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16 July 2024: Clinical Research  

Gender-Specific Risk Factors for Asymmetric Bone Density in Adult Degenerative Lumbar Scoliosis: A Retrospective Cohort Analysis

Junchuan Liu1ABCDEF, Wenshuai Li2BCDF, Congjie Li2BCDF, Jun Di1BDEF, Junfei Guo3ABCDEF, Linfeng Wang2ACDEFG*

DOI: 10.12659/MSM.944137

Med Sci Monit 2024; 30:e944137

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Abstract

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BACKGROUND: This study aimed to evaluate the performance of Hounsfield Unit (HU) value on the vertebral bone mineral density associated with adult degenerative lumbar scoliosis (ADLS) and to compare the HU and coronal height changes of the lumbar spine on the concave and convex sides. The secondary aim was to investigate the risk factors for increased asymmetric ratio of HU (ARH) by concave-to-convex.

MATERIAL AND METHODS: A total of 74 patients aged ≥50 years were retrospectively reviewed. The height and the HU values of the region of interest were measured and compared. Multiple linear regression and gender-stratified analyses were performed to explore risk factors. Restricted cubic spline (RCS) was used to visually assess the dose-effect relationship between the Cobb angle and ARH.

RESULTS: The heights on the concave sides were significantly lower while HU values were significantly higher than that of the convex side. Cobb angle (95% CI: 0.001 to 0.009, P=0.034) was positively correlated with the increased ARH, while apex orientation to the right (95% CI: -0.152 to -0.013, P=0.022) was negatively associated. Gender-stratified analyses showed age and apex vertebrae location are 2 additional risk factors in male patients but not in female patients. Cobb angle was identified by RCS as a risk factor both in males and females and the inflection points were 15 and 17.5, respectively.

CONCLUSIONS: HU values on the concave side are significantly higher than on the convex side, showing the asymmetrical bone mass distribution of ADLS patients. Several gender-related risk factors for increased ARH have been identified.

Keywords: Risk Factors, Osteoporosis, Bone Diseases, Metabolic, orthognathic surgery, Spine, Humans, Male, Scoliosis, Female, Retrospective Studies, Lumbar Vertebrae, Middle Aged, Aged, Bone Density, Sex Factors, Tomography, X-Ray Computed

Introduction

Adult degenerative lumbar scoliosis (ADLS) is a common spinal disease that primarily affects elderly patients, causing symptoms such as low back pain, lower extremity pain, and intermittent claudication [1–3]. The diagnosis and management of ADLS are becoming increasingly crucial as the global population ages and the prevalence of osteoporosis (OP) rises [4]. It is projected that by 2050, 16.7% of the world’s population will be aged 65 years and over. In China, the number of individuals aged 60 and above was roughly 250 million in 2018, accounting for almost 20% of the total population. This number is expected to climb to nearly 450 million, or roughly 30% of the population, by 2050 [5,6]. This demographic shift is associated with higher incidences of OP, reported in 30–40% of females and 10–20% of males among China’s aging population [7,8].

Previous studies have explored various aspects of ADLS and its association with OP. The asymmetric degeneration of the intervertebral disc on the convex and concave sides of the spine is the primary cause of ADLS, resulting in coronal and sagittal changes in the lumbar spine and making the disease worse [9,10]. Biomechanical imbalances in scoliosis cause asymmetric bone damage and remolding of vertebral microstructure, leading to reduced bone toughness and ultimately contributing to ADLS exacerbations [11,12]. Previous studies have explored the relationship between osteoporosis and degenerative spinal conditions, but the current criterion standard for diagnosing OP, dual-energy X-ray absorptiometry (DXA), may not accurately reflect the presence of OP in vertebral bone mineral density (VBMD) in elderly ADLS patients, leading to falsely elevated scores [4,13–15]. This limitation arises due to the inability of DXA to exclude the influence of factors such as cortical bone, abdominal wall vascular calcification, osteophyte hyperplasia, articular process hyperplasia, and degenerative lumbar changes [16–18]. In contrast, recent advancements have highlighted the potential of using Hounsfield Units (HU) derived from vertebral CT scans as a more accurate measure of VBMD and prevent degenerative conditions and cortical bone in 3-dimensional CT images [19–22]. Schreiber et al and Zou et al [20,21] demonstrated a significant correlation between HU values and DXA T-scores, suggesting HU is a reliable indicator for osteoporosis screening. Additionally, Wang et al revealed that HU measurements can detect differences in bone mass between the concave and convex sides of the vertebral body, offering a unique advantage over DXA in assessing asymmetrical vertebral degeneration in ADLS [22].

Despite these advancements, there remains a gap in research specifically addressing the application of HU values in evaluating VBMD in ADLS patients and identifying risk factors for increased asymmetric ratio of HU. This study aimed to fill this gap by evaluating the performance of HU values on VBMD associated with ADLS and correlating HU differences with coronal height changes on the concave and convex sides. We investigated the gender-specific risk factors for increased asymmetric ratio of HU, providing new insights that could inform future treatment strategies for ADLS.

Material and Methods

STUDY DESIGN, SETTING, AND POPULATION:

A retrospective analysis was conducted on all ADLS patients aged over 50 years old at an urban, Level I spine center ranked among the top 10 in China, between Jan. 2018 and Aug. 2021. We enrolled patients with full-spine posteroanterior X-ray and three-dimensional (3D) CT scanning, diagnosed with ADLS based on physical examination and whole-spine radiography (Cobb angle ≥10°) [23]. Patients with adult idiopathic scoliosis were excluded to maintain a homogeneous study population focusing solely on degenerative lumbar scoliosis. We excluded patients with lumbar spinal trauma, tuberculosis, tumor, ankylosing spondylitis, or skeletal hyperostosis, those with a history of lumbar surgery, and patients with spinal infections or other metabolic diseases that can affect bone metabolism and accuracy of HU measurements. The study was overseen and approved by the institutional internal review board of the participating institution (2022-115-1) in compliance with the Declaration of Helsinki, and all patients involved gave informed consent. All collected patient data were anonymously recorded to protect patient confidentiality.

VBMD EVALUATION:

All included patients underwent full-spine posteroanterior X-ray and 3D reconstructive CT (tube voltage of 120 kV, Siemens Somatom Force, Siemens AG, München, Germany) with a slice thickness of 1.25 mm with 0.625 mm intervals, and picture archiving and communication system software (PACS workstation, Guanzhou, China) was used to calculate HU value with only cancellous bone and avoiding cortical edges, osseous abnormalities, and voids to prevent volume averaging. The HU value for each vertebra was measured using the method described by Schreiber for regions of interest (ROI) and were measured by JCL, WSL, and CJL, who were responsible for all radiological measurements, which were made 3 times in 3 horizontal planes (upper, middle, and lower 1/3) to give a mean HU value for each vertebral body to ensure accuracy and reliability [21]. After training of ROI drawing, the HU values of L1 to L5 in each patient, and then HU measurements within both sides of concave and convex were obtained separately in the lower end vertebrae, apex vertebrae, and upper end vertebrae on the upper 1/3, middle, and lower 1/3 sides. Each parameter was averaged to give a mean value for statistical analysis (Figures 1, 2). A cut-off value of ≤110 HU at L1 vertebral body was used for diagnosing osteoporosis according to the current dichotomizing threshold recommended in the literature [3,22,24,25]. All radiological parameters were measured by 2 independent observers and all measurements were performed 3 times, from which the mean value was calculated for further statistical analysis.

DATA COLLECTION AND DEFINITION:

Using our institution’s electronic medical records, we retrospectively collected demographic information on our patients, including age, age group (51–60, 61–70, and >70), gender, body mass index (BMI), BMI group (normal with BMI <24, overweight with 24≤ BMI <28, and obesity with BMI ≥28), direction of scoliosis, Cobb angle of the scoliotic vertebral body, apex vertebrae group (2–3, 3, 3–4, and 4), the height and HU value of both sides of the total scoliosis-related vertebrae and apex vertebrae, and the height from the upper end edge to the lower end edge of the lower apical vertebra were recorded. On the basis of the full-spine posteroanterior radiographic evaluation, the asymmetric height ratio and asymmetric HU ratio were calculated by measuring the concave/convex ratio between the most tilted vertebrae and the Cobb angle between the 2 most tilted vertebrae.

STATISTICAL ANALYSIS:

Testing for normality was performed by applying the Shapiro-Wilk test to continuous variables. Continuous variables were recorded as mean±standard deviation (SD), and the t test was used to analyze the difference of normally distributed samples. Paired t tests were used to analyze the difference of heights and HU values between concave and convex sides within the target vertebrae. Categorical variables were expressed as number and percentages (%), processed by chi-square test or Fisher’s exact test. Multiple linear regression analyses were performed on all patients and then stratified by gender, encompassing all characteristics that could possibly be correlated with the asymmetric ratio of HU by concave/convex as candidate predictor variables. In the multicategory variables, 51–60 years of age, normal BMI, and L3–4 of apex vertebrae location which contained the highest number of individuals were chosen as standard, and the others were converted into dummy variables.

Restricted cubic spline (RCS) with 4 knots and adjusted by all covariables with P value <0.1 was used to visually assess the dose-effect relationship between the Cobb angle and asymmetric ratio of HU by concave/convex ratio. We conducted RCS with 4 knots at the 5th, 35th, 65th, and 90th centiles to flexibly model the association. The reference value was set depending on the RCS shape. The data were then stratified into 2 groups based on the inflection point, and segmented linear regression analysis was then performed on both groups separately. Pearson correlation coefficients were calculated to evaluate the correlations between the asymmetric ratio of HU by concave/convex and the asymmetric ratio of height by concave/convex in all scoliosis-related vertebrae and apex vertebrae. To assess the reproducibility of HU measurements, we calculated intraclass correlation coefficients (ICC) along with 95% confidence intervals. The ICC showed inter-observer and intra-observer reliability calculations, reported as a score between 0 and 1 (0 representing no agreement and 1 representing perfect agreement). It was defined as very strong with ICC ≥0.80 [26]. To corroborate our analyses, we performed 2 sets of leave-one-out sensitivity analyses. All data analyses were performed using IBM SPSS Statistics for Windows, version 26.0 (IBM, Armonk, NY, USA). RCS analyses were performed using R software (R Core Team, version 4.2.2), along with the use of the rms package. A 2-sided P value <0.05 was considered significant.

Results

CHARACTERISTICS OF THE PATIENTS:

Within the study period, data from 74 patients with a total of 259 vertebral bodies who met the inclusion criteria were retrospectively reviewed and included in the final analysis. There were 22 males and 52 females, with a mean age of 63.2±5.2 years and BMI 22.7±2.9 kg/m2. Fifty-one patients (68.9%) had apex orientation toward the left, while 23 patients (31.1%) had apex orientation toward the right. The mean Cobb angle was 18.9±7.4° in all patients. The apex vertebra was located mostly in L3/4 in 27 patients (36.49%), followed by L2/3 in 24 patients (32.43%), L3 in 17 patients (22.97%), and L4 in 6 patients (8.11%). The scoliosis contained 4 vertebral bodies in 33 patients (44.59%), 3 vertebral bodies in 38 patients (51.35%), and 5 vertebral bodies in 3 patients (4.06%).

The gender-related distribution of patient characteristics is summarized in Table 1. There were no significant differences regarding age, age group, gender, BMI, BMI group, apex orientation, Cobb angle, apex vertebrae group, asymmetric ratio of height by concave/convex, or asymmetric ratio of HU by concave/convex between male and female patients (all P>0.05).

COMPARISON OF VALUES AND ASYMMETRIC RATIOS OF HEIGHT AND HU IN TOTAL SCOLIOSIS-RELATED VERTEBRAE AND APEX VERTEBRAE:

Inter-observer and intra-observer reliability of the measurement of the HU values were excellent, with a mean ICC value of 0.908 (range, 0.896 to 0.922) and 0.932 (range, 0.912 to 0.956), respectively (data not shown). The strong reliability of HU values suggests it is a reliable indicator for evaluating VBMD in ADLS patients, with both inter-observer and intra-observer reliability of ICC values over 0.80. Table 2 shows the comparisons of height and HU values within concave and convex sides of all scoliosis-related vertebrae (on average) and apex vertebrae. The heights on the concave sides of both total scoliosis-related vertebrae (on average) and apex vertebrae were lower and the HU values on the concave side were higher than that of the convex side, with all results statistically significant (all P<0.001).

Asymmetric ratios of height and HU were defined as the ratio of the values of height and HU within the concave/convex side, respectively. The mean asymmetric ratio of height in total scoliosis-related vertebrae (n=259) was 0.91±0.11, while the mean asymmetric ratio of HU of that was 1.28±0.31, with the Pearson correlation coefficient of −0.585 (P<0.001). The mean asymmetric ratio of height in the apex vertebrae (n=124) was 0.85±0.10, while the mean asymmetric HU ratio was 1.40±0.33, with a Pearson correlation coefficient of −0.471 (P<0.001). Correlation analysis showed that HU value was negatively correlated with the height of the apex vertebrae and all scoliosis-related vertebrae on average.

ANALYSIS OF POSSIBLE FACTORS INFLUENCING THE ASYMMETRIC RATIO OF HU BY CONCAVE/CONVEX:

To examine the association between the asymmetric ratio of HU by concave/convex and all factors that it could causatively be related to, we performed multiple linear regression on all patients, male patients, and female patients. As shown in Table 3, the factors associated with a higher asymmetric ratio of HU in all patients were Cobb angle (95% CI: 0.001 to 0.009, P=0.034), while apex orientation to the right (95% CI: −0.152 to −0.013, P=0.022) was correlated with a lower asymmetric ratio of HU. As a result, the mean contribution to the asymmetric ratio of HU was −0.082 in patients with apex orientation to the right and 0.005 per 1º of Cobb angle increased. As shown in Figure 3, the adjusted RCS showed an increasing trend for asymmetric ratio of HU with the increase in Cobb angle, where the test for nonlinearity showed no statistical significance. The inflection point of the RCS curve was identified at Cobb angle=17, representing a turning point in the relationship between the Cobb angle and the asymmetric ratio of HU (Figure 3). Using the inflection point, the data were stratified into 2 groups: Cobb angle <17 and Cobb angle ≥17. Segmented linear regression analysis was then performed on both groups separately. The results showed the adjusted coefficients of Cobb angle level on asymmetric ratio of HU were 0.01 (95% CI: 0.00 to 0.01, p<0.001) before standardization and 0.58 (95% CI: 0.32 to 0.85, P<0.001) after standardization.

For male patients, age (95% CI: 0.020 to 0.053, P<0.001), 61–70 years of age (95% CI: 0.140 to 0.489, P=0.002), Cobb angle (95% CI: 0.014 to 0.046, P=0.002), apex vertebrae located at L2/3 (95% CI: 0.042 to 0.248, P=0.010), and apex vertebrae located at L3 (95% CI: 0.027 to 0.205, P=0.015) were correlated with the increased asymmetric ratio of HU, while apex orientation to right (95% CI: −0.255 to −0.042, P=0.009) was correlated with the decreased asymmetric ratio of HU (Table 4). As a result, the mean contribution to the asymmetric ratio of HU was −0.148 in patients with apex orientation to the right, 0.036 per 1 year increase, 0.314 in patients 61–70 years of age, 0.030 per 1 degree of Cobb angle increased, 0.145 in patients with apex vertebrae located in L2/3, and 0.116 in in patients with apex vertebrae located in L3. As shown in Figure 4, the adjusted RCS showed an increasing trend for asymmetric ratio of HU with the increase in Cobb angle, where the test for nonlinearity showed no statistical significance. The inflection point of the RCS curve was identified at Cobb angle=15, representing a turning point in the relationship between the Cobb angle and the asymmetric ratio of HU (Figure 4). Using the inflection point, the data were stratified into 2 groups: Cobb angle <15 and Cobb angle ≥15. Segmented linear regression analysis was then performed on both groups separately. The results showed the adjusted coefficients of Cobb angle level on asymmetric ratio of HU were 0.02 (95% CI: 0.00 to 0.03, P=0.021) before being standardized and 0.23 (95% CI: 0.12 to 0.44, P<0.001) after being standardized.

Table 5 shows only Cobb angle (95% CI: 0.002 to 0.013, P=0.012) was correlated with the increased asymmetric ratio of HU in female patients but not males. As a result, the mean contribution to the asymmetric ratio of HU was 0.007 per one degree of Cobb increased. As shown in Figure 5, the adjusted RCS showed an increasing trend for asymmetric ratio of HU with the increase in Cobb angle, where the test for nonlinearity showed no statistical significance. The inflection point of the RCS curve was identified at Cobb angle=17.5, representing a turning point in the relationship between the Cobb angle and the asymmetric ratio of HU (Figure 5). Using the inflection point, the data were stratified into 2 groups: Cobb angle <17.5 and Cobb angle ≥17.5. Segmented linear regression analysis was then performed on both groups separately. The results showed the adjusted coefficients of Cobb angle level on asymmetric ratio of HU were 0.01 (95% CI: 0.01 to 0.01, P<0.001) before standardization and 0.71 (95% CI: 0.43 to 0.99, P<0.001) after standardization. Our findings remained similar in sensitivity analyses, where we restricted our analyses to all patients with normal BMI/overweight or males/females with normal BMI or overweight (data not shown).

Discussion

In this study, we aimed to evaluate the performance of HU values on VBMD associated with ADLS and to investigate the risk factors for increased asymmetric ratio of HU. Our results revealed that HU values on the concave side of the lumbar vertebral body were significantly higher than those on the convex side, indicating asymmetrical bone mass distribution in ADLS patients. Additionally, the heights on the concave sides were significantly lower compared to the convex sides. There was a positive correlation between the Cobb angle and the increased asymmetric ratio of HU, showed that vertebral body remodeling is influenced by asymmetric loading, leading to compensatory changes in bone density. Apex orientation to the right was negatively associated with the asymmetric ratio of HU. For gender-specific risk factors, in male patients, age and apex vertebrae location were identified as additional risk factors for increased asymmetric ratio of HU, while in female patients only the Cobb angle showed a significant correlation, indicating that the severity of scoliosis curvature is the predominant factor influencing bone mass asymmetry in women. This difference between genderes may be attributed to distinct biomechanical and hormonal influences on bone metabolism. These findings highlight the importance of considering asymmetrical bone mass distribution and specific risk factors when assessing and managing ADLS patients.

Osteoporosis, which is a degenerative bone condition associated with reduced bone strength and mass, is most common in older adults. OP has been reported to occur in 30–40% of females and 10–20% of males in the general elderly Chinese population [7,8], and as living standards continue to improve, the incidence of degenerative lumbar scoliosis is on the rise among the elderly [27]. The vertebral degeneration associated with OP remains the predominating factor of ADLS [4,28–30]. Vanderpool et al [29] reported the incidence of ADLS in patients with OP was approximately 6 times higher than in people with normal metabolism. However, Urrutia et al [31] revealed that age and BMI were 2 independent risk factors for ADLS by observing postmenopausal women aged 50 years and older, while VBMD was not an independent predictor of the magnitude of the curve. In addition, Wang et al [22] also indicated the progression of degenerative scoliosis had no correlation with osteoporosis based on HU measurement.

Recently, in light of the fact that DXA measurements of VBMD may indicate a lower prevalence of OP in degenerative spine conditions [14,20], HU values detected by clinical CT scanning have been widely studied to evaluate the VBMD and screen for OP, with excellent reliability and significant correlation with DXA T-scores [21,25,32–34]. Regarding the use of imaging techniques, it is important to clarify that while MRI is commonly used for the preoperative evaluation and planning of spine surgery due to its superior soft-tissue contrast, CT scans play a crucial role in specific contexts. CT is often utilized when there is a need to assess bone abnormalities, such as in cases of congenital scoliosis, or when precise anatomical detail is required for surgical navigation systems. Although CT scans involve higher radiation doses compared to standard imaging techniques, the detailed bone visualization they provide is essential in certain clinical scenarios. It is also important to recognize the advancements in CT technology, which have led to protocols that optimize image quality while minimizing radiation exposure. In the current study, we aimed to evaluate the performance of HU values on the VBMD associated with ADLS and to investigate the risk factors of increased asymmetric ratio of HU measured by concave/convex ratio.

We found the HU value was negatively correlated with the height in apex vertebrae and total scoliosis-related vertebrae. In other words, there was a higher HU value on the concave side of the lumbar vertebral body than on the convex side on the horizontal plane, indicating that the vertebral body remodeling may be irregular due to asymmetrical loading. Our findings are in line with previous reports [3,22] that VBMD on the concave side is higher than on the convex side, indicating that the bone metabolism on both sides of the lumbar vertebrae in ADLS patients is inconsistent. In a previous finite element analysis study, Song et al [35] demonstrated that on the concave side of the major curve of the spine, the mechanical load was greater than on the convex side. Therefore, the asymmetric ratio of HU with loss of height on the concave side (for a curve to develop) can be due to either asymmetric disc degeneration or from the vertebral body. The loss of height from vertebral body collapse may have falsely elevated the HU values or may be due to compensatory remodeling in response to the deformity. The increased HU or the asymmetric ratio of HU and scoliosis are therefore complementary.

To the best of our knowledge, this is the first study to investigate the factors associated with increased asymmetric ratio of HU. According to our results, Cobb angle was identified as a risk factor for increased asymmetric ratio of HU in all patients, while apex orientation to the right was a protective factor. A possible explanation is that 95% of the patients were right-handed in this study. Multiple linear regression analysis was performed separately for male and female patients and found that age and apex vertebrae location were 2 risk factors, while apex orientation to the right was a protective factor in male patients but not in female patients. When interpreting the results of an RCS analysis, the inflection point (the point where the curve changed its direction) was set as a cut-off value. The inflection point represented a turning point or boundary between different patterns of association between the predictor variable and the outcome. In cases where the RCS analysis revealed a U-shaped, inverted U-shaped, or L-shaped curve, with a clearly identifiable inflection point, the data were divided into 2 distinct segments based on this inflection point. This segmented linear regression allowed for a more nuanced understanding of the relationship between the predictor variable and the outcome in each segment, as it accounted for the distinct patterns of association in different parts of the curve. As expected, Cobb angle was identified as a risk factor in both males and females and the inflection points were 15 and 17.5, respectively.

Regarding the associations between the asymmetric ratio of HU and age, apex vertebrae location, and apex orientation to the right were more prominent in males than in females, the difference may be explained by asymmetric loading in ADLS patients, which can increase bone resorption. Our results suggest that males and females have different bone structures. The conclusion seems to be contrary to the previous study by Ho-Pham et al [36]. However, finite element analysis by Amin et al [37] revealed that in women with a recent or osteoporotic fracture, mean total hip vBMD values tended to be higher than in men with the same fracture history, despite the fact that women with osteoporotic fractures were slightly older than men. In fact, there was a lack of awareness, inadequate specific knowledge, and poor practice about osteoporosis in males, as has been previously recognized [38]. Female patients scored significantly higher than males in terms of general knowledge regarding osteoporosis. It is imperative that osteoporosis prevention programs target older Chinese men to improve their knowledge, health beliefs, and practices.

There is no uniform conclusion about changes in HU values at all levels of the lumbar spine. Schreiberet and Demiret [21,39] found no significant difference in HU values from L1 to L4 through CT measurements. Conversely, Wang et al [22] found the HU value gradually increased from L1 to L5 and presented no correlation with the progression of ADLS. The present study did not find a change in tendency of HU values from L1 to L5. However, we found the HU values were higher on the concave side than on the convex side in patients with ADLS, and the increased asymmetric ratio of HU, which represents asymmetrical vertebral degeneration, was closely related to the progression of degenerative scoliosis, especially in the apex vertebrae. We speculate that the self-healing mechanism is activated, which eventually leads to a decrease of height and an increase of HU value on the concave side. This is also in accordance with Wolff’s Law of Bone [3,40], which states that repeated loads on the bone elicit adaptive responses that allow the bone to better cope with these loads. Furthermore, the osteophyte hyperplasia on the concave side observed in some cases can also reflect the strong bone metabolism. Nevertheless, it does not imply that a patient with ADLS is not osteoporotic, since the concomitant alteration is the increased HU value on the concave side. Hence, our results need to be interpreted with caution.

Analysis of the significance of bone metabolism on both sides of the lumbar spine in patients with ADLS also makes a significant impact on surgical treatment because good bone density could play a decisive role in having greater resistance to screw pull-out. A study by Lim et al [41] demonstrated that BMD in the vertebral body region affects the success of various implanted devices. Zou et al [42] concluded that HU value was a better predictor of pedicle screw loosening than T-score. Other researchers [24,43–45] also shown lumbar HU measurement has advantages in the prediction of osteoporotic fractures, cage subsidence, and adjacent segment fracture. According to our results, the stability of internal fixation is better diverted from the concave side due to the higher bone density, which can reduce the incidence of postoperative internal fixation failure, but this needs to be confirmed by further mechanical experiments or finite element analysis.

Our results may have several limitations. First, it was retrospective and observational, and only focused on patients 50 years of age or over. A second and main limitation is the single-center setting with a small number of patients, which may limit the generalizability of the results. Third, measurements of HU values were performed manually, which lacks accuracy. However, the HU value for each vertebra in this study was measured using the method of ROI from the 3 horizontal slices to obtain a mean value. In addition, a strong correlation between HU values and ADLS suggests HU can be a reliable indicator for evaluating VBMD. Previous studies also demonstrated that HU values allow for avoiding vertebral degenerative changes and directly measuring cancellous bone in vertebral bodies, which is more sensitive than DXA [3,20,25]. Furthermore, we did not calculate asymmetric HU ratio subgroup values for different apex vertebrae subgroups due to the small sample size. With recent advances in computer technology, finite element analysis is becoming a more reliable method in developing orthopedic treatment strategies. The application of finite element analysis can be advantageous and will bring more benefits in the future.

Conclusions

HU values measured by CT on the concave side were significantly higher than those of the convex side of the lumbar vertebral body on the horizontal plane, showing the asymmetrical bone mass distribution of ADLS patients. Age, Cobb angle, and apex vertebrae located at L2/3 and L3 were correlated with the increased asymmetric ratio of HU, while apex orientation to the right was correlated with the decreased asymmetric ratio of HU for male patients. In female patients, only Cobb angle was correlated with the increased asymmetric ratio of HU.

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