Le Fort I osteotomy is a procedure frequently applied in orthognathic surgery to correct a wide range of malocclusion and maxillofacial deformities.
Complications in Le Fort I osteotomy can occur from dysjunction of the pterygoid plates from the posterior maxillary wall and the fissure is the triangular -shaped lateral opening of the pterygopalatine fossa formed by the divergence of the maxilla from pterygoid process of the sphenoid bone [29, 30]. The complications seemed to occur because of the close relation of the fissure to the pterygopalatine fossa, foramina of the base of the skull, and orbit [11, 13, 31–33]. The most common are intraoperative and postoperative hemorrhage secondary to damage to the maxillary artery and its terminal branches (descending palatine and sphenopalatine arteries), followed by varying degrees of maxillary ischaemic necrosis [35–37].
Furthermore, the anatomical structure of the sphenoid sinus is important when surgeons access to the pterygomaxillary region connected to the anterior region of the base of the skull. In-depth knowledge of this region has become essential to predict what may be found, so that possible anatomical variations can be accounted for, and iatrogenic lesions such as damage to the internal carotid artery and other important structures, can be avoided [38].
Sphenoid sinus traumas or inflammations can cause severe complications that are potentially fatal and visual changes that have been common ranging from 12–70% of isolated sphenoid diseases [39]. During the separation of the pterygomaxillary junction, due to the inappropriate forces to the base of the skull via the sphenoid bone and incorrect instrumentation, particularly when nasal septum osteotome is placed too high into the nasal cavity, sphenoid sinus and various adjacent vital structures may be damaged and serious bleeding, neurological complications or blindness, or even death may arise from the operation area [1, 4, 31]. Unwanted fractures extending the cranium could cause cavernous sinus thrombosis or carotid-cavernous sinus fistula; by this way, permanent cranial nerve damage could be observed [31, 32]. These neurological injuries could be isolated or combined and are related to direct or indirect injury [32]. Bony segments resulting from unexpected and unwanted fractures during down fracture of maxilla or with nasal septum or pterygoid osteotome may damage this region. On the other hand, various reasons such ischemia or contusion of a nutrient artery may cause indirect injuries of the adjacent cranial nerves [31, 32]. It is described that direct trauma to the medial aspect of the cavernous sinus bypassing sphenoid sinus may cause neurological complications [40].
Moreover, east-Asian patients generally have a brachycephalic facial type, low projection of the nose, shorter anterior cranial base, and protrusive maxilla [16, 41–43]. Posterior repositioning of the maxilla is necessary for an optimum aesthetic profile in Asians, although the technique has several difficulties and complications. Ueki et al. first proposed the concept of the intentional pterygoid plate fracture with an ultrasonic bone curette [16]. After then some surgeons have reported the clinical evaluation including stability or healing pattern of the intentional pterygoid plate fracture with and without use of the ultrasonic bone curette [16–21]. The previous anatomical studies have showed that the distance from the internal maxillary artery to the inferior point of the pterygoid plate is approximately 23–28 mm [44, 45]. Based on the quantitative measurements of the fracture line, whether the fracture level was high or low, the most superior point of the fracture line was always far lower than the position of the internal maxillary artery [21]. However, in our experiences, the sphenoid sinus perforation occurred, although there was no internal maxillary injury and no symptom occur after surgery fortunately.
Furthermore, ethnicity, sex, and age are all factors that have an influence, and it has also been suggested that nasal airflow and positive air pressure in the nasopharynx affect the development of the paranasal sinuses and craniofacial growth [46]. According to some authors the development of the paranasal sinuses is linked directly to the growth of the facial part of the skull and with dentition [47, 48]. In the previous study without description regarding skeletal class,46 it was found that both maxillary and frontal sinus volumes were greater in males compared to females, but there was no statistically significant correlation between the volume of maxillary sinuses with age or side. It was reported that sex, facial type, and skeletal class had no significant influence on the volume of the sphenoid sinus, and nor did the volumes of the right and left sphenoid sinuses, or the presence of a septum within the sinus in its volume [49].
In this study, there was no correlation between sphenoid sinus and age and this finding was in accordance with the previous studies [46 49]. However, there were significant differences between class III male and class III female in HS, VDS and WS. Although there was significant difference between class II and class III in ML, this measurement showed antero-posterior length of maxillary sinus and might not reflect the sphenoid sinus.
The previous studies reported that the mean distance from the piriform fossa to the descending palatine canal was 38.4 mm in men and 34.6 mm in female [30], and 34.1 mm using CT of dry skull [50]. They stated that injury to the descending palatine artery during the Le Fort I osteotomy can be minimized by not extending the osteotomy more than 30 mm posterior to the piriform rim in females. In this study, the mean anterior length was 30.4 mm in class II female and 27.90mm in class III female on right side, both shorter than other studies. This may be due to the difference in the measurement points, as we selected the distance between anterior wall and posterior wall of the maxillary sinus at the PNS level plane parallel to the FH plane on the side-sagittal plane involving the great palatine canal.
Furthermore, the differences in all measurements between the right and left sides did not correlate with asymmetric measurements, such as the Mx-Md midline. This suggested that the right-left difference in maxilla-mandibular asymmetry did not relate to the right left difference morphology of the sphenoid sinus and pterygomaxillary region.
This study was described to help the surgeons to access the sphenoid and the pterygomaxillary region when the Le Fort I osteotomy and removal of the bony interference with and without the intentional pterygoid fracture. Therefore. the anatomy of the anterior wall of sphenoid sinus and the posterior wall of maxillary sinus and great palatine canal was emphasized in the measurements. Especially, VDS represented the vertical distance from the PNS level to the sphenoid sinus wall. In short, after down fracture of maxilla, the knowledge of the distance was useful to perform the horizonal osteotomy at the frontal aspect of the pterygoid plate. The fracture level of the pterygoid plate can be determined referring the maxillary structure. In this study, the mean VDS was ranged from 18 to 20 mm, however the standard deviation of VDS was comparatively large (4–6 mm). The vertical distance to the sphenoid sinus is so varied that use of the pterygoid osteotome and the curved lateral nasal wall osteotome can damage the upper level of the pterygoid plate including sphenoid sinus, even if the intentional pterygoid plate fracture is not performed. When maxillary impaction at the posterior site and/or maxillary setback are performed, surgeon is forced to operate at the upper level of the pterygomaxillary region close to sphenoid sinus. The internal maxillary artery, descending palatine artery, sphenopalatine artery, superior palatine artery, the pterygoid venous plexus and the pterygoid muscles exist at the upper level of pterygopalatine fossa between the pterygoid plate including the sphenoid sinus and posterior wall of maxilla. From the results if stepwise regression analysis, Ramus inclination (right and left) and Occlusal plane to FH (Right) in cephalometric measurements were selected as variables related to the VDS. This suggested that the cephalometric analysis could be helpful to determine the horizontal fracture level of pterygoid plate. Although there was significant difference, the prediction using only the cephalometric measurements might not be accurate and realistic to determine the horizonal osteotomy at the frontal aspect of the pterygoid plate, clinically.
As a limitation of this study, the normal skeletal with normal occlusion control and class II male subjects were not prepared. Therefore, it was still unclear whether there were differences among all skeletal patterns including class II in male. Furthermore, larger sample number will be necessary to evaluate more objectively.
Anyway, surgeons must pay attention not only the bleeding from the vessels and the muscles but also the sphenoid bone damage including pterygoid plate and sphenoid sinus that sequentially can induce the fatal cerebral or nerve damage.