Abstract 
Background: The study of the angles between the vertebrae and the curvatures of the spine plays an important role in the pathogenesis of spinal disorders. The nature of the cervical region makes it susceptible to various cervical disorders, many of which can be caused by imbalanced alignment. 
Methods: In the present study, patients with chronic neck pain were compared with the normal population for cervical indexes. 
Results: One hundred subjects were selected, including 57 males (57%) and 43 females (43%). Neck tilting was significantly lower in the case group than control (41.5 vs. 45.8) (p=0.01). The mean of C0-C2 angle did not differ between groups (p=0.503), however, a significant increase was found for C2-C7 and C0-C7 angles (p=0.012) and (p=0.05), respectively. Further analysis revealed that cranial offset (21.9 vs. 8.6) and cranial tilting (21.3 vs. 10.1) significantly increased in patients with chronic neck pain (p<0.001) and (p=0.004), respectively. Also, cervical Sagittal Vertical Axis (SVA) has shown a significant increase in patients than control (24.8 vs. 9.7) (p<0.001). 
Conclusion: The data have indicated that cervical indexes. Thus, spine surgeons should obtain standing cervical radiographs and evaluate the relationship between T1 slope, Spino Cranial Angle (SCA), and cSVA in all cases affected by cervical pathogenesis, even without obvious deformity. 
Keywords: Humans, Lordosis, Male, Neck pain 

Introduction 
The study of the angles between the vertebrae and the curvatures of the spine plays an essential role in the pathogenesis of spinal disorders. Cervical region pains significantly affect people’s quality of life, and trauma alone is responsible for 85% of cervical injuries (1). The most reported statistics are chronic pains that worsen over time and occur without a specific etiology (1,2). Cervical pains are related to various anthropometric, postural, muscular, and movement variables and indices. On the other hand, unlike the thoracic and lumbar regions, cervical injury is associated with extensive pathogenesis and causes more disabilities, especially in the lower limbs (3,4). Most of the studies conducted in improving this category of patients are more focused on risk factors such as age, underlying disorders, race, and even the type of occupation of individuals (5,6).
The nature of the cervical region makes it susceptible to various cervical disorders, many of which can be caused by imbalanced alignment. Chronic pressure, stress, injuries, and degenerative diseases may also be involved in developing neck pain (7,8). 
Injury to this area can damage the bones, ligaments, or even the arteries that carry blood to the brain. Several cervical spine parameters, including C7 slope, T1 slope (T1S), C2C7 offset, C2C7 lordosis, Spino Cranial Angle (SCA), the cervical Sagittal Vertical Axis (cSVA), Thoracic Inlet Angle (TIA), and Neck Tilt (NT) have been proposed to assess sagittal balance in asymptomatic, scoliosis, and elderly subjects (9).
Cervical spine deformity develops consequently abnormal head posture compared to the chest and shoulders, accompanied by breathing and swallowing difficulty (10). Congenital, trauma, inflammatory, and iatrogenic are some of the causes of cervical spine deformity (11). 10-20˚ was declared as normal cervical lordosis (11). There is a need to understand how cervical spine sagittal deformity relates to cervical symptoms and health-related quality of life. Among the essential topics, the cervical sagittal parameters are widely used in evaluating cervical spine disorders and surgery. In this regard, the present survey investigates the changes in cervical indexes on cervical pain development. 

Material and Methods 
Study population 
In the present case-control study, patients with neck pain for at least six months were compared with the normal population. Subjects without neck pain were considered for control, although after demonstrating normal cervical lordosis, they were included as the control group.  
Inclusion criteria for selection were lack of trauma history and no history of specific diseases associated with neck musculoskeletal disorders. Patients who were candidates for surgery and congenital disorders in the cervical spine were excluded. The current study is based on the ethical committee of Medical Sciences (IR.AJUMS.HGOLESTAN.REC.1399.093).

Angle measurement 
Cervical spine radiographs (vertically, horizontally, and laterally) were taken from all the patients standing and in a neutral head position in the Frankfurt horizontal plane. Since the Frankfurt plane extends from the upper limit of the external ear hole to the lower limit and the lower border of the orbit, it is the best line for placing the skull in a natural state. In this regard, it is considered for the present study. To improve the diagnostic accuracy, all the graphs were evaluated by an experienced radiologist. Cervical lordosis was divided into two parts, the upper cervical lordosis, including the C0-C2 angle, and the lower cervical lordosis, consisting of the C2-C7 angle.

Cobb measurement 
Cobb angle is the most widely used measurement for quantifying spine curvature. The measurement method includes choosing the most crooked bead in the upper part of the beads and the most crooked in the lower part and then drawing two tangent lines on these two beads by the user. The characteristic angle of the intersection of these two lines is the Cobb angle. Parameters including T1S, C0-C2 angle, C0-C7 angle, neck tilting, C0-C2/C2-C7 ratio, C2-C7/C0-C7 ratio, C0 angle, C2-C7 angle, cranial offset, cranial tilting, cranial SVA, and TiA were measured. The measurements were done using a negatoscope and radiant software.

Statistical analysis
All the data were analyzed by SPSS software (IBM SPSS, Version 22). Quantitative data were analyzed using descriptive tests and presented as Mean±SD. The mean of parametric data between the two groups was analyzed using an independent sample t-test. A p-value < 0.05 was considered statistically significant.

Results 
One hundred subjects were selected, including 57 males (57%) and 43 females (43%) (Table 1). 

Table 1. The demographic information of the participants

Neck tilting was significantly lower in the case group than control (41.5 vs. 45.8) (p=0.01). The mean of C0-C2 angle did not differ between groups (p=0.503); however, a significant increase was found for C2-C7 and C0-C7 angles (p-value =0.012) and (p-value = 0.05), respectively (Table 2). In contrast, the C0 angle has not differed between the two groups; hence, significant differences were not found between groups for C0-C2/C2-C7 ratio and C2-C7/C0-C7 ratio (p-value >0.05) (Table 2). 

Table 2. Comparing two groups for the cervical parameters

Thoracic inlet angle (TiA), Sagittal Vertical Axis (SVA).

Further analysis indicated that cranial offset (21.9 vs. 8.6) and cranial tilting (21.3 vs. 10.1) significantly increased in patients with chronic neck pain (p-value <0.001) and (p-value = 0.004), respectively (Table 2). Also, cervical SVA has shown a significant increase in patients than control (24.8 vs. 9.7) (p-value <0.001) (Table 2).  
Regardless of the groups, all the parameters were compared between the two genders. The results did not show any significant differences (p-value>0.05) (Table 3). 

Table 3. The differences between the two genders for cervical parameters

Thoracic inlet angle (TiA), Sagittal Vertical Axis (SVA).

Discussion 
Knowing the exact number of spinal curvatures can effectively prevent, diagnose, and treat spinal abnormalities (12). There is no standard method for assessing cervical sagittal alignment (13). Previous studies have reported normal ranges or abnormal values of parameters such as T1 slope, cSVA, and SCA to measure cervical sagittal alignment parameters (14,15).
In the present survey, the mean of cervical parameters was compared between the normal population and patients with chronic neck pain. Our results have indicated a significant difference between the two groups for T1 slope, neck tilting, and C0-C7 angle. In the same investigation, a T1 slope less than 40 degrees is optimal for favorable sagittal balance (16). 
Considerable literature has demonstrated that factors such as age, BMI, and gender directly influence cervical sagittal; also, it was shown that T1 slope and cSVA in males with aging increase (17). It contrasts with our findings; our data do not differ significantly between the sexes for cervical parameters. It should be noted that the T1 slope is one of the essential parameters of sagittal spine balance. However, due to the overlying anatomic structures, the end plane of T1 is difficult to visualize on radiographs. Recently, researchers have shown that upper and lower C7 slopes are highly correlated with the T1 slope and can be used as a surrogate for T1 slope estimation when the T1 endplate is poorly visualized (18).
Additionally, the C2 slope can be represented by T1s minus cervical lordosis and show the same changes with each other (19).
Further analysis revealed that with increasing T1 slope, the C2-C7 angle rises, too. Along with our data, the SVA C2-7 decreases with the T1 slope increase (20). Also, the T1 slope directly influences the C2-C7 angle (21), in accordance with our data that the C2-C7 angle significantly differs between normal population and asymptomatic patients. In this line, the higher T1 slope and cSVA can be considered for predicting kyphosis following laminoplasty (22). No association was found between C0-C2 angle and neck pain development, where it demonstrated that kyphosis improved with C0-C2 compensation (23,24).  
Thoracic inlet alignment significantly influenced the cervical tilting (25), which is in agree with our findings. Our data have demonstrated that cranial offset considerably is higher in the case group. Knott et al’s results agreed that T1 slopes more than 30 degrees are accompanied by thoracic deformity (26). 
Initial observations suggested that age affects cervical sagittal balance. With aging, the motion ranges are reduced in the cervical spine. However, this variation does not follow a regular pattern since it increases in some ages and decreases in others (27). With aging, the T1S of the first dorsal vertebra increases, and C2-C7 lordosis is followed by C0-C7 increase (28). Age results in destructive degeneration affecting the joint’s alignment. These alterations cause tolerance reduction against the additional extensor forces (29). 

Limitations 
The absence of parts of the skull bone, such as nasion and opisthion, as well as the upper end plate of the T1 vertebra or the sternum in some simple radiographs, limits the detailed examination of the indices. In this regard, it is suggested to evaluate these areas with higher accuracy in the imaging field in future studies.

Conclusion 
Based on the findings of the present survey, it is believed that spine surgeons should obtain standing cervical radiographs and evaluate the relationship between T1 slope, SCA, and cSVA in all cases affected by cervical pathogenesis, even without obvious deformity. Future studies should investigate the clinical correlates of cervical spine disorder and T1 slope, SCA, and cSVA to confirm the influence of these parameters on clinical outcomes.

Consent for publication
Informed consent was obtained from all individual participants included in this study.

Ethical approval
The current study is based on the ethical committee of Ahvaz Jundishapur University of Medical Sciences (IR.AJUMS.HGOLESTAN.REC.1399.093). 

Acknowledgement
We thank the patient for his consent to publish the case report. The authors would like to thank the colleagues at Golestan Hospital, Ahvaz Faculty of Medical Sciences, for their guidance and encouragement.

Conflict of Interest
No potential conflict of interest relevant to this article was reported.