statistically significant difference was also observed in males for both the right (P = 0.0397) and left (P = 0.0297) sides, compared to females. The posterior length (measurement B) also differed between the sexes (P = 0.0295), with the highest mean value observed in females. However, on analyzing the sides individually, no statistically significant differences were observed. The posterior width of the maxilla was greater in females (P = 0.0031),
and was also greater in females for the right (P = 0.0455) and the left (P = 0.0297) sides when evaluated individually (Table 1). The length of the pterygoid plates also showed difference between the sexes. In general, the measurement values were greater in males. The medial plate length differed significantly between the sexes (P = 0.0013), and also when the right (P = 0.0379) and left (P = 0.0085) sides were evaluated individually. Regarding the skeletal pattern, the anterior length (P = 0.0001) and the medial plate of the pterygoid process (P = 0.0175) were statistically larger in class II males than in class II females. In class I individuals, the lateral plate of the pterygoid process was statistically larger for males than for females (P = 0.0106). In class III individuals, the palatine canal presented a larger diameter (P = 0.0055) and depth in males (P = 0.0419). However, the posterior width of the maxilla was significantly larger in females (P = 0.0034) (Table 2). On comparing the skeletal patterns, class II and class III subjects presented a posterior width of the maxilla of 3.23 mm and 2.37 mm, respectively (P = 0.0094). Moreover, class I subjects presented a larger measurement mean than class III subjects (P = 0.0371). Considering each side individually, no statistical difference was observed between class I and class III subjects. Also, statistical difference between class I and III for medial plate length was found (P = 0.022). Regarding the class II group, the medial plate of the pterygoid process was found to be larger on the left side than on the right side (P = 0.0481) (Table 2). Regarding the craniofacial patterns, no differences were observed among the brachycephalic, mesocephalic, and dolichocephalic patterns, regardless of sex and side. However, in the brachycephalic
group, the posterior width of the maxilla was greater in females than in males (P = 0.0078), and the length of the lateral plate of the pterygoid process was greater in males (P = 0.0342). Analyzing the sides individually, the diameter of the palatine canal was significantly larger for the right side (P = 0.0206) (Table 3). The mesocephalic group presented a greater posterior width of the maxilla in females than in males (P = 0.0015). The medial plate of the pterygoid process was larger for males (P = 0.0147), and on comparing the sides, this measurement was significantly larger on the left side (P = 0.0152). The depth of the descending palatine canal in the mesocephalic group was greater for the right side (P = 0.0373) (Table 3). In dolichocephalic individuals, the anterior length was significantly greater for males (P = 0.0060), and also for the right side (P = 0.0275). Moreover, the diameter of the descending palatine canal was significantly larger on the left side (P = 0.0062) (Table 3). Discussion
It is difficult to assess some of the important structures, like the pterygomaxillary fissure and the palatine canal, during Le Fort I osteotomy. Because of the importance of these structures when performing the osteotomy, some studies have sought to correlate the anatomical parameters in the pterygomaxillary region11–13,15, with the aim of simplifying planning and surgical instrumentation in this region11. The maxillary osteotomy is considered a safe technique with a low rate of complications16, ranging from 6.1% to 9.1%17,18. Some of these complications may result from incorrect pterygomaxillary dysjunction and trauma to the structures contained in the palatine canal. It should be noted that anatomical variations
Please cite this article in press as: Oliveira GQV, et al. Cone beam computed tomography assessment of the pterygomaxillary region and palatine canal for Le Fort I osteotomy, Int J Oral Maxillofac Surg (2017), http://dx.doi.org/10.1016/j.ijom.2017.03.030
YIJOM-3654; No of Pages 7
Class
Measurements Measurement Measurement Measurement Measurement Measurement Measurement Measurement Measurement
A B C D E F G H
Class I
Class II
Class III
Class I
Class II
Class III
I
II
III
Male
Female
Male
Female
Male
Female
Right
Left
Right
Left
39.07(2.9) 2.65(1.3) 7.75(1.8) 5.12(1.8) 3.25(0.9) 3.09(1.6)¥ 7.00(2.5)* 11.80(3.2)
39.19(3.2) 2.60(1.2) 7.69(1.7) 5.07(1.5) 3.43(1.1) 3.23(1.5)* 7.37(2.3) 12.64(3.2)
38.08(2.9) 2.68(1.4) 7.55(1.8) 4.98(1.7) 3.41(0.8) 2.37(0.9)*,¥ 8.38(2.9)* 11.76(3.2)
39.47(3.2) 2.22(1.3) 7.95(1.6) 5.14(1.5) 3.29(1.1) 2.34(1.2) 7.26(2.5) 13.95(2.7)*
38.60(2.9) 2.82(1.3) 7.66(1.8) 5.15(2.1) 3.29(1.1) 3.38(1.9) 6.22(2.8) 10.97(2.7)*
42.18(2.7)* 2.50(1.0) 7.78(1.8) 4.73(1.9) 3.29(0.9) 3.49(1.5) 8.45(2.5)* 12.92(2.4)
37.91(3.3)* 2.57(1.5) 8.01(1.2) 5.17(1.1) 3.56(0.9) 3.15(1.7) 6.73(2.1)* 11.74(3.3)
38.58(2.6) 2.33(1.4) 8.00(1.8) 5.51(1.7)* 3.74(1.0)* 1.95(0.7)* 8.50(2.5) 11.44(2.8)
36.90(3.1) 3.31(1.4) 7.28 (2.0) 4.50(1.5)* 3.05(0.6)* 3.12(0.9)* 7.06(2.3) 11.43(4.2)
39.11(3.0) 2.69(1.3) 7.95(1.8) 5.33(2.0) 3.27(1.0) 2.98(1.7) 6.60(2.6) 11.79(3.0)
39.03(2.8) 2.61(1.3) 7.54(1.7) 4.92(1.5) 3.23(0.8) 3.20(1.6) 7.40(2.5) 11.86(3.4)
39.39(3.4) 2.73(1.3) 7.61(1.7) 4.96(1.5) 3.32(1.0) 3.39(1.6) 7.08(2.2)* 12.2(3.2)
38.99(3.2) 2.47(1.2) 7.78(1.7) 5.17(1.6) 3.53(1.1) 3.07(1.4) 7.66(2.4)* 13.09(3.1)
Right
Left
38.13(2.7) 2.67(1.4) 7.66(1.9) 5.11(1.7) 3.44(0.9) 2.39(0.9) 8.05(2.4) 11.93(3.3)
38.04(3.2) 2.69 (1.5) 7.45 (1.8) 4.86 (1.6) 3.37 (0.7) 2.35 (1.0) 8.72 (3.4) 11.58(3.3)
Measurement A. Anterior Length; Measurement B. Posterior Length; Measurement C. Width of the pterygoid plates; Measurement D. Depth of the descending palatine canal; Measurement E. Diameter of the descending palatine canal; Measurement F. Posterior width of the maxilla; Measurement G. Medial plate length; Measurement H. Lateral plate length. *,¥ Statistical significance (P < 0.05).
Table 3. Gender and side measurements mean and SD according to the craniofacial patterns. Craniofacial Pattern
Measurements
Brachycephalic Mesocephalic Dolicocephalic Measurement Measurement Measurement Measurement Measurement Measurement Measurement Measurement
A B C D E F G H
38.21(3.7) 3.13(0.9) 7.88(2.0) 5.17(1.8) 4.12(1.2) 3.11(1.75) 7.55(3.3) 10.9(4.2)
39.23(3.3) 2.73(1.5) 7.95(1.8) 5.44(1.7) 3.34(0.9) 3.02(1.7) 7.09(2.5) 12.31(3.0)
38.95(2.9) 2.58(1.3) 7.53(1.8) 4.84(1.7) 3.15(0.9) 2.97(1.4) 7.19(2.1) 12.04(3.0)
Brachycephalic
Mesocephalic
Dolicocephalic
Brachycephalic
Mesocephalic
Dolicocephalic
Male
Female
Male
Female
Male
Female
Right
Left
Right
Left
Right
Left
38.31(2.7) 3.13(1.2) 8.43(2.1) 5.68(1.8) 3.95(1.3) 2.25(0.5)* 7.90(3.7) 13.07(3.1)*
38.85(4.6) 3.38(1.0) 7.50(1.9) 4.92(1.9) 3.53(1.1) 4.23(1.7)* 7.78(2.8) 9.46(3.4)*
39.85(3.3) 2.30(1.2) 7.61(1.6) 5.15(0.3) 3.21(0.7) 2.21(1.0)* 8.44(2.2)* 12.91(2.7)
38.89(3.3) 2.79(1.4) 7.90(1.7) 5.43(1.6) 3.47(1.0) 3.47(0.3)* 6.70(2.5)* 11.51(3.4)
40.64(2.8)* 2.20(1.3) 7.80(1.7) 4.81(1.7) 3.50(0.9) 3.01(1.6) 8.23(3.1) 12.33(2.9)
38.28(2.4)* 2.49(1.3) 7.61(1.8) 5.07(1.5) 3.13(1.0) 2.88(1.7) 6.94(2.2) 11.60(2.9)
38.21(3.7) 3.13(0.9) 7.83(2.0) 5.17(1.8) 4.12(1.2)* 3.12(1.8) 7.55(3.2) 10.90(4.2)
38.32(3.8) 3.23(1.4) 7.87(1.9) 5.13(1.8) 3.36(0.9)* 3.14(1.4) 9.15(3.6) 11.74(2.9)
39.23(3.3) 2.73(1.5) 7.95(1.8) 5.44(1.7)* 3.34(0.9) 3.02(1.7) 7.09(2.5)* 12.31(3.0)
39.23(3.2) 2.64(1.4) 7.71(1.7) 5.01(1.5)* 3.34(0.7) 2.97(1.6) 7.71(2.5)* 12.23(3.4)
38.95(2.9)* 2.58(1.3) 7.53(1.8) 4.89(1.7) 3.15(0.9)* 2.97(1.4) 7.19(2.1) 12.04(3.0)
38.47(2.8)* 2.35(1.1) 7.49(1.7) 4.99(1.6) 3.45(1.1)* 2.84(1.2) 7.67(2.7) 12.54(3.4)
CBCT assessment for Le Fort I osteotomy
Measurement A. Anterior Length; Measurement B. Posterior Length; Measurement C. Width of the pterygoid plates; Measurement D. Depth of the descending palatine canal; Measurement E. Diameter of the descending palatine canal; Measurement F. Posterior width of the maxilla; Measurement G. Medial plate length; Measurement H. Lateral plate length. * Statistically significant (P < 0.05).
5
in this region such as an increased bone thickness or bone defects will predispose the individual to a relatively high risk of unfavourable pterygomaxillary dysjunction11. In performing an osteotomy of the lateral nasal wall, extreme caution should be taken to avoid damage to the palatine canal when separating the upper maxillary bone from the palatine bone. The descending palatine artery, contained in the palatine canal, is associated with a higher bleeding rate in Le Fort I osteotomy19. During this surgery, there is the risk of partial lesion to the descending palatine artery, evolving into aneurysm formation and bleeding in the postoperative period20. Thus, it is important to avoid the risk of this type of injury. For this reason, determining the anatomical parameters is relevant to the planning and execution of the osteotomy of the medial wall of the maxillary sinus. The present study showed that the anterior length (measurement A) was a mean 38.06 mm, with a minimum length of 30.90 mm and maximum length of 46.20 mm. Li et al. studied CT measurements and reported an average distance of 38.40 mm, ranging from 34 mm to 42 mm13. In a study on human dry skulls, Cheung et al. found a smaller average length (34.1 mm) than that found in the present study21. Their measurements also showed a wider range, with a minimum anterior length of 23.80 mm and a maximum length of 41 mm. This difference could be attributed to the greater proportion of class III individuals in the population (subjects of Asian origin). The evaluation of the individual sides revealed a mean length of 38.97 mm for the right side and of 38.75 mm for the left side, with no statistically significant difference between the sides. Ueki et al. also found no statistically significant difference between the sides and reported average values similar to those of the present study (39.1 mm for the right side and 39.4 mm for the left)12. Injuries to the descending palatine artery during Le Fort I osteotomy can be minimized when osteotomy of the lateral nasal wall does not exceed 30 mm in females and 35 mm in males after opening the piriform13. The measurements made by Li et al. were 38.4 mm for males and 34.6 mm for females13, which are similar to the findings of the present study. However, Apinhasmit et al. found no statistically significant difference between males (34.77 mm) and females (33.60 mm)14. In the present study, a statistically significant difference in the anterior length was ob-
Please cite this article in press as: Oliveira GQV, et al. Cone beam computed tomography assessment of the pterygomaxillary region and palatine canal for Le Fort I osteotomy, Int J Oral Maxillofac Surg (2017), http://dx.doi.org/10.1016/j.ijom.2017.03.030
Table 2. Gender and side measurements mean and SD according to the skeletal patterns.
YIJOM-3654; No of Pages 7
6
Oliveira et al.
served between the sexes; therefore, the osteotomy should be performed with greater caution in female patients than in male patients, because of the shorter distance that the chisel can be extended safely, without reaching the palatine canal. This difference between the sexes was also shown in the evaluation of individual sides. Thus, it is clear that these measurements should be performed preoperatively, including the individual analysis of each side, to determine the extent of the osteotomy. Variables that have not been evaluated in other studies reported in the literature are the skeletal and facial patterns. The present study demonstrated that the length of the nasal opening in the palatal canal for male individuals was statistically greater for class II subjects than for class I and III subjects. The analysis of this group showed that the length in male class II subjects was greater than that in female class II subjects (42.18 mm and 37.91 mm, respectively). In addition, male dolichocephalic subjects had a significantly greater mean length measurement than female dolichocephalic subjects. This means that there is a smaller chance of injury when performing the osteotomy of the lateral nasal wall in individuals with these anatomical features. The posterior length is the distance between the palatine canal and the pterygomaxillary fissure. It is extremely important to know this distance, because of possible injury to the palatine canal during the pterygomaxillary dysjunction if it is near the fracture line. The closer it is, the greater the chance of injury. In this study, the posterior length was found to be lower in males. Moreover, in one case, the palatine canal was located in the pterygoid process. This anatomical variation has been described by Ueki et al.12. In addition, it is important to evaluate the path and size of the palatine canal before performing the osteotomy, since the descending palatine artery is considered the main source of bleeding in Le Fort I osteotomy7,12. In this study, the palatine canal had a larger diameter for class III males; therefore such cases present a greater chance of damage to the descending palatine artery. There is discordance in the literature about whether a ligature should be performed in the descending palatine artery in Le Fort I osteotomy. Although such a ligature maintains gingival jaw perfusion22, preservation of this artery is recommended whenever possible23. Jaw impaction causes a reduced blood flow during surgery24. In class III patients, clockwise rotation of the maxilla
is commonly performed. This movement further impacts the maxilla and could therefore reduce blood flow. However, male patients have a larger palatine canal, which may compensate for this reduced blood flow. These movements usually require manipulation to remove bone interference around the palatine canal. A U-shaped osteotomy can be performed around the palatine canal to reduce the chance of injury to the descending palatine artery8. Hwang et al. evaluated the anatomical factors that could influence the pterygomaxillary separation and found that the pterygoid process had an average thickness of 7.7 mm15. In addition, the average for the group in which pterygoid fracture occurred was 4.7 mm. Thus, the subsequent thickness of the jaw was significantly greater in the group where there was dysjunction. Ueki et al. reported that the average was 1.5 mm for the right side and 1.8 mm for the left side12. However, the methodology used in the study by Hwang et al. differed from that used in the present study, since the measurement was made between the pterygomaxillary fissure and the pterygoid Plates15. Using a methodology similar to that of the present study, Dadwal et al. found that the posterior length is an important parameter for standard predicted separation in the pterygomaxillary region and was an average 4.5 mm11. When the pterygomaxillary junction is small, the stress is dissipated into the pterygoid process, unlike the cases where there is a greater thickness11. Furthermore, it is believed that in cases of small jaw thickness, there is a greater chance that the osteotome may become lodged in the nearest region or between the plates of the pterygoid process, thereby causing fracture instead of dysjunction. It has been reported previously in the literature that the greater the posterior length of the jaw, the lower the chance of fracture of the pterygoid plates, because the classic Le Fort I osteotomy technique shows a higher probability of fracture in patients with a posterior length smaller than 3.6 mm. However, measurements lower than 2.6 mm have a smaller chance of unwanted fracture of the pterygoid plates (Kanazawa et al.9). This difference may be attributed to ethnic differences in the different study samples. In the present study, the average posterior length of the jaw was 2.96 mm, indicating a greater risk of fracture of the pterygoid plates. Moreover, females had a greater posterior length of the jaw than males (3.24 mm
vs. 2.52 mm, respectively), indicating a reduced risk of fracture of the pterygoid plates in females. Regarding the skeletal pattern, class III individuals appear more likely to suffer a fracture of the pterygoid plate than class I and class II individuals (2.37 mm, 3.09 mm, and 3.23 mm, respectively). In addition, it appears that brachycephalic and mesocephalic females (posterior width 4.2 mm and 3.47 mm, respectively) are less likely to experience fracture than males with the same craniofacial patterns (2.25 mm and 2.21 mm, respectively). There is still no scientific evidence to justify the use of an osteotome to perform the osteotomy by directing it through the maxillary tuberosity28; however, this has been proposed as an alternative technique to the pterygomaxillary dysjunction5,7–11, because of the complications that may occur in this procedure. The patient’s anatomy, specifically in regard to the depth of the palatine canal, should be analyzed carefully to avoid injury and consequent haemorrhage24. Therefore, the results of this study emphasize that greater caution should be taken in performing osteotomy techniques through the maxillary tuberosity for class III female patients compared with class III male patients because of the lower depth of the descending palatine canal (Measurement D). In conclusion, knowledge of the anatomy as viewed in MSCT images is extremely important during preoperative planning for orthognathic surgery. A CT scan should be taken for all patients undergoing maxillary Le Fort osteotomy in order to visualize the artery position. Although several different surgical techniques are described in the literature, as well as a diversity of osteotomes, knowledge of the anatomical structures, such as the palatine canal and those of the pterygomaxillary region, as well as their variations according to sex, skeletal pattern, and craniofacial pattern, could reduce the risk of surgical complications. For example, the measurements of class III individuals are comparatively smaller in the pterygomaxillary region, with a greater diameter of the palatine canal, requiring Le Fort I osteotomies to be performed more cautiously. Regarding the techniques directing the osteotomy through the maxillary tuberosity, greater caution should be taken with class III female patients. Thus, a preoperative CT analysis should be performed on an individual basis and should identify the differences between the two sides in the same patient to allow a
Please cite this article in press as: Oliveira GQV, et al. Cone beam computed tomography assessment of the pterygomaxillary region and palatine canal for Le Fort I osteotomy, Int J Oral Maxillofac Surg (2017), http://dx.doi.org/10.1016/j.ijom.2017.03.030
YIJOM-3654; No of Pages 7
CBCT assessment for Le Fort I osteotomy safer surgical procedure during Le Fort I osteotomy. Funding
The authors declare that there was no funding for the present research. Competing interests
The authors declare that they have no conflicts of interest. Ethical approval
Ethical approval for the study was obtained from the Research Ethics Committee of the University of Bahia Dental School. Patient consent
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Address: Division of Oral Surgery School of Dentistry Federal University of Bahia Av. Arau´jo Pinho 72 Canela 40110-912 Salvador BA Brazil Tel.: +55 71 3283 9018 E-mails: [email protected],
Please cite this article in press as: Oliveira GQV, et al. Cone beam computed tomography assessment of the pterygomaxillary region and palatine canal for Le Fort I osteotomy, Int J Oral Maxillofac Surg (2017), http://dx.doi.org/10.1016/j.ijom.2017.03.030