Computed Tomography-Based Morphometric Analysis of the Thoracolumbar Junction in the Young Turkish Population

Introduction

Fractures of the thoracolumbar junction (TLJ) represent 90% of all spine fractures [1]. This area comprises T11 to L2 vertebrae and is biomechanically the spine’s weakest point [1,2]. The transition from the less mobile thoracic spine with its associated ribs and sternum to the more dynamic lumbar spine makes this an area of great biomechanical stress [3]. Appropriate treatment for TLJ injuries is critical [4]. Current treatment goals include preventing neurologic damage, achieving adequate stability and fusion, restoring sagittal balance, initiating early rehabilitation, and returning the patient to work. However, much debate remains about what represents the ideal treatment [4].

Scoliosis is a spinal deformity characterized by lateral curvature and rotational deformity of the vertebrae. The causes of scoliosis are varied and can be broadly classified into congenital, neuromuscular, syndrome-related, idiopathic, and secondary spinal curvatures. The natural progression of scoliosis is influenced by its underlying etiology and the age at which it presents, factors that typically guide treatment decisions. However, a thorough evaluation of scoliosis relies on the patient’s medical history, physical examination, and radiographic findings, which are essential in identifying cases requiring further investigation. The management of idiopathic scoliosis is determined by the patient’s age, curve severity, and risk of progression, with treatment options including observation, orthotic management, and, in some cases, surgical correction through spinal fusion [5].

Kyphotic deformity that develops after the injury is critical in determining the treatment of vertebral fractures by showing the stability of the injured segment [6,7]. Numerous studies have characterized the physiological sagittal alignment of the spine at the TLJ [8–11]. However, the results obtained were either small-scale or included patients of different races; this makes it difficult to use them as reference values. Consequently, the aim of this study was to examine the normal sagittal alignment of the TLJ and adult degenerative scoliosis in a young adult Turkish population. We planned such a study to create a database based on computed tomography (CT) of the morphometric characteristics of the vertebrae of the TLJ (T11-L2) for both sexes in the Turkish population and to use these findings in the diagnosis of injuries to this region and in treatment planning. We hypothesized that the normal sagittal Cobb angles we obtained would be beneficial to clinicians in the treatment of TLJ injuries. Therefore, this CT-based morphometric study aimed to evaluate the segmental Cobb angles of T11, T12, L1, and L2 vertebrae in 1500 healthy individuals between 20 and 39 years of age.

Material and Methods

ETHICAL CONSIDERATIONS:

This study was conducted in accordance with the ethical principles stated in the Declaration of Helsinki and was approved by our institutional ethics committee (date of approval: July 07, 2022, protocol no: 219). Due to the retrospective nature of the study and the minimal risk to patients, there is no requirement for informed consent.

STUDY POPULATION:

Patients between the ages of 20 and 39 years who applied between 2018 and 2021 and had thoracic vertebrae, lumbar vertebrae, thorax, and upper abdomen CT were examined for the study. The CT scans evaluated for the study were selected from patients who applied to the hospital with TLJ concerns, including abdominal pain and kidney stones. The CT scans taken between 2018 and 2021 were examined, and the files of the patients who had imaging between the T10 and L3 vertebrae were examined. Patients with normal neurological examinations, patients without pathologies related to the vertebral column, and patients who had not previously undergone surgical treatment related to the vertebral column were included in the study. The CT scans were reviewed, and individuals with spinal pathologies or a history of surgery were excluded from the study. In the controls made from the patients’ files, those with a body mass index below 18.5 and above 30 were excluded from the study. During CT scans, patients were in the supine position with their arms at their sides and without any pillows under their legs. All CT images (1.0-mm slice thicknesses, 150 kVp) were obtained with the SOMATOM Force CT scanner (Siemens Healthcare, Erlangen, Germany).

RADIOLOGICAL MEASUREMENT METHODS:

Using Cobb angles is a standard method for determining spinal curvature [12]. While performing morphometric analysis, measurements were made from sagittal sections of CT scans where the spinous process was fully visible. The Cobb angle was defined as the angle between the upper end plate of the vertebra above and the lower end plate of the vertebra below the vertebra of interest [13]. For instance, to measure the global Cobb angle from T11 to L2, the angle between a line drawn from the superior end plate of T10 and the inferior end plate of L3 was evaluated. In the case of segmental Cobb angles, the upper end plate of the upper vertebra and the lower end plate of the lower vertebra of the segment to be measured were used (Figure 1). The superior end plate was described as the line connecting the most anterosuperior and posterosuperior corners of the vertebral body, while the inferior end plate was defined as the line between the most anteroinferior and posteroinferior corners [14]. Radiological measurements were executed using the Extreme XDS Picture Archiving and Communications Systems version 4.3 software available at our institution. All measurements were performed twice, independently by 2 senior trauma surgeons. The segmental Cobb angles at T11, T12, L1, and L2, as well as the global Cobb angle from T11 to L2, were measured for the TLJ. Positive values of the Cobb angle represented kyphosis, while negative values indicated lordosis.

STATISTICAL ANALYSIS:

All statistical analyses were conducted using SPSS 25.0 software (IBM Corp, Armonk, NY, USA). The Shapiro-Wilk test and Kolmogorov-Smirnov method were used to investigate normally distributed data. For comparisons of continuous data (mean values), the mean, standard deviation (SD), mean difference, 95% confidence interval (CI), and P value were reported. The intraclass correlation coefficient (ICC) with a 95% CI was used to evaluate intraobserver and interobserver reliability. The t test was used to compare segmental and global Cobb angles between the 2 groups, which were categorized by sex. P<0.05 was considered statistically significant.

Results

GENERAL CHARACTERISTICS OF PATIENTS:

The mean age of the 1500 patients included in the study was 29.5±5.7 years. The average height of the patients included in the study was 164.6±4.5 cm for women and 176.3±5.1 cm for men. The average weight of women was 57.3±5.2 kg, and 74.3±7.8 kg for men. Demographic data of those included in the study are summarized in Table 1.

RESULTS OF COBB MEASUREMENTS:

As a result of the measurements, the average of the angles measured at the T11 and T12 levels was 6.5° kyphotic. The average angle at the L1 level was 2.7°±4.8° kyphotic. The average at the L2 level was −2.5°±5.7° lordotic. The average of the global angles between T11 and L2 was 3.9°±6.5°. The mean values of segmental and global Cobb angles measured in the study by sex are shown in Table 2. The Cobb angles measured in the study were grouped according to sex as the 20s and 30s, and the data obtained are shown in Table 3.

INTRA- AND INTEROBSERVER AGREEMENT:

The ICC value of the measurements made by observer 1 was 0.913, and the agreement was evaluated as excellent. The ICC value of the measurements made by observer 2 was 0.924, and the agreement was evaluated as excellent. Interobserver agreement was also found to be excellent (ICC: 0.918).

Discussion

The present study demonstrates that, although global morphometric parameters of the TLJ did not exhibit significant sex-based differences within the young adult cohort, age-stratified analyses revealed statistically significant variations at the segmental level. These findings imply that sagittal alignment characteristics of individual TLJ segments can be influenced by chronological aging and sex-related anatomical differences.

Surgical planning is very important before spine surgeries. While doing this planning, radiological images can be made manually and using deep learning frameworks [15]. Determining the length and diameter of the screws to be applied, ensuring balance in the sagittal plane, and minimizing postoperative complications should not be ignored. Güleç et al [16] reported morphometric analysis of the spines in the lumbar region in the Turkish population. However, unlike our study, they did not perform sagittal plane analysis in their study.

Kwon et al [6] reported the sagittal Cobb angles of TLJ in a young Korean population of 1000 individuals. They found the global sagittal Cobb angle of TLJ to be 0.5°. However, our study revealed this value to be approximately 4° of kyphosis. These findings suggest that different ethnic groups can exhibit varying values.

Wood et al [17] reported the TLJ sagittal Cobb angle of 50 asymptomatic individuals as 5.1° in their study in the United States. Viella et al [18] reported it as 6.2° in their study in France, which included 300 asymptomatic individuals. Although it was calculated as 3.9° in our study, as we stated in the findings, the fact that it included 1500 asymptomatic young individuals increases the value of our study.

Kwon et al [6] reported that women have significantly more lordosis in the L1 and L2 segmental Cobb angles and the global Cobb angle. Vialle et al [18] reported that lumbar lordosis is greater in women. No difference was found when we looked at the segmental and global measurements between the sexes in our study. It was seen that the segmental measurements are kyphotic at T11 and tend to lordosis as it goes down to L2, which is required by the TLJ anatomy.

In the present study, we found that both the kyphosis degree and lordosis degree increased segmentally between the 2 age groups. As a result of the kyphosis and lordosis increase, no change was observed in the sagittal Cobb angles of TLJ globally. It has been reported in the literature that the thoracic kyphosis angle increases with age [19–21]. In another study, it was found that the kyphosis in TLJ decreases with age [22]. As a result of the present study, we think the TLJ balance is trying to be preserved with the increase in lumbar lordosis in the thoracic kyphosis with age. The aim of this study was to establish reference values for the sagittal alignment of the TLJ in a healthy young adult population. While normal values for thoracic kyphosis and lumbar lordosis in the sagittal plane are well documented, there is limited research on the sagittal alignment of the TLJ. Consequently, the findings from this study can inform treatment strategies and intraoperative planning for the surgical correction of posttraumatic sagittal deformities.

The measurements in this study were made from CT scans taken while the patients were in the supine position. According to the literature, sagittal plane values measured in the supine position can differ from those measured while standing [17]. However, in trauma cases, especially in blunt traumas, the use of CT is quite useful for diagnosis after evaluation in the emergency department [3,8]. Since TLJ fractures are at the forefront for the use of the data we obtained in our study, we believe that the data obtained in the supine position will also be helpful to clinicians.

There are limitations to our study. First, the study is retrospective. In addition, the measurement of the patients included in the study from the radiographs taken only while lying down can be considered as a deficiency. However, the use of CT images taken while lying down in TLJ injuries makes the data in this study valuable. The fact that different ethnic groups were not included in the study can be a limitation, as is the fact that different values from that in the literature were found. Another limitation is the inclusion of patients in only a certain age group. Finally, the study included only patients with a body mass index between 18.5 and 30, which caused a significant portion of the population to be excluded from the study. This study has the largest number of patients in the literature. Planning this study as a multicenter prospective study with more patients and different ethnic groups can provide much more valuable data in the future.

Conclusions

This study provides information about the sagittal alignment of the TLJ in the young adult Turkish population. Additionally, we demonstrate the significant variability in physiological sagittal alignment. The findings of this study can contribute to the management of patients with posttraumatic vertebral fractures.