DOI: https://doi.org/10.21203/rs.3.rs-1624787/v1
Purpose
Sacral slope (SS), Lumbar lordosis (LL), Pelvic tilt (PT), Pelvic incidence (PI), Sagittal vertical axis (SVA) measurements regarding anatomical structure and orientation of the lumbosacral region are very important for surgical planning and postoperative follow-up of patients. The lumbosacral transitional vertebra, which is determinant in the formation of these measurements, is effective the sacral vertebra shape and can show various anatomical variations, referred to as "sacralized L5" or "lumbarized S1".
Methods
These variations can significantly alter the sacral surface longitudinally concave on the ventral side and convexity on the dorsal side, which are observed under normal conditions. Therefore, during surgical planning in the spine, the sacrum should be determined radiologically and the vertebrae should be counted correctly. The aim of this study is to demonstrate a practical use for determining the orientation of the sacrum for sagittal balance calculation, and to recognize the sacralized L5 or lumbarized S1 segment as LSTV to avoid incorrect level surgery.
Results
Metrologically, a new index was created using the "Anterior Translational Arch (ATA1)" distance and the "Anterior Translational Angle (ATA2)" angle. 527 cases (83.3%) with anatomically normal sacrum, 35 cases (5.5%) with lumbalization and 71 cases (11.2%) with sacralization were evaluated using this index.
Conclusion
As a conclusion, the index calculated in terms of “Anterior Translational Arch (ATA1)” distance and “Anterior Translational Angle (ATA2)” provides a simple measurement to determine the transitional vertebra.
Spine-pelvic sagittal alignment has a significant impact on adults' posture and quality of life. Architecture of the lower lumbar vertebra and sacrum, pelvic orientation and lumbosacral parameters form the base of the vertebral column and play a key role in neurosurgical operations of that region [1-3]. Sacral inclination angle (SS), Lumbar lordosis (LL), Pelvic Tilt (PT), Pelvic incidence (PI) and Sagittal vertical axis (SVA) are important for surgical planning and postoperative follow-up of patients.
The anatomical structure of the sacrum is complex. The sacrum is a triangular bone formed by the fusion of five sacral vertebrae [4]. It has five different surfaces, one dorsal midline canal, four ventral sacral foramina, and four dorsal sacral foramina [5]. The ventral pelvic surface of the sacrum is concave and its dorsal surface is convex. Most of the time, the relationship of the sacrum with the lumbar vertebra can affect the anatomical structure of the lumbosacral region. Therefore, this relationship needs to be put forward correctly. The anatomical orientation of the lumbar [5] (L5) and the first sacral segment (S1) should be predominantly determined on the lumbosacral vertebra roentgenogram with the intervertebral disc and facet joints [6]. Thus, the lumbosacral transitional vertebrae (LSTV), "sacralized L5" or "lumbarized S1"can be correctly revealed.
This kind of sacralization and lumbalization in accordance with our hypothesis; It is evident that the sacral concave surface appears convex at lumbalization and therefore the anatomical orientation of that region is very important before surgery. The aim of our study is to find a practical method in deciding whether the lumbosacral transition vertebra is a sacralized L5 or lumbarized S1 segment in order to determine the S1 vertebral body, which has an important place in sagittal balance calculation, correctly and not to make incorrect measurements and to avoid erroneous and incorrect level surgery. For this purpose, the index calculated in terms of "Anterior Translational Arch (ATA1)" distance and "Anterior Translational Angle (ATA2)" was investigated to determine the transitional vertebra.
Subjects
All subjects participating in the study were pilot candidates who came to obtain a medical report to become a pilot. The lumbosacral vertebra roentgenogram studies of 633 candidates who applied to the outpatient clinic of our hospital between June 2018 and August 2018 were retrospectively analyzed. Then, anatomically normal, sacralized or lumbarized sacral vertebrae were compared using these examinations.
Imaging methods
Lumbosacral vertebra roentgenographies of all cases were evaluated. It was confirmed by the relevant radiology unit that the lumbosacral region was taken in the supine position for anteroposterior radiography and in the lateral position without flexion or extension for lateral radiography, and the position of the spine was placed in the middle of the table. It was learned that the patient was supported with radiolucent pillows from the sides to ensure that the spinal column was parallel to the table, the middle part of the detector was adjusted 6 cm above the iliac projection in the digital x-ray machine, and the procedure was performed as a standard procedure with the arms on both sides of the head and extended forward. We were informed that gonad protectors were used in male patients and the distance between the film and the x-ray tube was 100 cm. The L5 and S1 vertebrae were verified by an independent-blind radiologist with 18 years of experience in radiology.
All cases were divided into 3 groups by the radiologist. According to the criteria determined in the separated cases, the normal group (control group), sacralization group (study group 1) and lumbalization group (study group 2) were determined.
A new index (formula) was created to determine sacralization or lumbalization. For this purpose, it was investigated to create a simple formula by measuring the angles and distances between the simple lines we drew in accordance with the sacral anatomy, and whether there is a difference between sacralized and lumbarized spine.
Measurement methods
Anteroposterior and lateral radiographs of the vertebrae of all patients were obtained using standard techniques. Radiographic examination and morphometric measurements were made with the picture archiving and communication system (PACS Extreme, Ankara, Turkey). Arch and vertebral angle distance were calculated and measured on lateral radiography. Lateral projections were used as reference standards. “Anterior Translational Arch (ATA1)” as metrological measurement and “Anterior Translational Angle (ATA2)” as angle were performed.
Radiographs were initially reviewed for vertebral characterization and enumeration. The sum of cervical, thoracic, and lumbar segments above the sacrum was calculated as the total number of vertebrae. The first seven vertebrae were counted as cervical, twelve vertebrae as thoracic, and the vertebrae below the thoracic vertebra as lumbar vertebra. The first lumbar vertebra was taken as L1 vertebra. The fifth lumbar vertebra, showing the features of the adjacent sacral segment, was called sacralization. Similarly, the first sacral vertebra showing features of the adjacent lumbar segment was called lumbalization.
a) Measurement method of the ATA1
The method used for distance measurement (ATA1) is as shown in Figure 1a. The distance between the midpoint (blue line) of the line connecting the anterior aspects of the upper end of the first sacral vertebra and the lower end of the last sacral vertebra and the anterior direction of the sacral vertebral slope was called the ATA1 distance (yellow line).
b) Measurement method of the ATA 2
The method used to measure the angle (ATA2) is shown in Figure 1b. Initially, a transverse line was drawn through the upper surface of the first sacral vertebra (S1) to determine the midpoint (red line) of the anteroposterior length of S1. Next, a line was drawn (green line) connecting the midpoint of the anteroposterior length of S1 with the anterior face of the lower end of the last sacral vertebra. The angle between the blue line and the green line was named as ATA2 angle.
Statistical analysis
Statistical analysis was done by a professional statistician. In the analysis of the data, PSPP (PSPP is free software. It can redistribute and / or modify it according to the provisions of the GNU General Public License issued by the Free Software Foundation. Version 3 of the license and Microsoft Excel computer programs were used. As statistical method in the analysis of the data, descriptive analysis (mean, standard deviation, range) are given in Tables 1, 2, 3. ANOVA (Post Hoc: Bonferroni) was used to compare the three groups and to evaluate the difference between the distance and angle values between the groups. Logistic regression was used for risk analysis. Confidence interval and p <0.05 significance level Receiver Operating Characteristic (ROC) analysis test was applied to determine the cut-off point for the study groups compared to the control group for distance and angle values.
All cases consisted of young men with an average age of 18-21 years (Table 1). All of the subjects were younger than 21 years old and had no back pain, radiculopathy, or both. There was no previous history of spine surgery. There were 527 cases (83.3%) confirmed as anatomically normal sacrum. The cases with 6 lumbar vertebrae confirmed as lumbalization on anteroposterior radiography (n=35; 5.5%); in the lumbosacral roentgenogram in the lateral plane, the sacral ventral surface was convex. Cases with 6 sacral vertebrae confirmed as sacralization on anteroposterior radiography (n=71; 11.2%); in the lateral plane, the sacral ventral surface was concave on the lumbosacral roentgenogram.
The average arch distance (ATA1) of 527 patients with normal spine was 16.84 ± 6.28 mm (Fig.2a). The average arch distance of 71 cases with sacralization was 4.21 ± 5.32 mm (Fig.3a) and the average arch distance of 35 patients with lumbalization was 21.17 ± 6.68 mm (Fig.4a). The difference between the 3 groups was statistically significant (p <0.05). When we compared the groups in pairs (normal-sacralized; normal-lumbalized; sacralized-lumbalized) there were statistically significant differences (p <0.05) (Table 2).
The average angle value (ATA2) of 527 patients was 10.58° ± 1.3° (Fig.2b). The average angle value of 71 patients who underwent sacralization was found to be 8.89° ± 1.13° (Fig.3b). The average angle value of 35 cases with lumbalization was 9.86° ± 1.76° (Fig.4b). The difference between the 3 groups was statistically significant (p <0.05). When we compared the groups in pairs (normal-sacralized; normal-lumbalized; sacralized-lumbalized) there were statistically significant differences (p <0.05) (Table 3). As a result of statistical studies, it was determined that ATA1 value was more significant and sensitive than ATA2 value (Fig.5).
Spinal sagittal alignment is very important to improve the quality of life because of being a special shape of the spine and being a complex surgical method of the surgical restoration of the appropriate sagittal alignment. The basic parameters are SS, PI, LLA, inflection point, lordosis tilt angle, and global sagittal balance. The sacrum, which has a complex anatomical structure, has an important place in the calculation of these parameters. In addition, the anatomy of the sacrum is determinant in the treatment of lumbosacral orientation and spinal disorders. The ventral direction of the sacrum is concave in the vertical and horizontal planes. The first sacral vertebral body is the largest and most common area for pedicular or iliosacral screw implantation. The term lumbosacral transition vertebra (LSTV) is used for the vertebra that is "sacralized L5" or "lumbarized S1". LSTV is rare in the general population. The correlation between low back pain and LSTV was first described by Bertolotti in 1917 and was named “Bertolotti syndrome” [7]. This correlation was discussed by Elster [8]. Prevalence rates range from 4.2 to 35. In our study, we found the LSTV rate to be 16.7%.
The most commonly used method of enumerating the lumbosacral vertebrae is counting down from the T12 vertebra on lumbosacral radiographs. Moreover, if you do not have an X-ray, special attention should be paid to the presence of LSTV after MRI scanning and additional techniques are required [7]. As in most surgical errors, if operative errors are to be avoided in patients with the spinal segmental variant, LSTV, or both, the correct identification of spinal segmentation is important [9]. Lian and his friends suggest that all spine imaging and caudal count starting from C2 are the gold standard [10]. However, lumbar spine MRI is often reported without plain radiography because it is either not performed or available. There is still no consensus in the literature to define LSTV [11]. In the literature, there are different techniques reported in the literature regarding anatomical signs such as counting down from C2 or up from S5, aortic bifurcation, right renal artery, and iliolumbar ligament, but as in our study, index or scale such as ATA1 and ATA2 values was not used.
Identifying LSTV on MRI can be difficult. MRI studies in the literature have shown that the disc between an LSTV and the sacrum has a significantly reduced height compared to the normal lumbosacral intervertebral disc space [12]. Zhou and his friends have attempted to demonstrate the effect of variability in sacral endplate selection in LSVT and standardized to measure sagittal alignment in patients [13]. If LSTV is suspected, it must be decided whether it is "sacralized L5" or "lumbarized S1", because incorrect numbering of the disc will be associated with an incorrect level of operative intervention risk [14]. Besides the LL, SS, PT, SVA parameters, correction measurements and surgical planning may also change.
In the study conducted by Castellvi and his friends, LSTV was classified according to the transverse projections of the vertebrae [15]. Also, Desmond and his friends tried to classify LSTV in a different way according to disc material in T2-weighted MRI [16]. O'Driscoll and his friends determined the sacral morphology according to the presence of disc material remaining between the part thought to represent the uppermost sacral segment (S1) and the rest of the sacrum [7]. Hughes and Saifuddin suggested that both sagittal MRI study and lateral flat radiographs should be obtained prior to surgery to ensure the presence of LSTV [17]. In our study, only lateral plain radiography was preferred to confirm LSTV with suspected ventral sacral convexity. Using these images, it was found that the same measurements can be made easily with sagittal sacral MR imaging through simple calculation.
The points chosen for the new measurement method used in this study; a) The midpoint of the anteroposterior length of S1 b) the upper sacral plate, c) the angle between the line joining the anterior ends of the first and last sacral vertebra and the anterior longitudinal line of the S1-5 vertebra. These signs are easy to verify with fluoroscopy during the perioperative period. It is thought that ATA1 and ATA2 can be used in place of other measurement techniques, even in cases where it is difficult to define the C2-S5 spine lateral radiography. Although they reported that the angle measurement technique they found in a study by Farshad and his friends was effective in determining the transitional vertebra, the anterior arch distance we found in our study was also a sensitive method [18]. As can be understood from the measurements we made, when the transition arc distance is less than 10 mm sacralization should be considered. When sacralization is greater than 21 mm, lumbalization should be considered. However, this method may be inadequate in obese patients due to the inadequacy of plain radiological imaging. This is a problem that can be overcome with MRI. Larger and more practical clinical studies are also needed to evaluate the effectiveness and practicality of the method.
As a result, if LSTV due to ventral sacral convexity is suspected, preoperative lateral plain radiography can provide a simple measurement to detect the transitional vertebra. In addition, ATA1 measurement is a sensitive method that can identify an LSTV on lateral radiography or single slice mid-sagittal MRI.
LSTV: Lumbosacral Transitional Vertebra
ATA1: Anterior Translational Arch
ATA2: Anterior Translational Angle
SS: Sacral inclination angle
LL: Lumbar lordosis
PT: Pelvic Tilt
PI: Pelvic incidence
SVA: Sagittal vertical axis
Ethical Approval
Ethics committee application of our article; It was approved by the Clinical Research Ethics Committee of the Turkish Republic Health Sciences University, Diskapi Yildirim Beyazit Training and Research Hospital, with the decision number 106/07, dated 08.03.2021.Availability of data and materials
Availability of data and materials
The datasets analyzed during the current study are available from the corresponding author on reasonable request.
Author Contributions
Cem ATABEY ; writing, checking, data collection, editing
Ahmet GUNAYDIN; data control, table preparation
Ahmet EROGLU; typing, figure control
Meltem OZDEMIR; figure preparation, control
Ahmet Metin SANLI; figure control, editing