### Introduction

### Materials and Methods

### 1. Materials

### 2. Measurements

_{1}C

_{2}Cobb angle, O

_{C}C

_{2}Cobb angle), cervical (C

_{2}C

_{7}Cobb angle, C

_{2}C

_{7}Harrison angle, O

_{C}C

_{7}Cobb angle, C

_{7}slope), thoracic (thoracic inlet angle [TIA] and TK), spinopelvic (LL, sacral slope [SS], PI, and pelvic tilt [PT]), and C

_{7}SVA. Definitions of the radiographic parameters are summarized in Table 1 [13].

*p*-value of less than 0.05 was considered significant.

### Results

### 1. Normality test

### 2. Demographic data

### 3. Descriptive results of the spinopelvic parameters

### 4. Descriptive results of the thoracic parameters

### 5. Descriptive results of the cervical and occipital parameters

_{1}C

_{2}Cobb angle was −27.07°±4.3°, O

_{C}C

_{2}Cobb angle was −14.5°±3.8°, O

_{C}C

_{7}Cobb angle was −29.8°±5.6°, C

_{2}C

_{7}Harrison angle was 20.4°±4.3°, C

_{2}C

_{7}Cobb angle was −16.4°±5.6°, and C

_{7}slope was −25.4°±5.6°. The analysis of these parameters revealed no statistically significant difference between the four groups (Table 3).

### 6. The relationship between the age and cervical spine parameters

_{2}C

_{7}Cobb angle correlated with age in the cervical group (Table 4). In the other studied groups, there was no correlation between age and cervical parameters.

### 7. The relationship between the spinopelvic and cervical spine parameters

_{7}slope and SS (

*r*=0.212,

*p*=0.039) and a negative correlation between C

_{2}C

_{7}Cobb angle and PT (

*r*=−0.2,

*p*=0.02). Also, the cervical group showed a statistically significant correlation between the C

_{1}C

_{2}Cobb angle and three spinopelvic parameters (LL:

*r*=0.2,

*p*=0.002; PI:

*r*=−0.2,

*p*=0.02; and PT:

*r*=−0.2,

*p*=0.02) (Table 4). In the post-surgical group, PI and SS were two spinopelvic parameters that showed a significant positive correlation to O

_{C}C

_{7}Cobb angle and C

_{2}C

_{7}Harrison angle (

*r*=0.2) (Table 5). Moreover, C

_{1}C

_{2}Cobb angle correlated to PT in the post-surgical group (

*r*=−0.2,

*p*=0.01). Asymptomatic subjects and the lumbar group did not show any significant correlation between the spinopelvic and cervical parameters (Tables 6, 7, Fig. 2).

_{2}C

_{7}Harrison angle and PT, C

_{2}C

_{7}Harrison angle and PI, C

_{1}C

_{2}Cobb angle and LL, and C

_{7}slope and SS. However, there was no correlation between the C

_{2}C

_{7}Cobb angle and spinopelvic parameters (Table 8).

### 8. The relationship between the thoracic and cervical spine parameters

_{7}slope and TK in the lumbar (

*r*=0.2,

*p*=0.01) and cervical (

*r*=0.2,

*p*=0.03) groups. The TK correlated significantly with the C

_{1}C

_{2}Cobb angle in the cervical group (

*r*=0.2,

*p*=0.01) and with the C

_{2}C

_{7}Harrison angle in the post-surgical subjects (Tables 4, 5, 7). As with the spinopelvic parameters, there was no correlation between the thoracic and cervical spine parameters in the asymptomatic group (Table 6). Regardless of the subgroups, C

_{7}slope was the only cervical parameter that was associated with TK in all the study subjects (Table 8).

### 9. The relationship between the occipital and cervical spine parameters

_{C}C

_{2}Cobb angle and C

_{1}C

_{2}Cobb angle (

*r*=0.2,

*p*=0.01) and between the O

_{C}C

_{2}Cobb angle and C

_{7}slope (

*r*=0.283,

*p*=0.006) in the asymptomatic subjects (Table 6). The lumbar and cervical groups did not show any significant correlation between the occipital and cervical parameters (Tables 4, 7). Regardless of the subgroups, both studied occipital parameters correlated with the C

_{1}C

_{2}Cobb angle (O

_{C}C

_{2}Cobb angle:

*r*=0.173,

*p*=0.000 and O

_{C}C

_{7}Cobb angle:

*r*=0.1,

*p*=0.02) (Table 8).

### 10. Multiple regression analysis and the linear regression model

_{0}C

_{7}angle (CL) as a dependent variable and regarding C

_{0}C

_{2}, TK, PI, and LL as independent variables to model the relationship between C

_{0}C

_{7}angle and potential factors by fitting a linear equation to the data. The equation for predicting the alignment of CL was as follows: C

_{0}C

_{7}angle=0.15 (C

_{1}C

_{2})+0.8TK+0.03PI−0.04LL−32.

### Discussion

_{C}C

_{2}and C

_{2}C

_{7}Cobb angles as −12.7° and −15.8° for asymptomatic subjects, −10.4° and 18.9° for patients with cervicalrelated symptoms, and −11.9° and −21.2° for post-surgical patients, respectively. In our study, O

_{C}C

_{2}angle was −14.7° for the asymptomatic patients, −14.3° for the patients with lumbar-related symptoms, −14.4° for those with cervicalrelated symptoms, and −14.5° for post-surgical patients. The C

_{2}C

_{7}Cobb angle was −15.4°, −16.8°, −17.1°, and −16.34° in our four study group, respectively. These results are similar to those of Nunez-Pereira et al. [14] relatively. Also, the total amount of CL (O

_{C}C

_{7}Cobb angle) in our study was similar to that of previous studies (−29.8°±5.6°) [14,15]. A study of Guo et al. [15] showed slight differences with regard to age in the occipitocervical alignment of healthy volunteers. In our study, age correlation was observed only with C

_{2}C

_{7}Cobb angle and C

_{2}C

_{7}Harrison angle for patients with cervical-related symptoms. The age-related structural changes in the spine justify this difference.

_{1}C

_{2}Cobb angle correlated with the three spinopelvic parameters (LL:

*r*=0.2,

*p*=0.002; PI:

*r*=−0.2,

*p*=0.02; PT:

*r*=−0.2,

*p*=0.02), and the C

_{2}C

_{7}Cobb angle correlated with PT (

*r*=0.2,

*p*=0.02) in cervical symptomatic patients. These results are consistent with those of Nunez-Pereira et al. [14] and Lee et al. [16]. Shao et al. [17] performed measurements in asymptomatic healthy volunteers and found that CL correlated with LL (

*r*=0.1, p<0.01) and O

_{C}C

_{2}Cobb angle correlated with SS (

*r*=−0.1, p<0.05). In our study, regardless of the patients’ symptoms (n=420), C

_{1}C

_{2}Cobb angle correlated with LL (

*r*=0.1,

*p*=0.01) and C

_{2}C

_{7}Harrison angle correlated with PI (

*r*=0.1,

*p*=0.04) and PT (

*r*=0.12,

*p*=0.003). It seems that pain promotes compensatory flexion to increase spinal canal volume that leads to segmental alignment changes, and this can be a factor in the change of the correlation between spinal parameters in patients with cervical pathologies compared to the asymptomatic individual.

_{0}C

_{7}Cobb angle) and spinopelvic parameters in asymptomatic, cervical symptomatic, and lumbar symptomatic patients. However, regardless of the patients’ symptoms (n=420), there was a significant relationship between C

_{0}C

_{7}angle and PI and LL. This will clarify the key role of sample numbers in evaluating the correlation between the parameters.

_{7}slope as a predictor of the overall sagittal balance of the spine. They believe that if C

_{7}slope is altered on cervical radiographs, a full-length sagittal radiograph should be taken to rule out the overall sagittal imbalance. However, we found a negative correlation between C

_{7}slope and C

_{7}SVA, and, in contrast to Nunez-Pereira et al. [14], this correlation was not statistically significant. Thus, we believe that further studies with higher sample sizes are needed to examine the role of C

_{7}slope in the overall sagittal balance of the spine.

_{7}SVA represents the global spinal sagittal alignment; thus, it should have a specific impact on CL to maintain sagittal balance, independent of other parameters. Subjects who had a positive SVA displayed an increase in CL, regardless of whether their SVA was within the normal range of values. This is a compensatory mechanism to maintain a horizontal gaze in response to changes in sagittal global alignment [11]. Interestingly, C

_{7}SVA was the only parameter in our study that showed a significant correlation with the C

_{2}C

_{7}Cobb angle in the four groups (

*r*=−0.6 in asymptomatic; −0.8 in lumbar; −0.8 in cervical; and −0.6 in post-surgical subjects). However, there was no correlation between C

_{7}SVA and total CL (O

_{C}C

_{7}Cobb angle). Matsubayashi et al. [18] found a similar significant correlation (

*r*=0.5) in normal adults. They divided the C

_{2}C

_{7}angle into the C2–C4 (middle cervical) and C5–C7 (lower cervical) angles and found that C

_{7}SVA correlated with the C5–C7 angle but not with the C2–C4 angle.

_{0}C

_{1}and C

_{1}C

_{2}) whereas the lower segment (C

_{2}C

_{7}) is associated with lateral bending [19,20]. Therefore, the difference in correlation between these two cervical subsegments and the spinopelvic parameters is not surprising. According to our study results, it seems that spinopelvic parameters (such as, PI, PT, and LL) show greater correlation with the upper cervical segment (C

_{1}C

_{2}Cobb angle) and that the total CL and the sub-axial parameters (C3–C7) are less affected.

### Conclusions

_{7}SVA and C

_{2}C

_{7}Cobb angle. Overall, the results of this study could help to better understand the cervical sagittal alignment and serve as preliminary data for planning surgical reconstruction procedures.