Correlation between cervical lordosis and cervical disc herniation in young patients with neck pain

Abstract

Abnormal cervical curvature and cervical disc herniation are closely related to neck pain and should be taken into account before any treatment. However, studies have rarely reported on the correlation between cervical lordosis and cervical disc herniation in patients with neck pain. Therefore, in this study, we collect young neck pain patients with abnormal cervical curvature to evaluate the relationship between cervical lordosis and cervical disc herniation.

Three hundred patients below 40 years old with neck pain were enrolled. Patient sex, age, apical vertebra, segment of intervertebral disc protrusionl, sagittal diameter of spinal duramater, saggital diameter of spinal canal, height of disc space were recorded, and the cervical curvature, and degree of cervical spinal cord compression (G/F ratio) were calculated. The change of degree of disc herniation and degree of cervical spinal cord compression were analyzed in different cervical curvature groups. Further more, collected these patients who had improved cervical curvature over a period of time, to compare the changes of degree of disc herniation, G/F ratio, and height of disc space.

The median age of patients with kyphosis was lower than those with lordosis and straight cervical spine. The degree of disc herniation was higher in the straight and kyphosis groups compared to the lordosis group. Cervical lordosis was inversely correlated with the degree of disc herniation and positively with G/F ratio. Cervical curvature was significantly affected by sex, age, and the degree of disc herniation. With the improvement of cervical lordotic curvature, the degree of disc herniation decreased and height of disc space increased.

The degree of disc herniation and cervical spinal cord compression are inversely correlated to cervical lordosis in young neck pain patients, and the degree of disc herniation and height of disc space can recover with the recovery of cervical lordotic curvature. These findings may indicating a link between cervical curvature and degenerative changes which have important clinical implications.

1. Introduction

Chronic neck pain is a common affliction in middle-aged and elderly patients with 30% to 50% prevalence, and seriously affects their quality of life. The etiology of neck pain is complex and possibly related to disc herniation, facet joints, muscles, and ligaments.^[1–2] Due to excessive movement of the cervical spine, long-term bad posture and lifestyle choices, and soft tissue damage in the neck, cervical stability gradually decreases and can lead to the loss of cervical lordosis.^[3]

Abnormal cervical curvature, including excessive or meagre cervical lordosis, loss of cervical curvature, kyphosis, and complex cervical curvature, is an early manifestation of degenerative changes in the spine.^[4] The normal cervical curvature is essential for maintaining balance and motor function, and any of the aforementioned abnormalities can destroy cervical spine structure, leading to biomechanical dysfunction, bone hyperplasia, cervical muscle injury, and ultimately cervical spondylosis.^[5–7] Therefore, it is very important to restore the normal cervical curvature while treating cervical spondylosis.

Cervical disc herniation should also be taken into account before any treatment since many patients with abnormal cervical curvature have accompanying disc herniation. In addition, the prevalence of disc herniation is reportedly 2% to 23% (median 11%) among asymptomatic volunteers.^[8] However, little is known regarding a potential relationship between cervical curvature abnormalities and disc herniation, or whether they affect each other. Therefore, the aim of this study was to evaluate the correlation between cervical lordosis and cervical disc herniation in patients with neck pain. Early observation of the severity of disc herniation can better guide clinical diagnosis and treatment, and prevent the aggravation of neck pain.

2. Patients and methods

2.1. Patient characteristics

Three hundred patients (139 males and 161 females, mean age 31.44 ± 5.02 years, age range 16–40 years) with neck pain who were treated at the Department of Orthopedics, Shenzhen Hospital of Traditional Chinese Medicine between January 1, 2014 and August 31, 2018 were included in this cross-sectional study. Patients with congenital dysplasia, trauma, pathology, tumor, severe osteoporosis, and cervical spine surgery were excluded. In this study, written or verbal consent was obtained from all the patients. The study was approved by the ethics committee (EC) office of Guangzhou University of Chinese Medicine, and the rights of the subjects were protected.

2.2. Imaging and clinical assessment

All patients underwent cervical X-ray and magnetic resonance imaging (MRI) detection at the Medical Imaging Center, Shenzhen Hospital of Traditional Chinese Medicine. The X-rays were taken with the patients in a standing but comfortably neutral resting position. The following lines were drawn on the lateral radiographs of cervical vertebras according to Borden's method^[4]:A—between posterior superior marginal of C2 odontoid process and posterior inferior edge of C7 vertebra, B—along the trailing edge of the cervical vertebrae, C—the longest distance between line A and B as the cervical curvature value, and D—apical vertebra (Fig. 1A). To determine the disc space heights in MRI, the following lines were drawn: E—between the inferior and superior end plate, F—the sagittal diameter of spinal canal, and G—the sagittal diameter of spinal dura mater (Fig. 1B). The degree of cervical spinal cord compression was calculated in terms of the G/F ratio. Finally, the line H was drawn on the transverse MRI section to determine the degree of disc herniation (Fig. 1C).

Figure 1.

The lines drawn on each cervical spine radiograph. (A) lateral radiograph. (B) MRI at the sagittal position. (C) MRI of transverse section. MRI = magnetic resonance imaging.

Based on the assessment of X-rays and MRIs, the apical vertebra, segment of intervertebral disc protrusion, the sagittal diameter of spinal dura mater, the sagittal diameter of spinal canal, height of disc space, cervical curvature, and G/F ratio were calculated. Patients were then divided into 3 groups on the basis of cervical curvature: kyphotic: C ≤0 mm, straight: 0 mm <C ≤7 mm, and lordotic: C >7 mm.

2.3. Statistical analysis

SPSS 19.0 software (SPSS Inc., Chicago, IL) was used for statistical analysis. Continuous data were expressed as the mean±standard deviation. Data with non-normal distribution were converted to the logarithmic form and compared by Mann–Whitney U tests. Normally distributed data were compared by independent Student t test. Categorical data were expressed in percentages and compared by chi-square test. Correlation between variables was determined by Pearson correlation and multivariate linear regression analysis. P values <.05 were considered statistically significant.

3. Results

3.1. Basic characteristics of all patients

The clinical characteristics of the patients are summarized in Table 1. Based on the cervical curvature, the patients were classified into the lordosis (n = 96), straight (n = 99) and kyphosis (n = 105) groups (Fig. 2). There were 201 segments of intervertebral disc herniation, including C3/4 (13), C4/5 (53), C5/6 (121), and C6/7 (14), and the apical vertebra were C4 (72), C5 (210), and C6 (18).

Table 1.

Basic clinical characteristics of all patients.

Figure 2.

The type of cervical curvature according to the lateral cervical spine radiograph: (A) lordosis, (B) straight, (C) kyphosis, and (D) sigmoid.

3.2. The degree of disc herniation was higher in loss lordosis patients

The median age of the kyphosis patients was lower compared to the lordosis and straight spine groups (30.38, 31.30, and 32.69 respectively). In addition, a higher number of female patients were seen in the straight (61.6%) and kyphosis groups (61.9%) compared to the lordosis group (36.5%). The degree of disc herniation in the straight (1.58 ± 1.49) and kyphosis (3.31 ± 1.50) groups were higher than that in the lordosis group (0.88 ± 1.31). The G/F ratio, which reflects the degree of cervical spine compression, showed a tendency to decrease with decreased cervical lordosis (median, 0.72 vs 0.66 vs 0.64, P <.001) (Table 2).

Table 2.

Demographic findings of patients with lordosis, straight cervical spine and kyphosis.

3.3. Correlation of cervical curvature with clinical variables

The correlation between the cervical curvature and clinical variables is summarized in Table 3, and shows an inverse correlation with the degree of disc herniation, and positive with G/F ratio (r = −0.583 and 0.315, P <.001 and <.001 respectively). Multivariate linear regression analysis showed that cervical curvature was affected by sex, age, and the degree of disc herniation. The regression equation was Y = 2.033 − 1.790X1 + 0.194X2 − 1.913X3 (R = −0.613, F = 29.333, P <.001).

Table 3.

The correlation of cervical curvature with age, sex, degree of disc herniation, G/F ratio, and disc space heights.

3.4. The degree of disc herniation and height of disc space recovered with the recovery of cervical curvature

We followed up the patients who showed improved cervical lordosis over a period of time and compared the different clinical variables between the first and last visits. It showed that a decreased degree of disc herniation was observed along with increased cervical lordosis (median, 2.58 vs 1.51, P = .003). Height of disc space in last visit (8.71 ± 9.59) were increased compared to that at the first visit (6.79 ± 1.06) (P = .013, Table 4). There was no significant change in the G/F ratio.

Table 4.

Multivariate linear regression analysis of factors influencing cervical curvature.

4. Discussion

Cervical lordosis is the first physiological curvature of the human spine, and due to its load-bearing function, a predominant site of disc herniation. It maintains the stability of the spine and is an important part of normal spinal biomechanics,^[8,9–10] in addition to cushioning the vibrations.^[11] In recent years, the lifestyle of the younger demography has become increasingly sedentary, with students and office workers spending long hours sitting in front of their computers, resulting in higher incidence of cervical curvature abnormalities. Zhou studied 2106 Chinese teenagers with neck pain and reported 37 (61.67%), 430 (71.67%) and 1105 (76.42%) cases of abnormal cervical curvature in the 6 to 15 years, 16 to 25 years, and 26 to 35 years age groups respectively.^[12] Cui et al randomly selected 4681 students for cervical spine examination,^[13] and noted 1362 cases (29.1%) with abnormal curvature. Kang et al imaged 3261 patients with cervical spondylosis and found 1886 (57.81%) with abnormal cervical curvature.^[14] The latter can be measured by various means, such as Borden measurement, cervical curvature index (CCI), Cobb angle measurement, and tangent angle measurement of posterior edge of vertebral body.^[4] Since Borden measurement is the most widely used method at present and has the advantage of reproducibility in multiple operations,^[15] we used this method in our study as well. Although several studies have reported a relationship between sagittal alignment and intervertebral discs during cervical spine surgery, little is known regarding the degenerative changes of the cervical spine.^[16–19] In patients with high cervical lordosis, anterior cervical discectomy without fusion affects the sagittal alignment of the entire spine. Normalizing the angle of cervical lordosis can lead to reciprocal changes in pelvic tilt and sacral slope.^[16]

The main finding of this study was the inverse correlation between the degree of disc herniation and extent of cervical lordosis in neck pain patients, with smaller herniation accompanying increased lordosis. In addition, the degree of cervical spinal cord compression also increased with the decrease in cervical lordosis. This is the first report on such a correlation between cervical curvature and disc herniation in young patients. No study so far has been able to demonstrate whether the degenerative changes in the spine are the cause or effect of kyphosis. Han Jo Kim study found no correlation between cervical lordosis and cervical degeneration.^[18] During a 10-year follow-up study by Okada et al, posterior disk protrusion and decrease in the signal intensity of spinal discs were observed.^[20] In addition, subjects older than 40 years with non-lordosis type of sagittal alignment showed more frequent posterior disk protrusion. However, no significant correlation was detected between the sagittal alignment of the cervical spine and clinical symptoms.^[21–22] In contrast, we confirmed a strong correlation between cervical lordosis and disc herniation, which can greatly improve the diagnosis of cervical spondylosis (Table 3).

Interestingly, females tended to have less cervical lordosis compared males, although without any statistical significance, as reported by Ella Been et al^[23] Gender differences in the cervical lordosis are already apparent in children. Yukawa et al^[24] and Been et al^[25] found greater lower cervical lordosis (C2–C7) in males compared with females. Differences in the cervical lordosis angles might be related to gender differences in skull morphology, larynx, or thorax shape and size. In addition, the median age of the kyphosis patients was lower than the other groups, indicating that younger people are more likely to have severe loss of cervical lordosis. This contradicts studies reporting lack of any significant association between age and cervical lordotic curvature.^[19] The reason for this discrepancy could be the overall younger age of our cohort. Iorio et al reported a significant age-related increase in C2–C7 lordosis, C0–C7 lordosis and T1 slope, especially in subjects older than 55 years.^[26] Previous research found that the cervical lordosis is related to age. As reported that cervical lordosis becomes most pronounced with the development of the sitting position at age 9 months,^[27,28] and that the C3–C7 lordosis angle reach adult like angles at age 14 to 15.^[29] Children had more lordotic C1–C7 angle and more kyphotic FM–C1 angle. As for the correlation between the cervical lordosis and degree of disc herniation. The physiological relationship of sex, age, degree of disc herniation needs further exploration. We performed correlate analysis for age, gender, and degree of disc herniation. Single linear regression and bivariate correlation analysis all showed that degree of disc herniation was not significantly correlate with age and sex. We will discuss these aspects in the discussion of this article.

The heights of disc space in the straight cervical spine group were greater compared to the other groups, which could be due to the fact that we measured the central position of the upper and lower endplates. We also observed that some patients showed improvements in cervical kyphosis after treatment, rest or exercise, and found that the degree of disc herniation was decreased and the heights of disc space were increased after their last follow-up compared to the first visit (Table 5). These results strongly indicate that restoring the cervical curvature is vital for improving cervical disc herniation.

Table 5.

Comparison of variables between first visit and last visit.

The mechanism of the loss of cervical lordosis remains unclear, although some studies hint at the association between the neck muscles and disc compression.^[30–31,22] Alpayci et al found that the loss of cervical lordosis severely affected neck extensors more than the neck flexors in neck pain patients, although it is not possible to determine the timing of abnormal curvature and disc herniation.^[30] The degenerative cascade can cause desiccation of the intervertebral disc resulting in height loss. If the load balance and lordosis are not restored, the altered cervical curvature will eventually progress to kyphosis.^[32–33]

Our study has several limitations that should be addressed. First, we did not analyze the mechanism underlying the correlation between abnormal cervical curvature and cervical disc herniation, and second, this was a single center study on a small patient cohort. Our findings, therefore, need to be validated in multicenter studies with larger cohorts. In addition, longitudinal and molecular studies are needed to further explore the mechanism of abnormal cervical curvature and cervical disc herniation.

In conclusion, our study is the first to show that the degree of disc herniation and cervical spinal cord compression are inversely correlated to cervical lordosis in young neck pain patients, and the degree of disc herniation and height of disc space can recover with the recovery of cervical curvature. These findings provide new insights into the relationship between cervical curvature and spinal degeneration and can improve the clinical management of chronic neck pain.

Author contributions

Conceptualization: Yafei Cao.

Data curation: Kun Gao, Jiliang Zhang, Jinquan Lai, Weidong Liu, Hanqing Lyu, Yihong Wu, Zhanpeng Lin.

Formal analysis: Kun Gao, Hanqing Lyu.

Investigation: Kun Gao, Jiliang Zhang, Jinquan Lai, Weidong Liu, Yihong Wu, Zhanpeng Lin.

Methodology: Kun Gao.

Project administration: Yafei Cao.

Supervision: Yafei Cao.

Writing – original draft: Kun Gao.

Writing – review & editing: Kun Gao.

Yafei Cao orcid: 0000-0001-9193-376X.