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Sci Rep
Sci Rep
Scientific Reports
2045-2322
Nature Publishing Group UK London

39223229
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10.1038/s41598-024-71229-1
Article
Preliminary study on the effect of lumbar axial rotation on bone mineral density measured by DXA and QCT
Zhang Zu-Zhuo 1
Hu Ting-Ting 1
Wang Yan 2
Zhu Xiao-Na 1
Liu Ying 1
Gao Lei 1
Zhang Ze-Kun 3
Gao En-Peng 1
Zhang Wei zw77988@163.com

1
Zheng Yong-Li li15733173128@163.com

1
1 https://ror.org/04eymdx19 grid.256883.2 0000 0004 1760 8442 Department of Radiology, Hebei Medical University Third Hospital, No. 139 Ziqiang Road, Qiaoxi District, Shijiazhuang, 050051 Hebei China
2 https://ror.org/04eymdx19 grid.256883.2 0000 0004 1760 8442 Department of Endocrinology, Hebei Medical University Third Hospital, No. 139 Ziqiang Road, Qiaoxi District, Shijiazhuang, 050051 Hebei China
3 https://ror.org/02qxkhm81 grid.488206.0 0000 0004 4912 1751 Department of Radiology, Hebei Provincial Hospital of Chinese Medicine, The First Affiliated Hospital of Hebei University of Chinese Medicine, Shijiazhuang, 050011 Hebei China
3 9 2024
3 9 2024
2024
14 2041729 2 2024
26 8 2024
© The Author(s) 2024
2024
https://creativecommons.org/licenses/by-nc-nd/4.0/ Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.
Currently, the relationship between axial rotation of the vertebrae and bone mineral density (BMD) measured by dual-energy X-ray absorptiometry (DXA) and quantitative computed tomography (QCT) remains controversial. The aim of this study is to quantitatively assess the effect of vertebral rotation on volumetric bone mineral density (v-BMD) and areal bone mineral density (a-BMD), further to propose the corrected strategies. To achieve this, a phantom, which was rotated from 0° to 25° in 5° increments, was utilized. Bone mineral content (BMC), a-BMD, v-BMD, and projected area (p-AREA) were measured. The Kruskal–Wallis non-parametric test or one-way ANOVA was used to examine the differences in variables between the different groups. The Pearson and Spearman correlation was used to test the relationships between quantitative parameters and rotated angles. Linear regression analysis was used to evaluate the relationship between angles and quantitative parameters. The findings indicate that, as the angle increased, a-BMD and v-BMD decreased (P < 0.001) , and the p-AREA increased (P < 0.001), but the BMC stays constant. The rotated angle was negative correlated (r = − 0.925, P < 0.001) with a-BMD and v-BMD (r = − 0.880, P < 0.001), positive (r = 0.930, P =  < 0.001) correlated with p-AREA. The linear regression analysis showed that a-BMD = 0.808–0.01 × Angle and v-BMD = 151.808–1.588 × Angle. This study showed that, axial rotation might lead to a lower measured for a-BMD and v-BMD, it should be modified. This gives clinicians some insights into how to deal with osteoporosis in scoliosis patients. It's essential for clinicians to incorporate these findings into their diagnostic processes to prevent potential misdiagnosis and over-treatment of osteoporosis.

Keywords

Scoliosis
Axial rotation
Bone mineral density
DXA
QCT
Phantom
Subject terms

Diseases
Endocrinology
Medical research
issue-copyright-statement© Springer Nature Limited 2024
==== Body
pmcIntroduction

Osteoporosis, a systemic skeletal disease characterized by low bone mass and microarchitectural deterioration of bone tissue, with a consequent increase in bone fragility and susceptibility to fractures, is common and increases as the population ages1,2. Bone mineral density (BMD) is an essential marker for assessing and identifying osteoporosis, it has been directly translated and incorporated to the management algorithms and guidelines of osteoporosis3,4. Therefore, it is particularly valuable to investigate the factors associated with BMD due to the increasing economic and social burden caused by osteoporosis5–7. With an incidence rate of approximately 2–32%, scoliosis is another common and frequently occurring disease. In older adults with osteoporosis, the incidence of scoliosis can reach as high as 60%8,9. Axial rotation of the spine as one of the main causes of scoliosis, which has a major impact on bone density. This pathological change will affect the accuracy of bone density values, affecting the diagnosis and treatment of osteoporosis10. Thus, it is essential to investigate the quantitative effects of vertebral rotation on BMD11.

In the past, there are several studies have confirmed this view, but the results are controversial12–14. Inadequate prior research has been conducted, some used adult cadaveric spines, lumbar degeneration can unavoidably impact the assessment of bone density. Some research employed phantom's shape that don't accurately represent the human spine. Since dual-energy X-ray absorptiometry (DXA) is a two-dimensional projection, the phantom's shape will unavoidably have an impact on the assessment of areal bone mineral density (a-BMD). Furthermore, DXA is considered as the gold standard for BMD measurement, it had been largely used. Quantitative computer tomography (QCT), which measures volumetric bone mineral density (v-BMD) in three dimensions, is an essential imaging technique for evaluating bone density. Does spinal rotation affect v-BMD? At present, there is limited evidence on the relationship between spinal rotation and v-BMD.

Considering these limitations, to fully match the geometry of the spine and prevent the influence of lumbar degeneration on measurement results, we utilize the trunk section of the American pediatric anthropomorphic training phantom model series 715, which matches the 5-year-old spine model perfectly. We use DXA and QCT to quantify the impact of lumbar vertebral axial rotation on a-BMD and v-BMD, attempting to obtain the correction formula between BMD and vertebral rotation angle.

Materials and methods

The trunk section of the American pediatric anthropomorphic training phantom model series 715 (Fig. 1) was used, measuring 44.5 cm (H) × 24 cm (W) × 14 cm(D), and weighting 9.85 kg. The phantom's structures contained chest, rib cage, spine, spinal disks, lungs, bronchial tree to third bifurcation, lung vasculature, trachea, scapula, clavicles, top third of humerus, pelvis and top third of femur, which were made of appropriate urethane and epoxy materials that mimic X-ray attenuation properties of human tissues for both diagnostic and therapeutic energy ranges. A specially designed rotation cradle was employed (Fig. 2), and a digital angle gauge (Fig. 3) was used to measure the angle of the rotation cradle, The phantom study did not need the approval of the ethics committee.Fig. 1 The trunk section of the American pediatric anthropomorphic training phantom model series 715.

Fig. 2 The acrylic stand designed for positioning of vertebrae.

Fig. 3 The digital goniometer shows the axial rotated angle is 15°.

DXA measurement

Phantom model underwent DXA scan of lumbar vertebrae with a GE DXA scanner (Lunar iDXA). The examination was conducted fifty time for statistical analysis, with a tube voltage of 100 kv and a tube current of 0.625 mA. The a-BMD, BMC, and p-AREA of each vertebra from L1 to L4 were recorded at 0°, 5°, 10°, 15°, 20°, and 25° angles, along with the average measurements. Two radiologists, A and B, calculated each parameter separately, and a month later, A conducted measurements in the same way to reduce measurement errors.

CT parameter measurement

Phantom model underwent CT scan of lumbar vertebrae with a 64-slice CT scanner (Siemens 64 spiral CT, Germany) with a solidstate QCT calibration phantom (Mindways Software Inc, Austin, TX, USA). The examination was conducted fifty time for statistical analysis, the scan parameters were as follows: tube voltages, 120 kV; tube current, 125 mAs; pixel, 0.78 mm2; pitch, 0.8 mm; table height, 168 cm; matrix, 512 × 512; scanning field of view (SFOV), 500 mm; and thickness,1 mm. Reconstruction parameters were standard algorithm, 1 mm section thickness and interval, and 400 mm display field of view. The scanning range was from the upper edge of 12 thoracic vertebrae to the lower edge of the 5th lumbar vertebra in the supine position. Images were transferred to a QCT workstation and analyzed using the three-dimensional (3D) spine function version 5.10 of Mindways QCT pro software (Mindways Software Inc., Austin, TX, USA). Elliptical regions of interest (ROI) were placed at the midplane of lumbar 1–3 vertebral body. The projected areal of ROI is about 250 mm2, average measurements were recorded, each parameter was calculated individually by two radiologists A and B, and one month later, doctor A measured in the same way to minimize the influence of technical error on the results.

Statistical analysis

The SPSS 26.0 statistical software package (IBM Corp, Armonk, NY, USA) was used for statistical analysis. The intra-observer and inter-observer consistency of parameters’ measurement was evaluated by intraclass correlation coefficient (ICC). ICC interpretations as poor (< 0.40), fair (0.40–0.59), good (0.60–0.74), and excellent (≥ 0.75). Statistical description of the quantitative variables were expressed as mean ± standard deviation (SD) for normal distribution data or medians (interquartile range; IQR) for non-normal distribution data. The Shapiro–Wilk test was used to test whether the data accord with the normal distribution. One-way ANOVA or Kruskal–Wallis non-parametric test was used to test the differences of variables between different angles. The correlations between a-BMD, BMC, p-AREA, v-BMD and rotated angles were analyzed using Pearson correlation test for normally distributed variables and Spearman correlation test for non-normally distributed data. Linear regression analysis was used to evaluate the relationship between the degree of rotated angles and a-BMD and v-BMD. P less than 0.05 were considered for significantly statistical differences.

Results

Distribution of DXA and QCT measurements

The a-BMD, BMC, p-AREA and v-BMD measurements of each axial rotated angle are shown in Table 1. The interclass correlation coefficients (ICC) of the test–retest reliability all achieved excellent consistency (ICC = 0.912–0.983). Table 1 Comparison of a-BMD, BMC, p-AREA, v-BMD parameters between different angle groups.

Angle	a-BMD (g/cm2)	BMC (g)	p-AREA (cm2)	v-BMD (g/cm3)	
0°	0.80 ± 0.04	4.60 ± 0.03	5.79 ± 0.03	148.90 ± 0.92	
5°	0.79 ± 0.01	4.61 ± 0.03	5.80 ± 0.03	148.78 ± 1.01	
10°	0.78 ± 0.04	4.58 ± 0.03	5.82 ± 0.03	148.19 ± 1.16	
15°	0.78 ± 0.04	4.62 ± 0.03	5.89 ± 0.03	146.83 ± 0.86	
20°	0.76 ± 0.04	4.63 ± 0.03	6.05 ± 0.05	143.63 ± 1.24	
25°	0.74 ± 0.01	4.62 ± 0.04	6.21 ± 0.03	141.16 ± 1.05	
a-BMD areal of bone mineral density of DXA, BMC bone mineral content, p-AREA projected AREA, v-BMD volumetric of bone mineral density of QCT.

Comparison of a-BMD, BMC, p-AREA and v-BMD among different vertebral rotation angles (Figs. 4, 5, Tables 2, 3)

Fig. 4 (a) Box-plot of a-BMD; and (b) Box-plot of BMC.

Fig. 5 (a) Box-plot of p-AREA; and (b) Box-plot of v-BMD.

Table 2 Changes in a-BMD, BMC, p-AREA, v-BMD according to the degree of axial rotation angle between 0° and different angle groups (%).

Angle	a-BMD	BMC	p-AREA	v-BMD	
5°	99.85	100.35	100.24	99.93	
10°	98.86	99.7	100.65	99.52	
15°	98.56	100.62	101.84	98.61	
20°	96.03	100.77	104.64	96.46	
25°	93.21	100.42	107.41	94.80	
a-BMD areal of bone mineral density of DXA, BMC bone mineral content, p-AREA projected AREA, v-BMD volumetric of bone mineral density of QCT.

Table 3 Changes in a-BMD, BMC, p-AREA, v-BMD between 0° and different axial rotated angle groups (P value).

Angle (°)	5	10	15	20	25	
a-BMD (g/cm2)	1.000	 < 0.001*	 < 0.001*	 < 0.001*	 < 0.001*	
BMC (g)	0.285	1.000	0.001*	 < 0.001*	0.072	
p-AREA (cm2)	1.000	0.015*	 < 0.001*	 < 0.001*	 < 0.001*	
v-BMD (g/cm3)	1.000	0.461	 < 0.001*	 < 0.001*	 < 0.001*	
a-BMD areal of bone mineral density of DXA, BMC bone mineral content, p-AREA projected AREA, v-BMD volumetric of bone mineral density of QCT.

In our facility, when the rotated degree reached 10°, the a-BMD fell by 1.14% relative to the baseline value, and the difference is statistically significant (P < 0.001). The a-BMD can decrease up to 6.79% in relation to the baseline when the rotation angle reaches 25°(P < 0.001). When the rotation angle reaches 10°, the p-AREA starts to rise by 1.84% compared to the baseline value, the rotational angle increases by 7.41% when it reaches 25° (both P < 0.001). When the rotational degree reaches 15°, the v-BMD continues to decrease, 1.39% less than the baseline, and it drops by 6.2% when it achieves 25° (both P < 0.001).

Correlation between a-BMD, BMC, p-AREA, v-BMD and axial rotated angle are shown in Table 4

Table 4 Correlation analysis between a-BMD, BMC, p-AREA, v-BMD and angle.

Angle	a-BMD	BMC	AREA	v-BMD	
r	− 0.925	0.281	0.930	− 0.880	
P	< 0.001*	< 0.001*	< 0.001*	< 0.001*	
a-BMD areal of bone mineral density of DXA, BMC bone mineral content, p-AREA projected AREA, v-BMD volumetric of bone mineral density of QCT.

Rotated angles was negatively correlated with a-BMD (r = − 0.925, P < 0.001), positively correlated with p-AREA (r = 0.930, P < 0.001), and negatively correlated with v-BMD (r = − 0.880, P < 0.001).

Correction formula between BMD and vertebral rotation angle (Fig. 6)

Fig. 6 (a) Linear regression analysis between a-BMD and axial angle; and (b) Linear regression analysis between v-BMD and axial angle.

Linear regression analysis showed that a-BMD = 0.808–0.01 × Angle means that a-BMD falls by 0.01 g/cm2 for every degree that the rotation angle increases. v-BMD = 151.808–1.588 × Angle shows that v-BMD falls by 1.588 g/cm3 for every degree increase in rotation angle.

Discussion

This study encompassed a phantom aimed to investigate the correlation between axial rotation of the lumbar BMD. The objective of this research was to ascertain whether the degree of vertebral rotation angle was associated with BMD. In the context of our findings, the impact of the axial rotation can lead to a decrease in BMD.

Scoliosis is caused by two factors: axial rotation and lateral curvature. While axial rotation has received less emphasis in research, most studies have focused on lateral curvature15,16. In addition, previous studies about the effect of lumbar spinal rotation on BMD have used simple phantom, cadaver or scoliosis patients. These studies have some limitations, such as some confounding factors in human studies, such as potential diseases and the effects of drug or surgical treatment, facet osteoarthritis and end-plate sclerosis, which may have a significant impact on BMD evaluation17–20. On the other hand, the basic phantom used in earlier research does not match the vertebral body's shape, which will lead to measurement inaccuracies for these metrics12. In view of these limitations, we used the American pediatric anthropomorphic training phantom model series 715 to lessen the aforementioned confounding factors, which is consistent with the typical lumbar structure. Moreover, previous studies on this subject were limited to DXA, no research on the effect of axially rotated angles on v-BMD could be found. Presently, there is limited evidence on the relationship between spinal rotation and v-BMD. Therefore, we used the American paediatric anthropomorphic training phantom model series 715, which matches the 5-year-old spine model perfectly, was scanned by DXA and QCT, to investigate the effects of lumbar axial rotation on a-BMD and v-BMD.

In this study, we discovered that the a-BMD gradually decreased and the P-AREA gradually increased as the angle increased, consistent with the majority of other research. For example, Cheng's study17 using four cadaver specimens ranging in age from 17 to 40 years, with the rotation angle (rotation angle 0°–45°, in increments of 7.5°), discovered that the degree of rotation significantly correlated with both the a-BMD and p-AREA, with the correlation for the former being negative (r = − 0.655, P < 0.001) and the latter being positive (r = 0.747, P < 0.001). Furthermore, in another similar study by Girardi13 used a male cadaver spine with rotation angle 0°–60° in increments of 10°, discovered that as the rotation angle increased from 0° to 50°, the a-BMD value decreases gradually (r = 0.92, P < 0.001), and the p-AREA increases gradually (r = 0.73, P < 0.001), which were similar to our study. However, in Jeon's12 study, they found that an axial rotation angle greater than 5° caused an overestimation of a-BMD and the degree was positively correlated with a-BMD and negatively correlated with P-AREA. We speculate that the reason may be the phantom in Jeon's12 study is a GE Lunar Aluminium Spine Phantom, which is not a perfect replica of the human spine unlike the human spine, and lacking posterior components and transverse processes, as the axial rotation angle increases. But in the current study we employed a phantom that holds a similarity to the human lumbar vertebra. Perhaps due to the spinous process is rotated to the pedicle border or outside the vertebral body margins, a component of the transverse processes and the posterior column included in the projected area during rotation, which leads to the increase of p-AREA (Fig. 7). Since a-BMD is calculated as the ratio of BMC to the p-area, so that the a-BMD was decreased.Fig. 7 Dual energy X-ray absorptiometry measurements for the neutral position and for vertebral axial rotation in increments of 5 degrees per scan, up to 25 degrees rotation.

In contrast to earlier research, our study has the advantage of using smaller incremental intervals (5° as opposed to 7.5° and 10°). The reason for that, there is no solution for rectifying a-BMD has been proposed by the aforementioned scholars, perhaps due to rotational angle observed is too large, and trend of BMD changes has not been investigated thoroughly. Furthermore, the degree of rotation is frequently within 25° in clinical settings19–21, so it makes more sense for patients to analyze angle changes within 25°. Therefore, in the present study, we made reference to the previously mentioned studies, and proposed the methods of calibration, a-BMD = 0.808–0.01 × Angle.

Moreover, DXA has been used in previous studies to assess BMD and body composition, even though DXA is still the gold standard for diagnosing osteoporosis. QCT, which measures the volumetric of BMD, can assess BMD more accurately than DXA, avoiding the effects of endplate sclerosis, facet degeneration, vertebral osteophyte, vertebral stenosis and abdominal aortic wall calcification22,23. In addition, QCT performs more accurately and sensitively than DXA. The results regarding v-BMD exceeded our expectations as we initially assumed that QCT would use three-dimensional volume expansion analysis to evaluate bone density, and its accuracy should be independent of vertebral rotation. But in this study, we found that when the rotational degree reaches 15°, the v-BMD continues to decrease, 1.39% less than the baseline value, and it drops by 6.2% when the degree achieves 25° (both P < 0.001). The regression analysis results shows that v-BMD falls by 1.588 g/cm3 for every degree increase in rotation angle.

As we know, the fundamental process of QCT measurement of BMD involves measuring the lumbar trabecular bone's CT value, then converting it to BMD using the phantom's CT value. The CT value is associated with tissue density, X-ray energy and algorithm, CT value = (X ray attenuation coefficient of a substance-water attenuation coefficient)/water attenuation coefficient × 100024,25.The formula for converting BMD to CT value is V-BMD = [(Hb − Hw)/(Hk − Hw)] × Ck, Ck represents the concentration of bone mineral substitutes in the QCT model material, while Hb, Hk and Hw represent the CT values of bone, QCT model and water, respectively26,27. We speculated the reason for the decrease in v-BMD with increasing angle may be that as the angle increases, the X-ray's attenuation coefficient decreases due to the increased distance from the spherical tube to the detector through the phantom. This, raises the CT value and v-BMD. Secondly, the change in voltage through the phantom tube caused by axial rotation may also be one of the reasons. But this is merely a hypothesis, and more investigation is needed to confirm the accurate findings.

Limitations

There are some limitations in the present study. Firstly, while the phantom employed in this study reflects the anatomical structure of the human spine in terms of shape, proportion, structure and density, it is not a perfect replica of human structure. Secondly, not all clinical pathogenic abnormalities, including sagittal and coronal lateral scoliosis, could be replicated by this study since it focused on the axis rotation angle of the lumbar spine, which is different from the actual clinical situation. Thirdly, due to the limitation of phantom, the effect of under different bone mass conditions was not analyzed. Finally, due to limitations of the rotating device prevent us from measuring a larger rotation angle. We intend to include more variables, such age, gender and BMI in the clinical studies. Subsequent investigations will be included larger rotation angles and stratified according to different bone mass and age groups. In addition, we will incorporate clinical data from real patients in order to corroborate the results of the phantom study and modify the correction equations in light of practical circumstances.

Conclusions

This study demonstrates a negative correlation between axial rotation of the lumbar and BMD, axial rotation of the lumbar spine can result in recorded values of a-BMD and v-BMD being lower than the true values, with critical angles of 10° and 15°, respectively. In the assessment of BMD for patients with axial rotation, BMD of the lumbar should be interpreted critically due to artifacts arising from the axial rotation of the spinal. In order to prevent overestimating a patient's osteoporosis severity and negatively affecting diagnosis and therapy, clinicians should be aware of this fact when diagnosing and treating osteoporosis patients.

Acknowledgements

We would like to thank the anonymous reviewers for their helpful remarks.

Author contributions

Z.-Z.Z., has wrote the main manuscript text and prepared all figures and tables. T.-T.H., X.-N.Z., E.-P.G. analyzed data. Y.W. and Z.-K.Z. interpreted results of experiments. Y.L., L.G. reviewed, edited and revised manuscript. Y.-L.Z. and W.Z. contributed to the study conception and design, and contributed equally to this work and should be considered co-corresponding authors.

Data availability

Correspondence and requests for materials and data should be addressed Y.-L. Z. and W.Z.

Competing interests

The authors declare no competing interests.

Publisher's note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

These authors contributed equally： Wei Zhang and Yong-Li Zheng.
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