The Correlation of Time of Cervical Flexion with Cervical Symptoms in Oce Workers: A Cohort Study

Background: An increasing number of oce workers complain of neck pain after extended smart phone use. We conducted this study to examine the correlation between the time of cervical exion (CFI) during smart phone use and cervical symptoms of oce workers in China. Methods: In this cohort study, 1791 individuals responded to an on line questionnaire. For our study, we included responses of 498 [27.8%] oce workers. Excluded from the study were 1293 [72.9%] individuals including building workers, students, non-oce workers, and those who did not complete the questionnaire. Participants completed an online questionnaire survey from May 29, 2019 to April 10, 2020. The (Neck Disability Index) NDI was used to evaluate cervical symptoms. Multivariable logistic regression, threshold saturation effect analysis, t-test, and Pearson’s chi-square tests were used to analyze the data. Results: We analyzed questionnaire results of the 498 oce workers. The t-test showed no signicant differences among the gender groups for age, working age, and NDI scores (P>0.05). Compared with other activities, smart phone use had no positive correlation with NDI scores (P>0.05), while low back pain had a strong correlation with NDI scores (P<0.05). When adjusting for age, working age, and low back pain covariates, CFI had a positive correlation with NDI scores. In addition, CFI had a curve line correlation with NDI-a monotone increasing relationship; the fold point was 6 (P<0.05). Conclusions: CFI had a positive curve line correlation with the NDI suggesting that oce workers should limit CFI to a maximum of 6 hours to decrease cervical symptoms.

China's modern era of rapid economic development, increasingly more professional o ce workers have career-related diseases such as CS.
Two region-speci c questionnaires for the cervical spine are the Neck Disability Index (NDI) and the Neck Pain and Disability Scale (NPDS) [7]. The NDI is designed to measure activity limitations due to neck pain and disability [8][9][10], whereas the NPDS measures problems with neck movements, neck pain intensity, effect of neck pain on emotion and cognition, and the level of interference during life activities [11]. NDI is easier for the lay public to understand and considered a responsive measure for neck pain and acute whiplash injury [12], we chose this scale for our analysis.
In order to improve the quality of life among o ce workers, we sought to investigate the correlation between the time of cervical exion (CFI) and the NDI among o ce workers of China, and whether the smart phone use (SPU) had a negative effect on the cervical spine. As far as we know, few scholars pay attention to the relationship between the CFI of SPU and cervical symptoms.

Data collection
We used the Questionnaire Star (https://www.wjx.cn/) to conduct a real-time online cohort survey study. The survey was conducted from May 29, 2019 to April 10, 2020. Respondents came from nationwide; the recruitment target was o ce workers. The NDI was used to assess the perceived pain and disability related to the cervical spine.

Design and setting
Cohort study.

Statistical methods
In this study, we took a purposive approach with no sample estimation. Data were analyzed using the statistical packages R (R Foundation; http://www.r-project.org; version 3.4.3) and EmpowerStats (www.empowerstats.com; X&Y Solutions Inc.). Multivariable logistic regression models, generalized estimated equation model, generalized additive models, threshold saturation effect analysis, t-test, and Pearson's chi-square tests were used to analyze the data. The mean ±standard deviation (SD) and 95% con dence interval (CI) were used to indicate the size of the value. The level of statistical signi cance was set at p<0.05.

Results
Flow chart of this study A total of 1791 individuals participated in the online questionnaire survey, with 498 (27.81%) o ce workers included, and 1293 individuals excluded. Those participants who were excluded were 563 (31.34%) individuals who did not complete the questionnaire, 218 (12.17%) students, 78 (4.36%) building workers, and 434 (24.23%) other non-o ce workers. The ow chart can be seen in Fig 1. Sociodemographic and clinical characteristics of the sample.
The baseline characteristics of all patients are shown in Table 1. The results of the t-test showed no signi cant differences among the gender groups for age, working age, and NDI scores (P>0.05), and the CFI of males was higher than that of females (P<0.05). Pearson's chi-squared test showed that differences in the number of educational degrees in the male and female groups were signi cant (P<0.05). The activities ratio of smart phone use (SPU), using computers (UC), reading books (RB), and using other electronic devices (UOED) was 63.71%/78.07%, 30.65%/18.72%, 1.61%/2.14%, and 4.03%/1.07% in the male and female groups, respectively. Pearson's chi-square tests showed differences were statistically signi cant (P<0.05). The incidence of neck pain (74.19% male, 66.31% female) and the incidence of low back pain (73.39% male, 78.07% female) were high; the difference between males and females was not signi cant (P>0.05).
Crude correlation associations of CFI, covariates, and NDI of the sample As seen in Table 2, single factor correlation analysis showed that age and working age did not have a correlation with NDI scores for participants (P>0.05). CFI had a positive correlation with NDI scores (P<0.05). Compared with other activities, SPU had no positive correlation with NDI scores (β=0.83, 95%CI= -0.07 to 1.73, P>0.05), while low back pain had a strong correlation with NDI scores (P<0.05).

Multivariate logistic regression model for CFI and NDI of the sample
In a multivariate logistic regression model, covariates were included as potential confounders in the nal models if they changed the estimates of NDI by more than 10% or were signi cantly associated with NDI, according to these protocols, as seen in Tables 1 and 2. Age, gender, working age, and low back pain were selected as covariates. After adjusting for age, working age, and sex covariates, CFI had a positive correlation with NDI scores (β=0.28, 95%CI=0.13 to 0.43, P<0.05), and after adjusting for low back pain CFI had a positive correlation with NDI scores (β=0.26, 95%CI=0.12 to 0.40, P<0.05). (See Table 3) Curve line correlation between the CFI and NDI of the sample Generalized additive models were used to visually assess the ToHTD and NDI relationships. We adjusted for age, sex, working age, and low back pain factors. The ToHTD had a curve line correlation with NDI -a monotone increasing relationship. (See Fig 2) Analysis of threshold saturation effect between the CFI and NDI of the sample As seen in Table 4, we performed threshold saturation effect analysis between CFI and NDI scores in participants. The logarithmic likelihood ratio test showed that there was a fold point (K=6) between CFI and NDI scores, and the differences were statistically signi cant (P<0.05). When CFI was less than 6 hours (K<6), the estimated change in NDI was 0.53, 95%CI was 0.26 to 0.81, and the differences were statistically signi cant (P<0.05). When CFI was greater than 6 hours (K>6), the estimated change in NDI was -0.03, 95%CI was -0.33 to 0.26, and the differences were not statistically signi cant (P>0.05). The logarithmic likelihood ratio test showed that this fold point was statistically signi cant (P<0.05).

Discussion
With recent rapid socioeconomic development, people are more mindful of their health. Increasingly more individuals who work in the o ce environment are seeking treatment for pain. In China, outpatients with CS are common in rehabilitation medicine, orthopedics, or traditional Chinese medicine. These patients often complain of neck and back pain, and have occasional complaints of dizziness, limb numbness, walking instability, perineal paresthesia, urinary and fecal incontinence, and sexual dysfunction. Such symptoms can have serious impacts on patients' lives and can result in a sharp decline in the quality of life. In a study conducted at the University Clinical Hospital in Olsztyn, Poland between 2011 and 2015, the most frequent MRI-diagnosed diseases were musculoskeletal diseases (58.0%), cervical disc disorders (12.5%), and spondylosis (4.6%). The authors concluded that the signi cant number of patients presenting with spinal disorders at young ages (31-40 years) pointed to the necessity of introducing methods in school-aged individuals to prevent disorders of the vertebral column [13]. In the present study, we also found that participants had a high incidence of neck pain syndrome (74.19% for males and 66.31% for females).
Previous research reported that most patients with CS were in occupations that required working longterm at a desk or work station, where it is common to remain for extended periods of time with the head tilted downward [14][15][16]. The cervical spine has seven vertebrae, and the joints formed by each vertebra are more exible. The anatomical features of the neck provide a large range of movement. Overloading the neck musculature can lead to cervical tissue damage. Holding the head in a lowered or exed posture maintains the neck muscles in a tensile state, which may cause muscle strain if the position is held over a long period of time. This forward exion posture may lead to static imbalance and accelerate degeneration of the intervertebral discs, small joints, and ligaments of the neck, eventually resulting in CS.
The NDI covers 10 dimensions of neck-speci c disability: pain intensity, personal care, lifting, reading, headache, concentration, work, driving, sleeping, and recreation [17]. This is closely correlated with cervical spine function [16], which can re ect neck pain intensity [18] , and can ultimately be used to evaluate the quality of life [19]. Feng et al. [20] analyzed survey data and found that among ultrasound technicians, lowering of the head for a long period of time led to rates of neck discomfort as high as 93.5%. Gremark Simenson et al. [21] found that the prevalence of CS among ultrasound technicians was 58%, and positively related to the length of time that the technician's head was held in a downward position while working. These results are consistent with those of our study. We found that CFI was positively correlated with the NDI regardless of unadjusted or adjusted covariates.
O ce workers should be mindful of CFI as much as possible. Our study found that there was a fold point (K=6) between CFI and NDI, and the differences were statistically signi cant (P<0.01). Many patients with CS have symptoms of neuropathy, however most symptoms are relatively benign and ultimately have a good prognosis [22]. The results of our study suggest that when CFI is greater than 6 hours, participants may adapt to neuropathy symptoms related to neck posture, leading to a decrease in symptoms. Even with this adaptation, cervical syndrome can persist. Therefore, we recommend that o ce workers limit CFI in order to decrease cervical syndrome.
In the 21st century, the rapid development of technology has resulted in the widespread use of electronic devices, leading to a near-universal presence of computers and smart phones in many countries, including China. One study found active arthritic changes caused by repetitive strain injury from excessive text messaging using smart phones [23]. Another study reported that smartphone use induced a more exed posture on the neck and trunk than other visual display terminal work [24]. Pain and fatigue worsened with longer smartphone use, and the authors suggested correct posture and breaks of at least 20 minutes when using smartphones [25]. Although our research found that using exed neck postures to use smart phones and for other activities had no effect on NDI scores, CFI was positively correlated with NDI. We suggest that o ce workers need to control CFI to reduce cervical symptoms when using smartphones or engaging in other activities that require exed postures for extended periods of time.
One limitation to our study was the lack of follow-up, therefore, the long-term results of our investigation were unknown. We did not analyze other risk factors associated with NDI such as mental stress, the time of day that people are working, working hours, work pressures, sleep quality, and nancial situation. In the future, we hope to conduct further studies and evidence-based research on CFI and NDI. Ethics approval and consent to participate: All participants lled out the questionnaire in anonymous way, the survey study need not approval by our Ethics Committee of hospital; informed consent was waived due to the nature of this survey study, which coincident with ethical requirements and waiver from the local research ethics committee.
Consent for publication: Not applicable.
Availability of data and materials: The datasets analyzed during the current study are available from the corresponding author on reasonable request.
Funding: This research received no speci c grant from any funding agency in the public, commercial, or not-for-pro t sectors.
Competing interests: The authors declare that they have no con ict of interest.    Graph depicting the association between CFI and NDI in participants.