MORPHOMETRY OF THE POSITIONING OF CORTICAL TRAJECTORY PEDICLE SCREWS IN BRAZILIANS

Objective: Morphometric study of the positioning of the cortical trajectory pedicle screw in the lumbar spine of Brazilian patients of different sexes and ages, through the use of computed tomography images, in order to obtain more reliable data about cortical screw insertion and the variations observed, providing assistance for a safer, more effective approach with fewer complications. Methods: Selection of 100 patients from a database, alternating by sex, measuring the length, diameter, cephalic angulation, and lateral angulation of the vertebrae from L1 to L5. Results: Statistically significant measurements were obtained for the four different parameters in relation to sex. The mean age was 56, with a minimum of 20 and a maximum of 87 years. The L4 and L5 screws showed a reduction in relation to the other levels, while the width showed a progressive increase starting at L3. Lateral angulation was the parameter with the least variation among the levels, while there was greater variation and a reduction from L4 to L5 in cephalic angulation. Conclusion: Statistically significant results were obtained for length, diameter, lateral and cephalic angulation. Sex was a significant factor in spine surgery instrumentation using the cortical trajectory pedicle screw technique. Level of evidence I; Diagnostic study (investigation of an examination for diagnosis). datos, con alternancia de sexo, midiendo la longitud, diámetro, angulación cefálica y angulación lateral de las vértebras desde L1 hacia L5. Resultados: Fueron obtenidas medidas con significancia estadística con relación al sexo en los cuatro diferentes parámetros medidos. El promedio de edad fue de 56 años, con edad mínima de 20 y máxima de 87 años. Los tornillos de L4 y L5 mostraron reducción con relación a los otros niveles, mientras que el ancho se mostró progresivo a partir de L3. La angulación lateral fue el parámetro que presentó la menor variancia entre ellos, al contrario de la angulación cefálica, con mayor variación y disminución de L4 y L5. Conclusiones: Fueron obtenidos parámetros de longitud, ancho, angulación lateral y cefálica estadísticamente significativos. El sexo se presentó como factor en la instrumentación de la cirugía de la columna por la técnica del tornillo pedicular de trayecto cortical . Nivel de evidencia I; Estudio Diagnóstico (investigación de un examen para diagnóstico). Descriptores: Tornillos Óseos; Fusión Vertebral; Columna Vertebral/cirugía.


INTRODUCTION
For several decades, fixation with pedicle screws has been the main technique used for stabilization of the lumbar spine in the treatment of lumbar spinal conditions such as fractures, tumors, and degenerative disease. 1 The insertion of pedicle screws into the lumbar spine is performed through the pedicle, from the lateral to the medial, the point of insertion being located at the junction of the transverse process of the lumbar vertebra with the lateral wall of the upper facet of the vertebra to be fixed. 2 Several potential complications are associated with this technique, such as dislocation of the screw and loss of stability, especially in patients with osteopenia or osteoporosis. 3 Another disadvantage includes the significant muscle dissection necessary for the insertion of pedicle screws due to their lateral to medial trajectory 3 and the risk of neural tissue injury. 3,4 In the last decade, several advances have been achieved in the development of new screws and new insertion techniques, all seeking to optimize the biomechanical properties and/or minimize the risk of complications. 5 Santoni et al. 6 were the first to describe the cortical trajectory lumbar pedicle screw, known simply as the "cortical screw." The cortical trajectory pedicle screw has its own placement, different from the classic pedicle screw. It has a caudal to cephalic path in the sagittal plane and medial to lateral path in the horizontal plane. Its idealization came from the challenge of performing instrumentation in patients with bone fragility resulting from osteoporotic disease. The objective was to create a screw path with greater contact with the cortical bone and, therefore, greater resistance to pullout.
Since then, numerous studies on this new technique have been conducted, demonstrating its characteristics and its potential benefits, comparing it directly with the classic pedicular technique.
This technique has been shown to be safe even for use in pediatric surgeries. 7 Biomechanical studies have shown the advantages of this technique, including insertional torque superior to the traditional and lower incidence of overall complications. 2,8,9 As regards functional improvement and pain, it is similar to the traditional technique in preliminary studies. 9,10 Cortical trajectory pedicle screw fixation can vary depending on factors, such as cephalic angulation and the size of the screw inside the lamina, as well as individual patient factors, such as bone density. Extensive anatomical knowledge is important for the placement of the lumbar fixation screw, since it can potentially offer better outcomes and fewer complications. Consequently, understanding the morphometric variability in the Brazilian population can enable a safer and more effective approach.
The objective of this study was to measure the morphometric placement parameters of pedicle screws inserted in the lumbar spines of Brazilian patients of different sexes and ages, in order to obtain more reliable data about cortical screw insertion and the variations observed, thus providing assistance for a safer and more effective approach with fewer complications.

METHODS
This was a retrospective study, submitted to and approved by the Institutional Review Board of the Hospital Mater Dei (identification number 04315318.0.0000.5128), in which we evaluated medical records and reviewed tomographic images. The participants of this study signed the Informed Consent Form.
We evaluated 100 computed tomography scans of the lumbar spine performed at the same institution: Rede Mater Dei de Saúde, Belo Horizonte, Minas Gerais. CT scans performed between 02/23/2018 and 11/21/2018 were included in the database for medical record review, 50 of which were of female patients and 50 of male patients. The exclusion criteria were fractured pedicles and pedicles with congenital alterations and other deformities.
The following measurements were taken: maximum length, maximum width in the axial plane, lateral angle in relation to the axial plane, and cephalic angle in relation to the sagittal plane. Alternately, the right or the left pedicles of the same lumbar spine were measured. All measurements were taken by the same radiology specialist in order to reduce the measurement bias and were based on the illustrations in Figures 1 and 2. The parameters described by Matsukawa et al. 11 were used, with the point of insertion of the screw being the intersection of a line drawn in the median of the upper articular process of the vertebra and another perpendicular line located one millimeter caudal to the lower edge of the transverse process, as illustrated by the point in Figure 1.
The measurement data obtained were compiled in an Excel software table. For the statistical calculations, an exploratory analysis was first performed in order to determine the normality of the data. Quantitative variables were submitted to the D'Agostino-Pearson and Shapiro-Wilk normality tests. Following the normality tests, the median, the 25th and 75th percentiles (P25 and P75), and the minimum and maximum values of each of the variables were calculated.
An assessment of possible statistical differences between the different levels (L1 to L5) was conducted using the Kruskal-Wallis test, followed by Dunn's test of multiple comparisons. The Mann-Whitney test was used for the comparison of the measurements within each level in relation to the sex of the patient.
The research data were processed in the GraphpadPrism ® version 5.0 for Windows statistical program and in all statistical tests a level of significance of 5% was considered. Thus, associations with a p value less than 0.05 are statistically significant.
The measurements of pedicles with any kind of malformation, fractured vertebrae, or tumors were excluded from the calculations.

RESULTS
The median age of the patients in this study (n = 100) was 56 years, with a minimum of 20 and a maximum of 87 years of age. The median age was similar between the sexes (p = 0.8496), with the median age of the female patients being 56 years (minimum of 20 and maximum of 87 years) and the median age of the male patients was 57 years (minimum of 25 and maximum of 86 years), as shown in Figure 3.
The median maximum bone lengths (L1 to L5) of the total number of patients (n = 100) are shown in Figure 4. The data obtained showed that there was no statistical variation between the median bone lengths of levels L1 to L3. However, there was a significant reduction in the L4 and L5 measurements (p < 0.0001) ( Figure  4A). The measurements taken at level L4 of the lumbar spine were statistically lower than the measurements of levels L1, L2, and L3 (p < 0.0001). Level L5 had the lowest median bone length value as compared to the other levels (p < 0.0001). In relation to sex, both female and male patients presented this significant reduction in the bone length of levels L4 and L5 of the lumbar spine. In female patients, L4 measurements were only lower than those of L2, while L5 was statistically lower than all the other levels (p < 0.0001) ( Figure  4B). Male patients presented the same statistical behavior as the total population: L4 < L1-L3 and L5 < L1-L4 (p < 0.0001) ( Figure 4C). The maximum bone diameter of the total number of patients from levels L1 to L5 had the following median values: L1 = 6.46 (min. 3.64 -max. 12.26), L2 = 6.64 (min. 4.51 -max. 12.35), L3 = 7.92 (min. 5.28 -max. 13.26), L4 = 10.08 (min. 5.55 -max. 14.39), and L5 = 13.72 (min. 1.86 -max. 21.62) ( Figure 5A). The median bone diameter was smaller at levels L1 and L2 and increased gradually to level L5. There was a significant difference between all the pairs (p < 0.0001), except L1 versus L2 (p > 0.05). As regards sex, both female and male patients showed this significant increase in bone diameter. In female patients, the same statistical behavior as in the total population was observed. In the male patients, in addition to the L1 versus L2 pair, the L1 versus L3 pair also showed no statistically significant difference (p > 0.05) ( Figures 5B and 5C).
The  Figure 6A). When grouped by sex, this absence of significant difference was maintained among the female patients (p > 0.05), while there was a gradual significant increase observed among the males (p = 0.0165) when we compare the groups simultaneously. However, Dunn's test was not able to identify the specific pair related to the significant difference. (Figures 6B and 6C) The median cephalic angulation values for all the total number of patients at levels L1 to L5 were as follows: L1 = 25.02 (min.  Figure 7A). The data obtained showed no statistical variation in cephalic angulation between levels L1 to L3. However, there was a significant decrease in these measurements at levels L4 and L5 as compared to the higher levels (p < 0.0001), though this decrease was similar in both (L4 = L5, statistically). When analyzing by sex, among the females we observed a decrease in cephalic angulation at levels L4 and L5 only in relation to L1, and at level L5 also in relation to L2 (p < 0.05). Among the males, L4 presented a significant decrease when compared to the lower levels (p < 0.05) and was similar to L5, which, in turn presented a significant decrease only in relation to L1 and L3 (p < 0.05). (Figures 7B and 7C) In the comparison of the measurements between the sexes, we observed statistical differences between the bone lengths at levels L1 to L5 between male and female patients (p < 0.05) ( Table 1). At level L1, median bone length was statistically greater in male patients than that observed in female patients (37.67 mm versus 35.94 mm, respectively) (p = 0.0310). At level L5, median bone length was statistically greater in female patients (27.97 mm) than in male patients (26.02 mm) (p = 0.0333). The other levels did not present any significant changes in the comparison between the sexes (p > 0.05).
In turn, there were statistical differences between female and male patients in bone diameters of levels L1, L2, L3, and L4 (p < 0.05). At levels L1 and L4 the median bone diameter of male patients was statistically greater than that observed in female patients (p ≤ 0.0001). There was no significant difference at level L5 between the median bone diameter of female patients (13.75 mm) and that of male patients (13.59 mm) (p > 0.05). (Table 1) In the comparison of the relationship between lateral angulation and the sagittal axis at each level, there were statistical differences at all levels for both female and male patients (p < 0.0001)    (Table 1). In the comparison of the relationship between cephalic angulation and the horizontal axis at each level, the measurements of levels L1, L2, L3, and L4 were higher for females than for males (p < 0.05) ( Table 1).

DISCUSSION
The pedicle screw is currently the main method of choice for instrumentation in spinal surgeries, being considered the gold standard.
Since it was described by Santoni et al., 6 several studies have been conducted supporting the use of cortical screws as a safe and biomechanically suitable alternative method for lumbar spine fixation. It is a less invasive technique of special biomechanical importance in osteoporotic bones.
If this study, we took morphometric measurements with the goal of observing the most reliable parameters for screw placement in the Brazilian population, taking sex into account in a sample with a broad age range. Recently Matsukawa et al. 11 studied morphometric parameters through a review of 100 tomographies of predominantly male patients and with a mean age of 37 years. In our study, our random choice of patients of both sexes for inclusion in the calculations was aimed at complementing the limitation (single sex and little variation in age due to the military environment where the experiment was conducted) referred to by Matsukawa et al. 11 in their conclusion.
Correct cortical screw placement through more targeted parameters helps to prevent complications. This study argues that there are four critical parameters that contribute to lumbar spine instrumentation.
Zhang et al. 10 proposed a new point of screw insertion, using the lower instead of the upper facet as the bone reference. Unlike that used by Matsukawa et al. 11 and the present study, Zhang et al. 10 aimed for less destruction of the soft parts, attempting to keep the joint capsules whole. More recent parameters were again used by Senoglu et al. 12 and Gao et al., 13 both maintaining the point of insertion of Matsukawa et al. 11 The length measurement results obtained for pedicles L1 to L3 were similar to those of Matsukawa et al., 11 both in terms of the median values and the pattern of the ascending curve. The same, however, was not observed in relation to L4 and L5. Despite the similarities between the two studies, both with the curves descending from L4 to L5, the values obtained from our measurements were lower. Zhang et al. 10 observed a similar pattern of growth from L1 to L3 and an L5 length less than that of L4, but with lower values. Even though points of insertion were different, the outcomes of this study validated the results found by Zhang et al. 10 and by Matsukawa et al. 11 Senoglu et al. 12 reported that in previous studies the lengths  Although not addressed in our study, Matsukawa et al. 11 established cortical screw parameters for S1 insertion, with insertion at the junction of the center of the upper facet joint of S1 and a point approximately 3 mm below the lowest point of the L5 facet joint. Two years later, this information was contrasted by Zhang et al., 10 who established the point of insertion as the junction of the medial border of the S1 pedicle and the lower border of the lower facet joint of L5, reporting that it is closer to the upper plateau and therefore easier to see.
The differences in diameter observed corroborate the findings of Matsukawa et al., 11 who reported differences in the same pairs of measurements as well as a gradual increase.
The lateral angulation results from the analysis of the tomographies of the total group corroborated the findings of Matsukawa et al. 11 We observed a significant decrease in the cephalic angulation of L4 and L5 in relation to the other levels, which contradicts the findings of Matsukawa et al., 11 who did not find any significant differences in the cephalic angulation in relation to the horizontal axis. The decrease would imply alterations in the positioning of the instrumentation in an attempt to prevent injury to the upper plateau.
The random choice of patients of both sexes to be submitted to the calculation was intended to exclude the limitation referred to by Matsukawa et al. 11 in their conclusion, as their measurements were taken predominantly from male subjects with a mean age of 37 years (selection inside a military environment). Comparisons by sex with statistical significance were observed.
When we analyzed the differences between the sexes, we observed that in several measurements the male patients had values higher than those of the females, with the exception of vertebra L5, where the female patients presented greater length and cephalic angulation, statistically significant when compared to L1 and L4. Level L5 presented the smallest difference between the sexes, where we observed statistical differences in the length and lateral angulation measurements. Such observations add information that assist the surgeon in the instrumentation of patients of both sexes.
Positive results were reported for the treatment of patients with spondylolisthesis using hybrid construction with proximal cortical screws and the conventional method at the caudal level. 14 Zhang et al. 10 cited the possible advantage of using it in obese patients due to the need for less dissection in these patients.
In a review conducted by Phan et al, 15 the literature was still not completely cohesive in terms of results and complications when comparing the traditional pedicular screw approach with the cortical approach, which emphasizes the importance of conducting more studies addressing the cortical approach.

CONCLUSION
The parameters obtained in this study, still not documented for the Brazilian population, add information and serve as an aid to the surgeon in the instrumentation of patients of both sexes. The data obtained are based on statistical studies and the median values act as a suggestion for surgery, which must respect the steps of individual analysis and the variations in each patient during instrumentation.
This study is an attempt to improve spinal instrumentation techniques. As such, it used concrete data resulting from a scientific experiment that followed all the norms of academic research as a reference. However, a consensus still must be established around the best clinical and radiographical parameters for fabrication of the cortical screw so that the technique may become more applicable.
All authors declare no potential conflict of interest related to this article.