INTRODUCTION
The incidence of musculoskeletal diseases in Korea has shown an increasing trend. According to statistics from the Health Insurance Review and Assessment Service [1], 17.91 million out of 51.39 million health insurance beneficiaries received hospital treatment for musculoskeletal diseases in 2019. This represents an increase of 7.9% compared to 2009, when the number of female patients was 9.84 million, 1.3 times the number of men. Among the musculoskeletal diseases over the 10-year period from 2009, the most frequent was ‘back pain’, accounting for a high percentage (30.1%). It mainly affects the spine and includes conditions such as cervical pain and low back pain. The increase in ‘back pain’ is associated with visual display terminal (VDT) syndrome, caused by the use of computers and smartphones.
Musculoskeletal disorders have been identified as a major health disability, particularly for women. A comprehensive literature review by NIOSH on “Musculoskeletal Disorders and Workplace Factors” found that women have a higher prevalence of musculoskeletal disorders than men [2]. Jeon et al. [3] reported that women accounted for 62.5% of the awareness rate of musculoskeletal disorders, higher than men at 46.5%, which is believed to be due to several physiological factors, such as differences in muscle strength and muscle fiber distribution, and body changes caused by pregnancy in women. Most call center workers are women who are sedentary during working hours, and physical factors such as long sitting time and neck flexion posture cause neck pain [4].
Awkward working posture is an important factor in the onset of musculoskeletal pain [5]. Forward head posture affects chronic primary headaches and various types of neck pain in adults [6,7]. Thoracic kyphosis may result in shoulder pain and decreased shoulder range of motion (ROM) and function [8]. Decreasing lower back curves are associated back pain, disc herniation, or degeneration [9]. Therefore, exercise experts consider postural problems as clinically important. Many experts have applied posture analysis and correction exercise programs into clinical practice.
Analysis of awkward spine posture is performed based on the sagittal plane. The most reliable method is X-ray analysis [10]. Posture is analyzed by assessing the alignment and angle of the spine using X-rays [11,12]. However, radiographic imaging can only be performed by doctors in a hospital setting. Radiation exposure poses a health risk that limits the number of safe measurements. Moreover, this assessment is not available in fitness centers, Pilates studios, and industrial sites.
A photograph-based posture analysis method assesses the relationship between body landmarks by taking a posture photo [13]. There is no risk of radiation exposure or health side effects and it is cost-effective because no special equipment or expensive devices are required. It can be easily implemented in clinical environments and can record natural postures in a subject’s daily life [14]. This method can be used by exercise experts and can be easily applied in general industrial sites. Therefore, it is widely used in fitness centers, Pilates studios, and health centers.
Magnetic analysis based on photography carries some disadvantages, as its reliability and validity can be reduced due to measurement errors, the subject’s posture, and the attachment of landmark points. However, many studies have shown that the posture photography analysis method is sufficiently reliable and valid compared to X-rays [15]. A study of 273 elementary school students who had their posture photographed three times from the front and side yielded satisfactory reliability results [16], and another study examining the sagittal posture of 766 adolescents confirmed a close correlation between radiographic images and photographic analysis [13]. A study that analyzed the reliability and validity of the craniovertebral angle (CVA) in sagittal posture, in sitting and standing positions, on pain-free subjects reported that post-based assessments were more reliable [17]. In a sagittal posture analysis study using videos of elderly and young people, a method for increasing reliability was proposed by capturing multiple photos and averaging the posture figures [18].
Photography-based posture analysis has also been developed clinically. Initially, posture was analyzed by taking pictures, uploading them into software, and drawing lines directly on body landmarks [19]. Now, it has developed into a method that automatically detects body landmark points using motion detection sensors and a program can even predict muscle tension according to the measured posture results and express it as an anatomical 3D image [20].
However, current research and clinical posture analysis tools analyze posture based on general body symmetry or inclination. The relationship between vertebral sagittal posture, musculoskeletal diseases, and pain remains difficult to observe in detail. A study has been conducted on posture analysis based on photographs of the sagittal plane according to age [18]; however, no studies have analyzed the relationship between sagittal spinal posture and pain in female workers. Therefore, the goal of this study was to identify the relationship between spinal posture and pain using sagittal plane photograph-based posture analysis and to provide a basis for the application of exercise programs to alleviate musculoskeletal pain.
METHODS
Participants
This study used the KOSHA CODE (H-30-2003) musculoskeletal disease survey, which was conducted among all female workers at Company H’s call center [21] and focused on cases presenting with pain lasting for more than one week and pain frequency of more than once a month in the previous year. Pain severity was classified into three groups according to the area affected and moderate or severe degrees of pain. A total of 16 workers with no pain (age 28.7 ± 3.7, body mass index (BMI) 16.20 ± 2.6), 17 workers with neck and shoulder pain (age 31.1 ± 4.5, BMI 16.8 ± 3.6), and 16 workers with low back pain (age 33.0 ± 4.4, BMI 18.0 ± 3.9) were included. Workers with disabilities caused by injuries, pregnant workers with a BMI of 25 or more, and workers who did not want to participate in the experiment were excluded. This study was approved by the Bioethics Review Board of the Catholic University of Korea (IRB) CUMC11U049.
Experimental Procedure
In a company conference room, all subjects underwent posture analysis using the same procedure. The participants wore well-fitted T-shirts, and videos were recorded using a digital camera (PL105, Samsung Electronics, Suwon). To reduce errors in the attachment points caused by the T-shirt, the fabric around the waist and ribs was pulled to the left as much as possible and fixed with a safety pin, ensuring its maximum proximity to the body. A grid with horizontal and vertical lines drawn at 10 cm intervals was installed at the back of the video recording. A backless chair (40 cm in height) was placed 20 cm from the center of the grid, and the height of the chair was adjusted using several small wooden boards such that the knees were at a 90° angle according to the height of the subject. The distance between the camera and the subject was 1.55 m, and the height of the camera was adjusted to 0.93 m when shooting a sitting posture using a tripod and 1.11 m when shooting a standing posture (Figure 1-a).
When photographing the sitting posture, the subject bent the heel between 30° and 45° with the hand lightly placed on the thigh (Figure 1-b). For the standing posture, the subjects were instructed to stand with both feet slightly narrower than the pelvis so that their feet did not stick to each other, and to stand with both arms lowered. At each position, the gaze was directed toward the front. Posture education was provided in advance to prevent intentional posture or bending. The participants were specifically asked not to take a slump or raised position on the back during video shooting. Moreover, the subjects were instructed to rest in their natural, comfortable posture without any tension. The video was recorded for 7 seconds in this state.
Measurements
Markers were attached to specific anatomical locations using 19 mm diameter stickers (10-C301, Leitech Korea, Seoul). The marker-labeling position was determined based on previous studies [15]. Through palpation, markers were applied to the right external auditory meatus, the midpoint between the right nose and mouth, the clavicle-sternal junction, the spinous process of thoracic vertebrae No. 1, thoracic vertebrae No. 3, thoracic vertebrae No. 11, lumbar vertebrae No. 1, the posterior iliac crest, and the anterior iliac crest. Once the markers were attached, the subject assumed a sitting posture and a standing posture facing the right wall from the camera position. To reduce errors, the marker position was reconfirmed and adjusted immediately before photographing. Using a video program (Gom Player, Gretek, Seoul), the captured video file was set to 50 frames per second for continuous storage, capturing approximately 7-8 images. A general image-editing program (Adobe Photoshop7.0, Adobe Systems, Inc., San Jose, CA) was used to measure the angle of each body part using the x- and y-axes of the captured images. To reduce the error caused by the subject’s movement during measurement, three images were randomly selected from the 7-8 images captured and averaged. Figure 2 illustrates the definition and measurement method for each angle. This method helps minimize errors that occur when subjects intentionally adopt different postures when only one picture is taken and it is based on prior research [18].
Statistical analysis
All analyses were performed using SPSS version 28.0 (SPSS Inc., Chicago, IL), and the mean and standard deviation of all angles were calculated. For the difference between the groups in each body angle, a one-way ANOVA test was used, and the Scheffé method was used for post hoc analysis. In addition, Pearson product-moment correla-tion coefficients were calculated to examine the correlation between angles. A significance level of 0.05 was set for all statistical tests.
RESULTS
Both the sitting and standing positions showed significant differences in several angles between the groups (Table 1). The difference in angles between each group in the sitting position showed significant differences regarding the neck slope angle (NS), upper cervical angle (UC), thoracic spine angle (TS), and lumbar spine angle (LS). Regarding NS, the neck and shoulder pain group had a significantly lower angle by 7.29° compared to the non-pain group, and the back pain group had a significantly lower by 9.21° compared to the non-pain group (p = .001). For UC, the neck and shoulder pain group had a significantly higher by 5.69º compared to the non-pain group (p = .017). In TS, the neck and shoulder pain group had a significantly higher angle by 4.87° compared to the non-pain group (p = .02). In LS, the low back pain group had a significantly higher angle by 4.75° compared to the non-pain group (p = .02). There were no significant differences between the groups in regards to the head tilt (HT), lower cervical (LC), and pelvic plane (PP) angles.
The difference in angles between each group in the standing position showed a significant difference in NS and TS. In NS, the neck and shoulder pain group had a significantly lower angle by 5.42° compared to the non-pain group, and the low back pain group had a significantly lower angle by 5.48 °compared to the non-pain group (p = .001). In TS, the neck and shoulder pain group had a significantly higher angle by 5.68° compared to the non-pain group (p = .02). There were no significant differences between the groups for the other angles (HT, UC, LC, LS, or PP).
A significant correlation was observed between the angles in the sitting and standing positions (Figure 3). HT was positively correlated with UC in the sitting position (r = 0.636, p = .001). NS was negatively correlated with UC (r = -0.56, p = .001), TS (r = -0.43, p = .002), LS (r = -0.42, p = .002), and PP (r = -0.37, p = .007), and positively correlated with LC (r = 0.28, p = .047). UC was positively correlated with LS (r = 0.31, p = .02). LS was positively correlated with PP (r = 0.33, p = .02).
In the standing posture, HT was positively correlated with UC (r = 0.78, p = 0.001), TS (r = -0.3, p = .037), and PP (r = -0.48, p = .001). NS was negatively correlated with UC (r = -0.35, p = .001), TS (r = -0.43, p = .002), and LC (r = 0.32, p = .003). UC was negatively correlated with PP (r = -0.43, p = .002). LC was positively correlated with TS (r = -0.28, p = .05). TS was negatively correlated with LS (r = -0.47, p = .001).
DISCUSSION
Chronic neck and low back pain is a musculoskeletal disease that is a trend in modern society, with the proportion of patients increasing, especially in due to VDT and sedentary work [1]. Musculoskeletal diseases occur more frequently in female workers than male workers [2]. Physiologically, women undergo several changes compared with men, such as changes in muscle mass, other muscle fiber distributions, and body changes due to pregnancy [3]. Most call center workers are female and endure long-term sedentary work in a VDT environment, frequently adopting forward head postures to view the display [4].
Awkward posture is one of the main causes of pain [5]. Maintaining an awkward posture with a severe imbalance in muscle strength for a long time causes tension between the muscles and joints, which leads to a decrease in flexibility, movement limitation, and pain [13]. As the need to correct posture-related pain has increased, studies have been conducted on methods that can easily and simply measure and correct postural deformation in clinical settings. According to Kendall et al., the most widely known method for evaluating posture is the pendulum and the midline analysis method [22]. Based on this method, the ideal posture is defined as the alignment where the center of the ear canal and shoulder, hip joint, center of the knee, and ankle joint coincide with the midline. Recently, some companies (e.g., Biotonix and PosturePro) have developed computer-based posture analysis systems based on medial line analysis for the development of exercise programs and clinical treatments to relieve back pain [23]. However, these programs have difficulty analyzing the spine’s posture in detail.
Therefore, we used a video-based posture analysis method [18], which allows for simple photography and detailed observation of posture on the sagittal plane. The video analysis method helps to compensate for errors caused by intentionally adopting different postures. By capturing a video for several seconds, it is possible to obtain various postural image data through frame capture, and then calculating the average value. Furthermore, an image editing program that is readily available in the market was also used. Therefore, we aimed to present a posture analysis method that can be easily applied, without time, place, and cost constraints, and to provide basic data for exercise programs to prevent musculoskeletal diseases by grasping the relationship between pain and posture.
According to our results, NS was lower in the neck and low back pain group than in the non-pain group in both the sitting and standing positions. This result is consistent with previous studies showing that the CVA has a strong negative correlation with neck pain [6]. The significance of the results of this study is that NS was also lower in the low back pain group. NS refers to the anterior movement of the head, which is explained by the anterior movement of the center of gravity. This posture shortens the muscle fibers around the joint and excessively increases the muscles around the joint, causing chronic neck pain [24]. Musculoskeletal abnormalities such as neck pain affect the balance of the body, making it impossible to maintain normal body alignment [25], and Posture imbalance caused by bad posture causes pelvic distortion and asymmetry of the trunk muscles, increasing muscle and spinal loads, and worsening back pain [26]. Therefore, NS can be used as an important indicator of neck and back pain in all groups.
NS indicates how straight the neck is when standing on a horizontal line. The decrease in NS occurs because of the combination of the flexion of the lower cervical spine and extension of the upper cervical spine [27]. Therefore, to increase this angle, it is necessary to help workers in pain with the simultaneous stretching motion of the lower cervical spine and the flexion motion of the upper cervical spine. In fact, a previous study showed that performing such cervical stabilization exercises in patients with chronic cervical pain resulted in a significant reduction of the Visual Analog Scale compared to the normal group [28].
In the neck and shoulder pain group, in the sitting position, UC and TS were significantly higher than those of the non-pain group, and these two angles were found to have a negative correlation with NS. Therefore, it is necessary to implement an exercise program that includes lower cervical extension muscle strengthening exercises to increase NS and lower UC, upper cervical flexor muscle strengthening exercises, and upper back extension exercises to lower TS for workers with neck and shoulder pain. Previous studies have suggested that kyphotic postures and neck pain are strongly correlated in young adult subjects and that therapeutic exercise may change the cobbs angle and neck pain in kyphotic patients [29].
In this study, we found that LS, PP, and NS were significantly negatively correlated in the sitting position. This was different from the result of no significant correlation between LS, PP, and NS in a previous study [18]. In this study, elderly individuals were not included, which seems to result in difference in stiffness according to age. Lumbopelvic posture may affect neck posture in adults who are not the elderly. Therefore, in addition to direct corrective exercises for neck and shoulder pain complainants, proper posture education to adjust pelvic and low back neutrality is also necessary.
In the low back pain group, LS was 4.75° higher than that in the non-pain group in the sitting position. High LS indicated lumbar flexion. A study on sagittal alignment analysis of the normal spine and a study comparing lumbar puncture angles in healthy people and patients with low back pain also found that lumbar spine alignment was closely related to low back pain [30,31]. Inefficient muscle stability in the lumbar spine was also closely related to low back pain [32]. In addition, in terms of the relationship between the lumbar curve and pain in patients with low back pain, hypolordosis of the lumbar spine was associated with pain [33] and a decrease in the lumbar curvature was associated with low back pain [34]. The decrease in lumbar curvature puts stress on the structure of the spine, and to reduce this stress, it is necessary to increase the lumbar curvature through lumbar stabilization exercises [35]. Therefore, it is important to protect the spine from stress by strengthening the lumbar muscles [36]. A study to observe whether pain is reduced by applying a posture education program that can lower LS during work along with lumbar deep muscle stabilization exercises in workers with back pain is needed.
It was shown that LS was negatively correlated with PP in the sitting position. The correct alignment of the pelvis when seated is achieved when the anterior superior iliac spine (ASIS) and the posterior superior iliac spine (PSIS) are aligned horizontally, and the left and right ischial spine rests neatly on the floor of the chair. This alignment of the pelvis straightens the spine and provides stability, facilitating the movement of the upper limbs [37]. Therefore, not only the curve of the lumbar spine but also the alignment of the pelvis should be considered in the sitting position for workers with back pain.
In addition, LS was found to have a negative correlation with NS and a positive correlation with UC in the sitting position (Figure 3), which implies that LS can be affected by the forward head posture with the head leaning forward toward the object of work, such as a monitor or document. Therefore, it is necessary to prevent the reduction of NS by applying an appropriate exercise program for back pain and by improving the ergonomic environment for the height and location of the object of work and the distance between the object of work and the worker.
In the standing position, the neck and shoulder pain group, along with a higher NS, also had a higher TS of 5.86 degrees than the non-pain group, indicating that the degree of thoracic kyphosis in the standing position is related to neck and shoulder pain.
There are two types of exercise programs for posture correction, according to the order of correction. There are “top-down” methods, which are corrections from head to foot, and “bottom-up” methods, which are corrections from foot to head17. In this study, NS correlated with five different angles in the sitting and standing positions. Based on this, when planning a posture correction exercise program, the “top-down” method, in which the neck exercise is performed first and the rest of the relevant back, waist, and pelvis exercises are performed in order, is estimated to be more effective.
This study was conducted only on women who performed their work sitting down, and the results cannot be generalized due to a small sample size. In addition, there is a limitation in the research methods that can introduce errors, such as the attachment of stickers, as the experiment was conducted in the workplace and the participants were wearing regular clothes. Another limitation is that not all factors that may cause pain, such as mental and social relationships, were considered; only physiological pain was considered. Finally, the study was not conducted in a working environment where workers controlled the posture analysis conditions.
However, it is a meaningful attempt to investigate the relationship between pain and posture in female workers. It can be said that it lays the foundation for future research related to posture by using a new research method called posture analysis through sagittal plane video shooting, which has not been used in domestic research. In the future, more advanced research related to pain is needed to develop and apply an exercise program based on the results of the present study. Specifically, we compared the top-down correction method, which observes the effects of neck posture correction exercises on lower back and pelvic pain, with the bottom-up method, which observes the effects of lower back and pelvic posture correction exercises on neck and shoulder pain.
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