Difference and Correlation Between Standing and Supine Cervical Sagittal Alignment: DTS vs MRI

Abstract

Study design

Retrospective study.

Objectives

This study aimed to measure cervical sagittal alignment parameters on upright digital tomosynthesis (DTS) and supine magnetic resonance imaging (MRI) in patients with cervical spondylotic myelopathy (CSM) and evaluate the difference and correlation of cervical curvature in different postures.

Methods

101 CSM patients underwent both standing DTS and supine MRI. Parameters including O-C2 angle, cervical lordosis (CL), C2-7 sagittal vertical axis (C2-7 SVA), neck tilt (NT), T1 slope (T1S), thoracic inlet angle (TIA), cervical tilt, and cranial tilt were measured. Intraclass correlation coefficients (ICC) was used to assess inter-observer reliability. Paired t-tests and Pearson correlation analyses were applied to investigate the difference and correlation of parameters in standing and supine position.

Results

All parameters measured on DTS and MRI showed excellent reliability (ICC >0.8). Significant differences were observed in O-C2 (DTS: −24.2 ± 11.2° vs MRI: −14.3 ± 6.6°, P < 0.001), CL (DTS: −15.2° ± 4.4° vs MRI: −8.1° ± 3.6°, P < 0.001), C2-7 SVA (DTS: 23.6 ± 11.0 mm vs MRI: 16.5 ± 8.5 mm, P < 0.001), T1S (DTS: 26.3° ± 8.4° vs MRI: 18.2° ± 6.6°, P < 0.001), Cervical tilt (DTS: 16.4° ± 5.6° vs MRI: 11.9° ± 6.5°, P < 0.001), and cranial tilt (DTS: 9.8° ± 9.3° vs MRI: 6.6° ± 8.3°, P = 0.015). Strong correlations existed for O-C2 (r = 0.834, P < 0.001), CL (r = 0.870, P < 0.001), and T1S (r = 0.875, P < 0.001).

Conclusions

DTS reliably quantifies standing cervical alignment, particularly for cervicothoracic junction (CTJ) parameters obscured on radiography. Positional variations between standing and supine postures significantly impact cervical sagittal alignment. O-C2, CL and T1S obtained in supine position are considered meaningful parameters for evaluating cervical alignment in standing position.

Keywords

cervical spondylotic myelopathy sagittal alignment digital tomosynthesis cervical parameters position

Introduction

Cervical spondylotic myelopathy (CSM), characterized by degenerative spinal cord compression, is frequently associated with pathological alterations in cervical sagittal alignment, including loss of lordosis and increased sagittal vertical axis (SVA)¹. Moreover, parameters such as T1 slope (T1S) and thoracic inlet angle (TIA) are critical for surgical planning and postoperative evaluation^2,3.

While standing radiography remains the gold standard for evaluating cervical sagittal alignment, its clinical application faces two major limitations: positional dependency and anatomical obscuration. First, approximately 20% of patients cannot maintain the required standing position due to neurological deficits or severe pain⁴. Second, conventional radiographs often fail to visualize the cervicothoracic junction (CTJ) adequately due to shoulder obstruction, with reported measurement inaccuracies reaching 5° in T1S assessments⁵. These constraints have prompted investigations into supine MRI/CT as alternative modalities for T1-related parameter measurement^6,7. However, supine MRI/CT, while essential for evaluating spinal cord compression, does not account for gravitational effects on cervical alignment. In addition, recent efforts to establish posture-dependent correlations through mathematical modeling have yielded inconsistent results^8–10.

To address these methodological challenges, our study introduced digital tomosynthesis (DTS) - a tomographic imaging technique combining multi-angle projections - to obtain artifact-free visualization of CTJ anatomy through shoulder obstruction elimination and investigate the difference and correlation of cervical sagittal alignment between standing and supine position, providing reliable cervical alignment assessment for non-ambulatory patients and achieve a more proper cervical fusion and fixation in cervical spinal operation.

Materials and Methods

Study Design and Participants

This was a single center study enrolling 101 consecutive CSM patients from March 2023 to November 2024. Patients meeting inclusion criteria (age >18 years, symptomatic myelopathy confirmed by MRI, no prior cervical surgery) underwent both standing DTS and supine MRI within 48 hours. Exclusion criteria included trauma, deformity, inflammatory arthritis, or active infection. Patients’ general information was collected (Table 1). Institutional review board approval and informed consent were obtained.

Table 1.

Demographic Characteristics

Characteristics	Values (n = 101)
Gender
Male	59
Female	42
Age (years)	52.6 ± 8.8
BMI	23.4 ± 2.0
Levels of compression
1	47
2	42
3	12

BMI, body mass index.

Imaging and Parameter Measurements

Standing DTS images were obtained using a clinical DTS system (SONIALVISION G4, Shimazu Co, Japan) with patients maintaining neutral gaze (Figure 1). The distance was 0.8 m between the X-ray tube and flat panel detector with 100 kV and 45 mAs for shotting. Sixty frames of DTS images were reconstructed, and the central sagittal slice was chosen for measurement. Supine MRI scans were performed using a 1.5 T scanner (Magnetom Avanto, Siemens Medicals Solutions, Erlangen, Germany) with neutral head position. T2-weighted midsagittal imaging was chosen for measurement.

Figure 1.

Schematic diagram of DTS image shooting

O-C2 is defined as the angle between the McGregor’s line and the lower endplate of C2. CL is defined as the angle between the lower endplates of C2 and C7. C2-7 SVA is defined as the horizontal distance from the centroid of C2 to posterosuperior corner of C7. NT is defined as the angle between the vertical line passing through the upper end of sternum and a line connecting the midpoint of the upper endplate of T1 (T1UEP) and the upper end of sternum. T1S is defined as the angle between T1UEP and the horizontal line. TIA is defined as the angle between the line perpendicular to T1UEP and passing through the midpoint of T1UEP and the line connecting the midpoint of the T1UEP and the upper end of sternum. Cervical tilt is defined as the angle formed between the perpendicular line to T1UEP and the line from the midpoint of T1UEP to the tip of the dens. Cranial tilt is defined as the angle formed between the line from the midpoint of T1UEP to the tip of the dens and the plumb line (Figure 2). (T1S = Cervical tilt + Cranial tilt). For the values of O-C2 and CL, lordosis is considered negative and kyphosis is considered positive.

Figure 2.

The cervical sagittal parameters are measured on both MRI (A, B) and DTS images (C, D)

Two independent spine surgeons blinded to clinical data measured parameters using Picture Archiving and Communication System (PACS), and values agreed by both readers was recorded, and the average of two measurements was used for data analysis.

Statistical Analysis

All collected data were analyzed using SPSS Statistics, version 22.0. (IBM Corp., Armonk, NY, USA). Continuous variables were presented as mean ± SD, and the normal distribution was assessed by Kolmogorov-Smirnov test. The inter-rater reliability of parameter measurement was evaluated using inter-class correlation coefficient (ICC), with the grading as follows: 0.8-1.0, excellent; 0.6-0.8, good; 0.4-0.6, moderate; and <0.4, poor. Paired t-test was used to compare the parameters measured on DTS and MRI. Correlation analysis was conducted by Pearson correlation. The P values less than 0.05 were considered statistically significant. The grade of r is as follows: −1.0 to −0.5 or 0.5 to 1.0, strong; −0.5 to −0.3 or 0.3 to 0.5, moderate; −0.3 to −0.1 or 0.1 to 0.3, weak; and −0.1 to 0.1, none or very weak.

Results

Demographics

Fifty-nine males (58.4%) and 42 females (41.6%) were included in this study with a mean age of 52.6 ± 8.8 years (range from 34 to 77 years) and a mean Body Mass Index (BMI) of 23.4 ± 2.0 kg/m² (range from 18.8 to 27.3 kg/m²). The number of single, double and 3 levels of compression were 47, 42, and 12, respectively.

Reliability Analysis

The ICC values of O-C2, CL, C2-7 SVA, TIA, T1S, NT, cervical tilt, and cranial tilt measured on DTS were 0.897, 0.917, 0.885, 0.903, 0.943, 0.918, 0.913, 0.866, respectively. The ICC values of O-C2, CL, C2-7 SVA, TIA, T1S, NT, cervical tilt, and cranial tilt measured on MRI were 0.869, 0.899, 0.910, 0.894, 0.933, 0.860, 0.885, 0.871, respectively. All parameters demonstrated excellent interobserver agreement (P < 0.001) (Table 2).

Table 2.

The Outcome of Inter-rater Reliability of Parameter Measurement

Parameters	ICC	P	Level of agreement
O-C2
DTS	0.897	<0.001	Excellent
MRI	0.869	<0.001	Excellent
CL
DTS	0.917	<0.001	Excellent
MRI	0.899	<0.001	Excellent
C2-7 SVA
DTS	0.885	<0.001	Excellent
MRI	0.910	<0.001	Excellent
TIA
DTS	0.903	<0.001	Excellent
MRI	0.894	<0.001	Excellent
T1S
DTS	0.943	<0.001	Excellent
MRI	0.933	<0.001	Excellent
NT
DTS	0.918	<0.001	Excellent
MRI	0.860	<0.001	Excellent
Cervical tilt
DTS	0.913	<0.001	Excellent
MRI	0.885	<0.001	Excellent
Cranial tilt
DTS	0.866	<0.001	Excellent
MRI	0.871	<0.001	Excellent

ICC, intraclass correlation coefficients; O-C2, O-C2 angle; CL, cervical lordosis; C2-7 SVA, C2-7 sagittal vertical axis; TIA, thoracic inlet angle; T1S, T1 slope, NT, neck tilt, DTS, digital tomosynthesis; MRI, magnetic resonance imaging.

Differences and Correlation Analysis of Parameters

No significant difference was observed in TIA (DTS: 75.4° ± 16.5° vs. MRI: 71.7° ± 15.1°, P > 0.05) and NT (DTS: 49.1° ± 18.7° vs. MRI: 53.3° ± 15.7°, P > 0.05) Significant statistical difference was observed in O-C2 (DTS: -24.2° ± 11.2° vs. MRI: -14.3° ± 6.6°, P < 0.001), CL (DTS: −15.2° ± 4.4° vs. MRI: -8.1° ± 3.6°, P < 0.001), C2-7 SVA (DTS: 23.6 ± 11.0 mm vs. MRI: 16.5 ± 8.5 mm, P < 0.001), T1S (DTS: 26.3° ± 8.4° vs. MRI: 18.2° ± 6.6°, P < 0.001), cervical tilt (DTS: 16.4° ± 5.6° vs. MRI: 11.9° ± 6.5°, P < 0.001), and cranial tilt (DTS: 9.8° ± 9.3° vs. MRI: 6.6° ± 8.3°, P = 0.015). Strong correlations existed for O-C2 (r = 0.834 P < 0.001), CL (r = 0.870, P < 0.001), and T1S (r = 0.875, P < 0.001) (Table 3) (Figure 3).

Table 3.

Difference and Correlation of Parameters Measured on DTS and MRI

Variables	DTS	MRI	t	P ^a	r	P ^b
O-C2 (°)	−24.2 ± 11.2	−14.3 ± 6.6	−14.887	0.000	0.834	0.000
CL (°)	−15.2 ± 4.4	−8.1 ± 3.6	−32.849	0.000	0.870	0.000
C2-7 SVA (mm)	23.6 ± 11.0	16.5 ± 8.5	4.718	0.000	−0.193	0.054
TIA (°)	75.4 ± 16.5	71.7 ± 15.1	1.812	0.073	0.201	0.044
T1S (°)	26.3 ± 8.4	18.2 ± 6.6	19.671	0.000	0.875	0.000
NT (°)	49.1 ± 18.7	53.3 ± 15.7	−1.840	0.069	0.127	0.205
Cervical tilt (°)	16.4 ± 5.6	11.9 ± 6.5	5.027	0.000	−0.115	0.254
Cranial tilt (°)	9.8 ± 9.3	6.6 ± 8.3	2.473	0.015	−0.147	0.141

^aPaired t test.

^bPearson correlation.

Figure 3.

The correlations of key cervical sagittal parameters on MRI and DTS images

Discussion

Although DTS is not the latest technology, there is limited research on its application in cervical alignment assessment. Our previous study utilizing DTS evaluated differences in cervical sagittal parameters between asymptomatic individuals and patients with CSM in the standing position, which lays the foundation for subsequent related research¹¹. The present study constitutes the first comprehensive investigation comparing cervical sagittal alignment parameters between weight-bearing standing DTS and supine MRI in CSM patients. Our findings demonstrate 3 critical clinical insights: (1) DTS provides reliable visualization and quantification of CTJ parameters that are frequently obscured in conventional radiography; (2) postural changes from standing to supine position induce significant alterations in most cervical alignment parameters; and (3) strong correlations exist between supine MRI-derived and standing DTS-derived measurements for O-C2 angle, CL, and T1S, suggesting these parameters maintain consistent inter-postural relationships despite positional variations. These findings advance our understanding of cervical biomechanics across postures and provide practical guidance for surgical planning in non-ambulatory patients.

DTS as a Superior Modality for CTJ Assessment

The technical superiority of DTS in visualizing CTJ anatomy resolves a long-standing limitation of conventional radiography. Traditional methods for measuring T1S and related parameters have been plagued by a 23-47% rate of inadequate visualization due to shoulder superimposition, leading to measurement errors exceeding 5° in T1S assessments^12–14. Our data corroborate previous reports that DTS effectively eliminates anatomical overlap through tomographic reconstruction¹⁵, evidenced by excellent inter-rater reliability (ICC >0.9) for all CTJ parameters. This technical advantage is particularly crucial for surgical planning, as T1S and TIA have been established as key determinants of postoperative alignment compensation and adjacent segment degeneration^2,16,17. The ability to accurately measure these parameters in standing position addresses a critical gap in preoperative evaluation, enabling surgeons to better predict cervical balance restoration and construct durability.

Posture-Dependent Cervical Alignment Dynamics

Our findings reveal profound postural effects on cervical alignment, with standing DTS demonstrating significantly greater cervical lordosis (−15.2° vs. −8.1°), O-C2 angle (−24.2° vs. −14.3°), and T1S (26.3° vs. 18.2°) compared to supine MRI. These differences likely reflect the combined effects of gravitational loading, muscular tone modulation, and postural compensation mechanisms. The increased cervical lordosis in standing position aligns with the “column hypothesis” of spinal stability, where increased axial loading promotes segmental coupling to maintain horizontal gaze¹⁸. The marked reduction in C2-7 SVA from 23.6 mm (standing) to 16.5 mm (supine) suggests gravitational forces induce anterior translation of the cervical mass, potentially exacerbating degenerative changes in weight-bearing positions—a phenomenon that may explain symptom variation between upright and recumbent states in CSM patients.

Notably, TIA and NT showed no significant postural variation (P > 0.05), consistent with their anatomical nature as fixed skeletal parameters^19,20. This stability reinforces their utility as foundational references for surgical planning, as they remain unaffected by transient postural adjustments. The strong correlation between standing and supine T1S (r = 0.875) further supports the concept that while T1S magnitude changes with posture, its inherent relationship to other parameters persists²¹. This finding challenges earlier assumptions that supine T1S measurements lack clinical relevance, instead suggesting they retain predictive value for standing alignment when combined with compensatory mechanisms.

Clinical Implications for Non-ambulatory Patients

The strong correlations between supine MRI and standing DTS measurements for O-C2 (r = 0.834), CL (r = 0.870), and T1S (r = 0.875) provide a scientific basis for estimating weight-bearing alignment in patients unable to maintain standing positions. This is particularly relevant given that a considerable number of CSM patients cannot undergo standard radiography due to neurological deficits²². Our data suggest supine MRI measurements of these 3 parameters could serve as reliable proxies for standing alignment, enabling surgeons to approximate physiological spinal balance even when upright imaging is unattainable.

However, caution must be exercised with C2-7 SVA, which showed no significant correlation (r = -0.193) between two postures. The 7.1 mm mean difference (23.6 mm vs. 16.5 mm) indicates that supine MRI substantially underestimates sagittal imbalance, potentially leading to inadequate correction if used in isolation. This aligns with biomechanical studies showing SVA is highly sensitive to postural muscle deactivation in recumbent positions^23,24. Therefore, surgical strategies based solely on supine SVA measurements risk creating iatrogenic hyperlordosis when the patient resumes upright posture.

Limitations

This study has several limitations. First, the single-center design and exclusion of non-degenerative pathologies may limit generalizability. Second, the 48-hour interval between DTS and MRI introduces potential confounding from transient postural adaptations, though this reflects real-world clinical workflows. Third, the lack of healthy controls prevents differentiation between pathological and physiological postural changes. Future studies incorporating longitudinal follow-up could clarify whether the observed correlations persist postoperatively.

Conclusions

This study establishes DTS as a reliable alternative to conventional radiography for assessing weight-bearing cervical alignment, particularly in visualizing CTJ parameters critical for surgical planning. The strong O-C2, CL, and T1S correlations between modalities provide a bridge for evaluating non-ambulatory patients, enabling more accurate surgical planning when upright imaging is unfeasible. These findings advance our ability to personalize CSM management across the spectrum of patient mobility.

Footnotes

ORCID iDs

Shengbiao Ma

Peng Zhang

Ethical Considerations

The study was conducted according to the guidelines of the Declaration of Helsinki and approved by the institutional review board of the authors’ affiliated institutions (2021042).

Consent to Participate

The ethical committee waived the need for informed consent as it was a retrospective study.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study was supported by Scientific Research Startup Fund of Henan Cancer Hospital (No. zx2156) and Henan Provincial Science and Technology Research Project (No. 252102311199).

Declaration of Conflicting Interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Data Availability Statement

The datasets used or analyzed during the current study are available from the corresponding author on reasonable request.*

References

Yoshida

Alzakri

Pointillart

, et al. Global spinal alignment in patients with cervical spondylotic myelopathy. Spine. 2018;43(3):E154-E162. doi:10.1097/BRS.0000000000002253

Kenta

Eiji

Tokue

, et al. Usefulness of the preoperative thoracic inlet angle in comparison to the T1 slope for predicting cervical kyphosis after laminoplasty. Eur Spine J. 2024;33(3):1179-1186. doi:10.1007/s00586-023-08095-4

Iyer

Nemani

Nguyen

, et al. Impact of cervical sagittal alignment parameters on neck disability. Spine. 2016;41(5):371-377. doi:10.1097/brs.0000000000001221

Mizoguchi

Akasaka

Suzuki

Kimura

Hall

Ogihara

. Psychometric evaluation of the Japanese neck disability index by exploratory factor analysis in preoperative patients with cervical spondylotic myelopathy: impact of pain and numbness. Spine J. 2024;24(11):2172-2180. doi:10.1016/j.spinee.2024.06.001

Tamai

Buser

Paholpak

Sessumpun

Nakamura

Wang

. Can C7 slope substitute the T1 slope? an analysis using cervical radiographs and kinematic MRIs. Spine. 2018;43(7):520-525. doi:10.1097/BRS.0000000000002371

Noh

Lee

, et al. Diagnostic accuracy of magnetic resonance imaging for sagittal cervical spine alignment: a retrospective cohort study. Int J Environ Res Publ Health. 2021;18(24):13033. doi:10.3390/ijerph182413033

Bae

Son

Lee

Song

. Can supine magnetic resonance imaging be an alternative to standing lateral radiographs for evaluating cervical sagittal alignment? Korean J Nutr. 2020;16(2):226-234. doi:10.13004/kjnt.2020.16.e18

Karabag

Iplikcioglu

. Simulating upright cervical lordosis in the supine position. Acta Orthop Belg. 2022;88(2):293-301. doi:10.52628/88.2.8987

Shen

. Comparison of cervical sagittal parameters between radiographs and magnetic resonance images in patients with cervical spondylotic myelopathy. Glob Spine J. 2023;13(7):1932-1937. doi:10.1177/21925682211062498

10.

Oshina

Tanaka

Oshima

Tanaka

Riew

. Correlation and differences in cervical sagittal alignment parameters between cervical radiographs and magnetic resonance images. Eur Spine J. 2018;27(6):1408-1415. doi:10.1007/s00586-018-5550-z

11.

Ding

Zhou

Wang

Tang

Zhang

. Digital tomosynthesis enhances cervicothoracic sagittal alignment assessment: are cervicothoracic sagittal parameters correlated with the occurrence of cervical spondylotic myelopathy? Eur Spine J. 2025;37(8):3262-3270. doi:10.1007/s00586-025-09074-7

12.

Qiao

Zhu

Liu

, et al. Measurement of thoracic inlet alignment on MRI: reliability and the influence of body position. Clin Spine Surg. 2017;30(4):E377-E380. doi:10.1097/BSD.0000000000000306

13.

Lee

Jeon

Chung

Kwon

. Comparative analysis of three imaging modalities for evaluation of cervical sagittal alignment parameters: a validity and reliability study. Spine. 2017;42(24):1901-1907. doi:10.1097/BRS.0000000000002256

14.

Nakashima

Matsumoto

Ito

, et al. Impact of T1 slope visibility on cervical sagittal alignment: a comparative study of radiographic parameters according to T1 slope visibility. Spine Surg Relat Res. 2025;9(3):307-312. doi:10.22603/ssrr.2024-0253

15.

Blum

Noel

Regent

Villani

Gillet

Gondim Teixeira

. Tomosynthesis in musculoskeletal pathology. Diagn Interv Imaging. 2018;99(7-8):423-441. doi:10.1016/j.diii.2018.05.001

16.

Scheer

Tang

Smith

, et al. Cervical spine alignment, sagittal deformity, and clinical implications: a review. J Neurosurg Spine. 2013;19(2):141-159. doi:10.3171/2013.4.Spine12838

17.

Hyun

Kim

Jahng

. The differential effect of cervical kyphosis correction surgery on global sagittal alignment and health-related quality of life according to head- and trunk-balanced subtype. J Neurosurg Spine. 2021;34(6):839-848. doi:10.3171/2020.9.Spine201309

18.

Karabag

Iplikcioglu

. Normative ranges of horizontal gaze parameters and their correlations with cervical sagittal parameters. Orthop Traumatol Surg Res. 2025;104305. doi:10.1016/j.otsr.2025.104305

19.

Cheng

Liu

Sun

, et al. Correlation of cervical and thoracic inlet sagittal parameters by MRI and radiography in patients with cervical spondylosis. Medicine (Baltim). 2019;98(7):e14393. doi:10.1097/md.0000000000014393

20.

Xing

Liu

Jiang

Yishakea

Dong

. Characteristics of cervical sagittal parameters in healthy cervical spine adults and patients with cervical disc degeneration. BMC Muscoskelet Disord. 2018;19(1):37. doi:10.1186/s12891-018-1951-8

21.

Kong

Sun

, et al. The ratio of C2-C7 cobb angle to T1 slope is an effective parameter for the selection of posterior surgical approach for patients with multisegmental cervical spondylotic myelopathy. J Orthop Sci. 2020;25(6):953-959. doi:10.1016/j.jos.2019.12.008

22.

Park

Lee

. Choosing the right treatment for degenerative cervical myelopathy. J Clin Orthop Trauma. 2025;66:103014. doi:10.1016/j.jcot.2025.103014

23.

Lin

Wang

Chen

Liu

. Is cervical sagittal balance related to the progression of patients with cervical spondylotic myelopathy? World Neurosurg. 2020;137:e52-e67. doi:10.1016/j.wneu.2019.12.148

24.

Goldschmidt

Angriman

Agarwal

, et al. A new piece of the puzzle to understand cervical sagittal alignment: utilizing a novel angle Delta to describe the relationship among T1 vertebral body slope, cervical lordosis, and cervical sagittal alignment. Neurosurgery. 2020;86(3):446-451. doi:10.1093/neuros/nyz088