Abstract
Study Design
A cross-sectional retrospective study.
Objectives
This study aims to analyze the correlation between cervical disc degeneration grade and cervical imaging parameters and improve grade assessment objectivity and accuracy under the Miyazaki disc degeneration grading system.
Methods
Cervical disc degeneration was graded using the Miyazaki disc degeneration grading system. Cervical imaging parameters included the disc height index (DHI) and segmental range of motion (sROM) in the lateral X-ray view. Correlation, subgroup analysis, and linear regression analysis were conducted to analyze the relationships between cervical disc degeneration grades, DHI, and sROM, respectively. The kappa value for the Miyazaki disc degeneration grading system was analyzed before and after considering imaging parameters.
Results
A total of 98 patients (47 males and 51 females, age from 29 to 85 years ) with 490 discs were included in the analysis. Correlation analysis revealed that cervical disc degeneration grade related to DHI (ρ = −0.543, P < 0.001) and sROM (ρ = −0.309, P < 0.001) across different cervical segments, age, sex, and body mass index groups (majority of P < 0.05). Linear regression analysis illustrated a negative impact of the cervical disc degeneration grade on DHI (B = −0.058, P < 0.001) and sROM (B = −0.903, P < 0.001). Regarding the regression coefficients, the kappa value for the Miyazaki disc degeneration grading system increased from 0.626 to 0.812.
Conclusions
Cervical disc degeneration grade was associated with DHI and sROM in adult patients, and reference to cervical imaging parameters could improve the objectivity and accuracy of the Miyazaki disc degeneration grading system.
Keywords: cervical disc degeneration grade, disc height index, segmental range of motion
Introduction
Cervical disc degenerative disease is a group of diseases related to cervical intervertebral disc degeneration, which includes disc herniation, cervical misalignment, instability, and others. 1 These structural and functional changes often cause compression on the nerve roots or spinal cord, neck and shoulder pain, limb numbness and weakness, and even paralysis. Cervical disc degeneration involves water and proteoglycan loss, altering the shape and mechanical properties of the disc, which further leads to changes in anatomic parameters and functional activities.2,3
Assessing cervical disc degeneration is useful in diagnosing and treating cervical disc degenerative diseases. The current assessment is commonly based on the Miyazaki disc degeneration grading system using magnetic resonance imaging (MRI).4,5 The grading system includes five degeneration grades, with a higher grade indicating a greater degree of degeneration. The reference criteria of the grading system include the nucleus signal intensity and structure, the distinction between the nucleus and annulus, and disc height. Most components in the grading system analyze annulus fibrosus and nucleus pulposus signals in MRI, while classifying the signals into different grade groups is dependent on the doctors’ visual judgment and their clinical experience, which causes much error among different doctors and even in the same doctor at different time.5,6 Much error in the grade assessment usually indicate significant subjectivity and variability in the assessment results. Some studies applied the Pfirrman classification, originally used for lumbar disc degeneration, to cervical disc degeneration, which also brought much subjectivity and variability to observers.7-9 A new grading system developed by Jacobs et al classified cervical disc degeneration based on disc signal intensity and height and osteophytes or not through visual observation, which is still hard to reduce the error. 5
Imaging data are mainly obtained from measurements and can often largely reduce the subjectivity and variability of grade assessment results, indicating that grading system association with objective imaging parameters may reduce error in clinical application.
As cervical disc degeneration progresses, cervical disc height and segmental range of motion (sROM) tend to decrease, whereas segmental translational motion (sTM) initially increases and then decreases.10,11 Additionally, in correlation with the progression of cervical disc degeneration, these three parameters are readily measurable in clinical practice, and the corresponding data are objective. These features aligned well with the imaging parameters, which may be linked to the cervical disc degeneration grading system. Consequently, this study aimed to analyze the correlation between cervical disc degeneration grade and cervical disc height, sROM, and sTM, which may provide a quantitative reference for evaluating cervical degeneration grade and aid in improving the objectivity and accuracy of grade assessments under the Miyazaki disc degeneration grading system.
Methods
After approval from the ethics committee of our hospital (approval number: K-2025-040), a cross-sectional retrospective study was conducted in which data were consecutively obtained from patients with symptomatic neck pain or with/without radiculopathy or myelopathy between October 1, 2023, and September 30, 2024, in the spinal surgery department of a tertiary teaching hospital.
The inclusion criteria were as follows: (1) Age over 18 years, (2) availability of clear cervical spine MRI images and both static and dynamic cervical X-ray sagittal images that were obtained at the same visit as the MRI examination. Patients with one or more of the following criteria were excluded: (1) History of cervical spine surgery, (2) history of cervical spine fracture due to trauma or other causes, (3) presence of cervical spine infection, tumors, or congenital scoliosis.
Cervical disc degeneration was graded using the Miyazaki disc degeneration grading system (Figure 1). 10 T2-weighted midsagittal MRI (Philips Co, Achieva 3.0 Quasar Dual 3.0T-MRI) images of C2–C7 were selected for assessing cervical disc degeneration in a blinded fashion. Each MRI image was independently evaluated by two spinal attending surgeons (each surgeon has over five years of experience). In cases of disagreement, a senior spinal surgeon who did not participate in any other aspect of the study acted as adjudicator. The weighted kappa value, interobserver agreement, and disagreement were assessed (the kappa value is deemed suitable for assessing interobserver reliability. A kappa value less than 0.20 suggests poor agreement, value from 0.20 to 0.40 indicates general agreement, value from 0.40 to 0.60 represents moderate agreement, value from 0.60 to 0.80 denotes good agreement, and value greater than 0.80 reflects excellent agreement). 12
Figure 1.
Miyazaki Disc Degeneration Grading System for Cervical Disc degeneration. (A): Grade I of Cervical Disc degeneration, (B): Grade II of Cervical Disc degeneration, (C): Grade III of Cervical Disc degeneration, (D): Grade IV of Cervical Disc degeneration, (E): Grade V of Cervical Disc Degeneration
Imaging data included cervical disc height index (DHI), which could reflect the information of intervertebral height more comprehensively, cervical sROM, and sTM of C2-C7, which were measured on cervical lateral neutral, maximal flexion, and maximal extension X-rays images using Surgimap software (version 2.3.2.1). DHI measurement: In the cervical lateral neutral X-ray view, a crossing point of two diagonal lines of each vertebral body was created as the vertebral center, and the midvertebral line was drawn by connecting the two adjacent vertebral centers. The heights of the disc (a) and the vertebral body (b) were determined using the midvertebral line. DHI was defined as a/b (Figure 2A). 13 sROM measurement: Flexion-extension X-ray images were used to measure the segmental angle of each cervical disc in maximal flexion and extension positions, respectively (Figure 2B, and C). The difference between maximal flexion segmental angle and maximal extension segmental angle was defined as sROM (sROM = ∠β-∠α). 14 sTM was defined as the anterioposterior motion distance of upper vertebra over lower under maximal flexion and extension (sTM = d2-d1), and a positive value meant anterior translation while a negative value meant posterior translation (Figure 2B, and C). 15 Meanwhile, general data, including age, sex, and body mass index (BMI), were collected.
Figure 2.
Schematic Measurements for Cervical Imaging Parameters in Lateral X-Rays. (A): Disc Height Index = a/b; (B)-(C): Segmental Range of Motion = ∠β-∠α, Segmental Translation Motion = d2-d1
Data analysis was performed using the IBM SPSS software (version 26.0). Continuous data are presented as mean ± standard deviation for normally distributed data. Spearman correlation test was used to evaluate the relationships between cervical disc degeneration grade, DHI, sROM, and sTM, respectively, and to further analyze the relationships under different cervical segments, age, sex, and BMI groups. Linear regression analysis was used to quantitatively analyze how changes in DHI and sROM values were affected by changes in cervical disc degeneration grade. One-way analysis of variance (ANOVA) was used to analyze whether there were differences in DHI and sROM among different segments under the same cervical disc degeneration grade. Statistical significance was set at P < 0.05 (two-sided).
To assess whether weighted kappa value, interobserver agreement improved or not after referring to imaging parameter (DHI and sROM), the same MRI images were independently re-evaluated by two other spinal attending surgeons with the same experience as previous surgeons. The weighted kappa value, interobserver agreement, and disagreement before and after referring to the imaging parameters were then compared.
Results
Characteristics of Patients
The study included 98 patients, among which 47 were male and 51 were female, with ages ranging from 29 to 85 years [mean ± standard deviation: 57.8 ± 11.4 years] and BMI being 24.2 ± 2.8 kg/m2. A total of 490 discs were included and further divided into 5 grades following the Miyazaki disc degeneration grading system: Grade I: 41 (8.4%); grade II: 80 (16.3%); grade III: 175 (35.7%); grade IV: 138 (28.2%); grade V: 56 (11.4%) (Table 1).
Table 1.
Patients’ Demographic Characteristics
| Characteristic | No. Of patients (N = 98 patients) |
|---|---|
| Age (years), mean ± SD | 57.8 ± 11.4 |
| Sex, n (%) | |
| Male | 47 (48.0%) |
| Female | 51 (52.0%) |
| BMI (kg/m2), mean ± SD | 24.2 ± 2.8 |
| Disc degeneration grade, n (%) | |
| I | 41 (8.4%) |
| II | 80 (16.3%) |
| III | 175 (35.7%) |
| IV | 138 (28.2%) |
| V | 56 (11.4%) |
SD: standard deviation, BMI: body mass index.
Correlation Analysis Between Cervical Disc Degeneration Grade, DHI, sROM, and sTM
Spearman correlation analysis revealed that the cervical disc degeneration grade was significantly and negatively correlated with both DHI (ρ = −0.543, P < 0.001) and sROM (ρ = −0.309, P < 0.001); however, no significant trend of first increase and then decrease was found between the grade and sTM (grade I to III: ρ = 0.046, P = 0.43; grade III to V: ρ = −0.107, P = 0.07) (Figure 3).
Figure 3.
Correlation Between Cervical Disc Degeneration Grade and DHI, sROM, and sTM
Subgroup analysis between degeneration grade, DHI and sROM was conducted according to different cervical segments, age, sex, and BMI.
In the subgroup analysis of the different cervical segment groups, both DHI and sROM decreased to a varying extent as the degeneration grade increased in all segments. Meanwhile, DHI and sROM in C2/3 were generally smaller than those in C3/4, C4/5, C5/6, and C6/7 (all P < 0.01, but P = 0.07 for the correlation of sROM and degeneration under C2/3) (Figure 4).
Figure 4.
Correlation Between Cervical Disc Degeneration Grade and DHI, sROM Under Different Cervical Segments
Subgroup analysis according to sex exhibited a negative correlation between the degeneration grade, DHI and sROM in both male and female patients (all P < 0.001) (Figure 5). Meanwhile, subgroup analysis of different age groups (18-45 years of 13 patients, 46-55 years of 29 patients, 56-65 years of 29 patients, and 66+ years of 27 patients) indicated that four age groups represented a negative correlation between the degeneration grade, DHI and sROM, respectively (all P < 0.001) (Figure 5). Similarly, subgroup analysis of different BMI groups (18.5-24.0 kg/m2 of 53 patients, 24.0-28.0 kg/m2 of 39 patients, 28.0+ kg/m2 of 6 patients) exhibited a significantly negative correlation between degeneration grade, DHI, and sROM, respectively, for the first two groups (all P < 0.001); however, no significant correlation was observed in patients with BMI ≥28.0 kg/m2 (correlation for grade and DHI, sROM, respectively: ρ = −0.352, P = 0.06, and ρ = −0.083, P = 0.66) (Figure 5).
Figure 5.
Correlation Between Cervical Disc Degeneration Grade and DHI, sROM Under Different Age, Sex, and BMI Groups
Linear Regression Analysis of Cervical Disc Degeneration Grade, DHI, and sROM, Respectively
Linear regression analysis exhibited a negative impact of cervical disc degeneration grade on DHI (B = −0.058, P < 0.001) and sROM (B = −0.903, P < 0.001), suggesting that one-unit increase in the degeneration grade, DHI decreased by 0.058 units, and sROM decreased by 0.903° (Table 2).
Table 2.
Results of Linear Regression Analysis of Cervical Disc Degeneration Grade and DHI, sROM, Respectively
| Model | Unstandardized coefficients | Standardized coefficients | t | P value | Confidence interval for B | |||
|---|---|---|---|---|---|---|---|---|
| B | Standard error | Beta | CI (2.5%) | CI (97.5%) | ||||
| 1 DHI |
Constant | 0.535 | 0.013 | 41.524 | <0.001 | 0.510 | 0.561 | |
| Degeneration grade | −0.058 | 0.004 | −0.562 | −15.007 | <0.001 | −0.065 | −0.050 | |
| 2 sROM | Constant | 8.994 | 0.426 | 21.105 | <0.001 | 8.157 | 9.832 | |
| Degeneration grade | −0.903 | 0.127 | −0.307 | −7.123 | <0.001 | −1.151 | −0.654 | |
One-Way Analysis of Variance of DHI and sROM, Respectively, in Different Cervical Disc Degeneration Grades
The results of ANOVA based on Table 3 illustrated that the majority of DHI in C3-C7 under grades I to IV were larger than those in C2/3, and parts of sROM in C3-C7 under grades I to III were larger than those in C2/3, while sROM of C5/6 was smaller than that in C4/5 (P < 0.05). No significant differences were found in other pairwise comparisons.
Table 3.
Values of DHI and sROM in Different Cervical Disc Degeneration Grades
| N | Grade I | N | Grade II | N | Grade III | N | Grade IV | N | Grade V | ||
|---|---|---|---|---|---|---|---|---|---|---|---|
| DHI | C2/3 | 8 | 0.343 ± 0.034 | 14 | 0.308 ±0.076 | 24 | 0.232 ± 0.045 | 45 | 0.251 ± 0.053 | 7 | 0.136 ± 0.106 |
| C3/4 | 9 | 0.528 ± 0.050*** | 25 | 0.414 ± 0.062** | 43 | 0.402 ± 0.084*** | 16 | 0.330 ± 0.065** | 5 | 0.216 ± 0.079 | |
| C4/5 | 11 | 0.434 ± 0.106 | 18 | 0.391 ± 0.095 | 40 | 0.357 ± 0.080*** | 18 | 0.319 ± 0.080* | 11 | 0.264 ± 0.161 | |
| C5/6 | 7 | 0.535 ± 0.065* | 7 | 0.445 ± 0.070* | 32 | 0.383 ± 0.071*** | 27 | 0.308 ± 0.061** | 25 | 0.292 ± 0.114 | |
| C6/7 | 6 | 0.484 ± 0.109 | 16 | 0.445 ± 0.074*** | 36 | 0.387 ± 0.096*** | 32 | 0.301 ± 0.080* | 8 | 0.256 ± 0.117 | |
| sROM | C2/3 | 8 | 5.700 ± 1.654 | 14 | 4.886 ± 2.544 | 24 | 4.921 ± 2.098 | 45 | 4.584 ± 2.291 | 7 | 3.257 ± 3.357 |
| C3/4 | 9 | 8.033 ± 1.730 | 25 | 7.604 ± 2.490* | 43 | 7.302 ± 2.954** | 16 | 6.181 ± 3.709 | 5 | 4.120 ± 4.972 | |
| C4/5 | 11 | 9.327 ± 2.752* | 18 | 7.667 ± 3.640 | 40 | 8.323 ± 3.554*** | 18 | 5.956 ± 2.829 | 11 | 6.073 ± 3.832 | |
| C5/6 | 7 | 8.143 ± 3.840 | 7 | 6.900 ± 5.434 | 32 | 5.750 ± 2.611 a | 27 | 4.985 ± 2.809 | 25 | 4.476 ± 2.935 | |
| C6/7 | 6 | 7.567 ± 3.830 | 16 | 6.725 ± 2.853 | 36 | 6.283 ± 3.228 | 32 | 4.678 ± 2.358 | 8 | 3.975 ± 2.850 |
*: P < 0.05, **: P < 0.01, ***: P < 0.001, these * symbols all indicate that the DHI and sROM values of related C3/4, C4/5, C5/6, and C6/7 are higher than those in C2/3 significantly in the same grade.
P < 0.05.
asROM of C5/6 vs sROM of C4/5.
Kappa Values, Interobserver Agreement and Disagreement
In the period of assessment without references to DHI and sROM, the kappa value was 0.626, and the agreement was 54.6%, while the kappa value and agreement were 0.810 and 78.0% in the period of assessment with references to DHI and sROM. Compared to the disagreement in the first period, disagreement in grade I to IV of the other period decreased, with the greatest reduction of 12.1% in grade III, while disagreement in grade V increased slightly (Table 4).
Table 4.
Comparison of Kappa Value, Interobserver Agreement and Disagreement Before and After Consideration of DHI or sROM
| With DHI and sROM or not | Kappa | Agreement | Disagreement | ||||
|---|---|---|---|---|---|---|---|
| Grade I | Grade II | Grade III | Grade IV | Grade V | |||
| Without | 0.626 | 268 (54.6%) | 33 (6.7%) | 13 (2.7%) | 119 (24.3%) | 42 (8.6%) | 15 (3.1%) |
| With | 0.810 | 382 (78.0%) | 5 (1.0%) | 10 (2.0%) | 60 (12.2%) | 16 (3.3%) | 17 (3.5%) |
Discussion
The assessment of cervical disc degeneration is dependent on the grading system, with the Miyazaki disc degeneration grading system specifically used for cervical disc. Certain subjectivity has been found when applying the grading system, which causes much error in clinical practice.5,6 The involvement of imaging parameters perhaps could reduce the error to a varying extent and increase the accuracy and reliability of grade assessment.
Following the correlation analysis, there was a strong negative correlation (ρ = −0.543, P < 0.001) and a moderate negative correlation (ρ = −0.309, P < 0.001) between cervical disc degeneration grade, DHI, and sROM, respectively, indicating DHI and sROM decrease along with increased cervical disc degeneration grade. An increase in degeneration grade means aggravation of cervical disc degeneration. Such relevance indicates that deterioration of cervical disc degeneration is related to the decrease of DHI and sROM, which corresponds to the occurrence of less disc height and mobility caused by cervical disc degeneration. 16 The absence of a clear correlation between initial increase and subsequent decrease for the sTM may be linked to the lack of C7-T1 and only a small number of cervical discs with grade V having intervertebral osteophytes or fusion (11 out of 56 cervical discs). 4 Further subgroup analysis revealed that the significant negative correlations between the degeneration grade, and DHI, sROM still exist under different cervical segments (except for the group of C2/3 in sROM analysis), age, sex, and BMI (except for the group with BMI ≥28.0 kg/m2 in sROM analysis). Despite the small sample size in patients with BMI ≥28.0 kg/m2, obese patients tend to have excess fat in their cervical region, which creates a fat pad limiting cervical mobility, 17 and mobility reduction caused by cervical disc degeneration may not be obvious.
In the linear regression analysis, one-unit increase in the cervical disc degeneration grade (independent variable) indicates DHI and sROM decreased by 0.058 units and 0.903°, respectively (dependent variable). In turn, value changes of DHI and sROM up to 0.058 units and 0.903°, respectively (or one of them), indicate one-grade change in cervical disc degeneration. In ANOVA, almost all pairwise comparisons of DHI and sROM for C3-C7 exhibited no significant differences under the same degeneration grade group, which indicated that each cervical disc degeneration grade could be evaluated as the same grade as those clearly defined grades if the differences of both DHI and sROM are within 0.058 units and 0.903°. Specifically, when one cervical disc degeneration grade was determined unequivocally but another cervical disc degeneration grade was evaluated with doubt, differences of both DHI and sROM between the two cervical discs within 0.058 units and 0.903° indicate that the cervical disc degeneration grade with doubt could be evaluated as the same grade as the clearly defined one.When DHI or sROM in one cervical disc is 0.058 units or 0.903° less than cervical disc with clearly defined degeneration grade, the cervical disc degeneration grade could be evaluated as previous better grade. On the contrary, the cervical disc degeneration grade could be assessed as next severe grade.
Smaller values of DHI and sROM of C2/3 than those in other cervical segments under the same degeneration grade were mainly determined by the higher height of the C2 vertebra and smaller mobility of C2/3. 18 Due to smaller DHI and sROM of C2/3, it would be inappropriate to evaluate degeneration grade of other segments based on C2/3 degeneration grade and the regression coefficients, and vice versa.
Much improvements in the kappa value, interobserver agreement, and disagreement occur in the period after consideration of DHI and sROM. The kappa value changed from 0.626 to 0.810, which means a good consistency to an excellent consistency and could reduce assessment error from different observers to a certain extent. 19 Besides, the improvement of 23.4% agreement was mainly from disagreement reduction in grade I (5.7%), grade III (12.1%), and grade IV (5.3%). Furthermore, the significant reduction in grades III and IV disagreement indicates that the imaging parameters reference could help reduce the assessment error of adjacent degeneration grades III and IV to some extent. Such phenomenon not only conforms to the analytical process of incorporating imaging parameters as references when grading cervical disc degeneration, but also confirms that many assessment error come from the confusion of adjacent grade of cervical disc degeneration.5,6 Improvement of objectivity and accuracy in Miyazaki disc degeneration grading system is conducive to further accurately evaluate cervical disc degeneration grade, especially for those disc grades with doubt. Accurate assessment of cervical intervertebral disc degeneration could provide some basis for decision on whether to perform surgery, the choice of surgical procedures, and prevention and treatment for postoperative complications. For example, a more severe degeneration grade represents a higher degree of disc protrusion, meaning greater probability of severe symptoms and future additional surgery, and inaccurate grade assessment may delay diagnosis and treatment of disease.11,20,21
This study has several limitations. First, the single-center, cross-sectional, and retrospective nature of the study is a potential limitation. 22 Second, adult patients with corresponding symptoms and BMI ≥18.5 kg/m2 were included in the study, which meant that minor asymptomatic or underweight people may not be applicable. Third, due to higher vertebral height and smaller C2/3 mobility, cervical disc degeneration grade assessment of C2/3 referring to DHI and sROM may cause some error. Fourth, one cervical disc degeneration grade would be evaluated poorly if other disc degeneration grades were not determined without doubt.
Conclusions
Cervical disc degeneration grade was associated with the imaging parameters of DHI and sROM in adult patients with cervical symptoms regardless of age, sex, and BMI (except for the group with BMI >28.0 kg/m2). Reference to the indicators improves the kappa value and interobserver agreement, especially reducing the assessment error from adjacent grades confusion. It can be used as an auxiliary assessment index for the Miyazaki disc degeneration grading system, which enables less subjectivity and variability in cervical disc degeneration grade assessment.
Acknowledgments
The authors sincerely thank the Home for Researchers (https://www.home-for-researchers.com/) for the language polishing and literature retrieve service.
Footnotes
Author contributions: (1) Conceptualization: Xuqiang Zhan, Zhanwei Wang, Yan Yu. (2) Data curation: Xuqiang Zhan, Zhanwei Wang, Kaiwei Wang, Abudureyimu Abudukeremu. (3) Formal analysis: Xuqiang Zhan, Zhanwei Wang, Kaiwei Wang, Ning Xie, Tao Dai, Jian Fan, Yan Yu. (4) Funding acquisition: Yan Yu. (5) Methodology: Xuqiang Zhan, Zhanwei Wang, Kaiwei Wang, Abudureyimu Abudukeremu. (6) Writing–original draft preparation: Xuqiang Zhan, Zhanwei Wang, Kaiwei Wang, Ning Xie.(7) Writing – Review & Editing: Yan Yu, Jian Fan, Tao Dai.
Funding: The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the National Natural Science Foundation of China (grant number 81873774), Shanghai Excellent Young Medical Talents Training Program (grant number 2018YQ22), Shanghai Municipal Outstanding Young Talent Support Program (grant number SKW1811), Shanghai Innovative Medical Device Application Demonstration Project (grant number 23SHS03800).
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
ORCID iDs
Kaiwei Wang https://orcid.org/0009-0001-7103-6161
Ethical Approval
This study was conducted in accordance with the Declaration of Helsinki and approved by the Tongji Hospital of Tongji University ethics committee (approval number: K-2025-040). The ethics committee approved this study and waived the requirement for informed consent because of the retrospective nature of the study.
Consent to Participate
The requirement for informed consent was waived because of the retrospective nature of this study.
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