CORRELATION BETWEEN CERVICAL SAGITTAL ALIGNMENT AND FUNCTIONAL CAPACITY IN CERVICAL

Objective: To correlate the radiographic parameters of sagittal cervical alignment with quality of life and functional capacity in patients with cervical spondylosis under conservative treatment. Methods: This is an observational and prospective study in patients with cervical spondylosis under conservative treatment and without indication for surgery. The 52 patients included were divided into three groups: axial pain, radiculopathy, and cervical myelopathy. The radiographic parameters considered were cervical lordosis (CL), cervical sagittal vertical axis (CSVA), T1 slope (TS) and the discrepancy between TS and CL (TS-CL). Quality of life and functional capacity were evaluated by the Neck Disability Index (NDI) questionnaire. Pain was assessed by the Visual Analogue Scale (VAS). The correlation between the radiographic parameters and the clinical scores was evaluated by the Pearson correlations coefficient. Results: There was no difference in cervical radiographic parameters between the three groups. In the total of the sample, the mean value of the CSVA was 17.8o (±8.3o), CL, 22.4° (± 8.8°); TS, 29.3° (±6.6°), and TS-CL, 7.0° (±7.4°). Significant inverse correlation (r= -0.3, p=0.039) was observed between NDI and CL, but there was no significant correlation between CL and VAS. CSVA (p=0.541), TS (p=0.287) and TS-CL (p=0.287) had no significantly correlated with NDI or VAS. Conclusion: Considering patients with cervical spondylosis not candidates for surgery, the only sagittal parameter that correlated with functional capacity was LC. In these patients, the correlation between cervical alignment and quality of life needs to be better characterized.


INTRODUCTION
The cervical region is the spinal segment with the most mobility, in addition to being responsible for support of the weight of the head, and is susceptible to a series of pathologies associated with significant compromise to quality of life and functional disability. 1,20][11] It has also been shown that in addition to the analysis of overall sagittal alignment, i.e., of the sagittal vertical axis, the pelvis plays a fundamental role in spine alignment, functioning as a tool to compensate for the loss of overall sagittal alignment and also correlating with quality of life indicators. 8,12,135][16][17] Standing out among the radiographic parameters most used to evaluate cervical alignment are cervical lordosis (CL) as defined by the Cobb method, based on lines parallel to the lower terminal plates of C2 and C7; 18 the cervical sagittal vertical axis (cSVA), measured by the perpendicular distance between a plumb line drawn from C2 and the posterior-superior aspect of the vertebral body of C7 2 ; and the discrepancy between the T1 slope (TS) and cervical lordosis (CL), calculated by the arithmetic expression TS-CL, which, according to some authors, acts as the cervical equivalent to the discrepancy between pelvic incidence and lumbar lordosis for the lumbar spine. 19ven though the correlation between such radiographic parameters of cervical sagittal alignment with quality of life and postoperative outcomes in patients submitted to surgical treatment is well-established, 15,20,21 there is a scarcity of evidence in the literature of any correlation between cervical sagittal parameters and loss of quality of life or functional disability in patients in conservative treatment.Thus, the objective of this study is to evaluate and correlate radiographic parameters of cervical sagittal alignment with quality of life and functional disability indicators in patients with cervical spondylosis in a conservative outpatient treatment regimen who are not candidates for surgical treatment.

METHODS
This is an observational, prospective study, approved by the Institutional Review Board (IRB) of the responsible service (opinion no.1.445.245).Participating in the study were patients attended at the outpatient spine pathology clinic of the same service, all having filled out the Informed Consent Form approved by the IRB.Individuals over 18 years of age with a diagnosis of cervical spondylosis undergoing a conservative treatment regime and who were not candidates for surgery were included.Individuals with spinal pathologies other than spondylosis (such as neoplasias, trauma, and congenital deformities), prior spine surgeries, patients with neurological disease, psychiatric conditions that compromise their understanding of the study, and patients who were indicated or opted for surgical treatment of their cervical spine condition were excluded.The patients were divided into three groups by clinical profile: Axial pain, Radiculopathy and Cervical myelopathy.
Lateral total spine radiographs of the patients were taken in a standing position with their eyes fixed on the horizon.Only exams that permitted adequate visualization from the base of the skull to the first thoracic vertebra (T1) were considered.The digitalized images obtained were analyzed using Surgimap Spine software (Nemaris Inc., New York, USA) to measure the following radiographic parameters of cervical sagittal alignment: cervical lordosis (CL), cervical sagittal vertical alignment (cSVA), the angle of inclination of T1 (TS), and the difference between the T1 inclination and the cervical lordosis (TS-CL), as illustrated in Figure 1.Quality of life and desability were evaluated using the Neck disability index (NDI) questionnaire translated and validated for the Portuguese language. 22For the evaluation of the intensity of cervical axial pain, the Visual analog scale (VAS) was used, graded from 0 to 10, where 0 equals the absence of pain and 10 the strongest pain the patient has ever felt. 23tatistical analysis was performed using STATA 11 SE software.The normality of the variables was tested by the Shapiro-Wilk test and the correlation analysis was tested by calculating the Pearson correlation coefficient.The comparison of the radiographic parameters between the patients with axial pain, radiculopathy, or myelopathy was conducted by means of the ANOVA test.A significance level of 5% was considered, therefore the results with a value of p lower than 0.05 were considered to be statistically significant.

RESULTS
The study included 52 patients with an average age of 60 years, ranging from 24 to 84 years of age with a standard deviation of 12 years.The sample was made up of 38 female patients (73%) and 14 male patients (27%).Of the total number of patients analyzed, 43 (82.7%) were classified as Axial Pain, 3 (5.8%)as Myelopathy, and 6 (11.6%) as Radiculopathy.Taking the total sample into account, the average cSVA was 17.8° (±8.3°), the average CL, 22.4° (±8.8°); the average TS, 29.3° (±6.6°), and the average TS-CL difference, 7.0° (±7.4°).Comparing the cervical sagittal alignment parameters in terms of classification by diagnosis, no significant difference was found for any of the parameters studied.(Table 1) Table 2 shows the study of correlation between the radiographic parameters and the age of the patients of the study.There was a correlation with the cSVA (r = 0.3) and the TS (r = 0.3), both of them weak, but statistically significant (p = 0.04 and p = 0.03, respectively) and a moderate statistically significant correlation (r = 0.04, p < 0.001) with the CL.There was no statistically significant correlation between age and TS-CL.Considering the radiographic cervical sagittal alignment parameters among themselves, there was a moderate correlation (r = 0.4, p = 0.004) between the cSVA and the TS and between the CL and the TS (r = 0.6, p < 0.001).(Table 3)

DISCUSSION
5][26] More recently, there has been an increase in the number of studies demonstrating that there is also an important correlation between the postoperative outcomes of spine interventions and sagittal parameters. 15,20,27However, studies that correlate cervical sagittal parameters with quality of life indicators in patients who were not submitted to surgical treatment are extremely rare.This study analyzed the correlation of these radiographic parameters with indicators of quality of life and functional ability in a sample of patients with cervical spondylosis without an indication for surgical treatment or who opted not to undergo surgical treatment.
Tang et al. 15 demonstrated the cSVA as an independent predictor of functional outcomes in patients submitted to posterior spinal arthrodesis.Thereafter, the cSVA was associated with worse severity of cervical myelopathy. 16In this study, there was no evidence of a correlation between the cSVA and quality of life, although the sample was made up of patients with no indication of surgical treatment or who had opted out of surgery.In addition, only 5.8% of the patients included had a diagnosis of myelopathy.
Our study results showed a significant inverse correlation between the CL and the NDI: the higher the value of the CL, the lower the value obtained from the NDI, i.e., the better the functional ability of the patient.In a recent study, Iyer et al. 28 analyzed the correlation between radiographic sagittal alignment parameters and quality of life in the preoperative period in patients awaiting surgical procedure.An inverse correlation was observed between the CL and the NDI, in that an increase in the CL was also associated with lower NDI values, similar to what was observed in our study.However, in their study, Iyer et al. 28 divided the patients into two groups -myelopathy and radiculopathy -and there was a significant correlation between the radiographic parameters and the NDI in the patients with myelopathy, but not in the patients with radiculopathy.Again, the vast majority of the patients in our study were classified as suffering from axial pain and radiculopathy (94%), and the minority with myelopathy.
The correlation between the cervical sagittal alignment parameters themselves has been demonstrated in recent studies, 1,21,29 as well as the role of the cervical-thoracic junction in cervical sagittal alignment, similar to what occurs in alignment of the thoracolumbar spine in correlation to the pelvis. 2,13The correlation between the TS and the CL, showing that the amount of CL is influenced by the inclination of the upper plateau of T1 (TS), has been published in the literature 21,29,30 and was also evident in our study.A significant correlation between the TS and the cSVA was also confirmed, which indicates the important role of the inclination of T1 for all cervical sagittal alignment, as previously demonstrated in the literature. 2,29,30his study also showed the effect of aging on cervical sagittal alignment.As seen in the results obtained, the TS, the CL, and the cSVA tend to increase with age.Yukawa et al. 30 published similar results and argued that with age the spine tends to assume positive sagittal alignment, increasing the TS.In order to maintain the ability to look forward, the cervical spine has an increase in the value of cervical lordosis.
The main limitation of this study was the small case series and also the fact that few cases were included (15.3%) that could be classified as patients with "cervical spine deformity", according to the criteria of the recently published classification system for cervical deformity. 31The fact that very few of the patients in the sample did not have indicators for a diagnosis of deformity and that the study only included patients who were not candidates for surgical treatment or who opted for non-surgical treated may suggest that the patients without criteria for deformity are more favorable to non-surgical treatment than patients with cervical spine deformity.
It seems incontestable that cervical alignment is a direct indicator of functional outcomes and of the quality of life following cervical spine arthrodesis and that the existence of a well-established correlation   The analysis of the intensity of cervical axial pain in the patients, through the VAS, showed an average of 6.8 (±2.5), considering the total sample.The study of the correlation of the VAS with the cervical sagittal alignment parameters, illustrated in Table 3, did not show any significant correlation of cervical pain with any radiographic parameter (p > 0.05).The average score obtained for the NDI questionnaire, considering the total sample, was 39.1 (±16.5),ranging from 8 to 84.Table 4 shows the correlation of the NDI score with the radiographic cervical sagittal alignment parameters.There was an inverse correlation of weak intensity (r = -0.3),though statistically significant (p = 0.039), between the CL and the NDI.(Figure 2) There was no significant correlation between the NDI and any of the other radiographic parameters considered.between radiographic cervical alignment parameters and quality of life has been demonstrated in patients with myelopathy and cervical spine deformity.However, in patients with cervical spondylosis presenting axial pain and radiculopathy, without myelopathy and without deformity, this correlation has not been well-established.

CONCLUSIONS
Considering a sample of patients with cervical spondylosis without indications for surgical treatment or who opted for non-surgical treatment, the only radiographic cervical spine alignment parameter that was correlated with quality of life was cervical lordosis.In these patients, presenting axial pain and radiculopathy, without myelopathy and without deformity, the correlation between cervical alignment and quality of life need to be better characterized.

Figure 1 .
Figure 1.Example of a digitalized image with measurements of the radiographic parameters of interest (cSVA, TS, and CL) using Surgimap Spine software (Nemaris Inc., New York, USA).

Figure 2 .
Figure 2. Correlation between the NDI and cervical lordosis.

Table 1 .
Values of the cervical sagittal parameters according to each diagnosis.

Table 2 .
Correlation of the cervical sagittal parameters with age.

Table 3 .
Values of the correlations (r) between the variables studied.

Table 4 .
Correlation of the NDI with cervical sagittal parameters.