Abstract
[Purpose] The study aimed to determine the relationship between low back pain and lumbar and hip movement in desk workers with chronic non-specific low back pain, in order to obtain basic data regarding measures for preventing low back pain in desk workers. [Participants and Methods] The study included 10 desk workers (all female, age: 47.1 ± 6.0 years). The following measurements were recorded: numerical rating scale score for pain assessment at the time of maximum forward and backward bending of the trunk while standing, and the amount of movement of the trunk and the lumbar and hip joint. The ratio of the lumbar and hip joint movements during maximum forward and backward bending of the trunk was calculated. [Results] For maximum forward and backward bending of the trunk, a positive correlation between the numerical rating scale score and the ratio of movement for the lumbar and a negative correlation with that of the hip joint were noted. [Conclusion] Moving the hip joint while suppressing excessive lumbar movement is one of the measures for preventing low back pain in desk workers.
Key words: Desk workers, Non-specific low back pain, Ratio of movements
INTRODUCTION
It is estimated that 70–80% of the world’s population will experience low back pain at least once, of which 85% is nonspecific low back pain1, 2). Non-specific low back pain has been reported to have no apparent cause2) and does not correlate with findings on an X-ray or nuclear magnetic resonance imaging with clinical symptoms3). It is believed that exacerbation of back pain leads to a decrease in productivity due to difficulties in employment and has a significant socio-economic impact4). Among workers, those who spend 80% of their working hours in a sitting position are defined as desk workers (DWs)5), and DWs are said to be more likely to develop low back pain due to their prolonged sitting posture6, 7). In recent years, it has been reported that the prevalence of low back pain in DWs has increased with the development of Information Technology equipment8). Therefore, the prevention of low back pain in DWs is an important socio-economic issue.
To evaluate low back pain, the amount of lumbar and hip joint movements during maximum forward and backward bending of the trunk in the standing position are often evaluated9,10,11). A characteristic of the movement of people with low back pain is the increased ratio of lumbar movement to the ratio of hip joint movement in maximum forward and backward bending of the trunk in the standing position9, 11, 12). Therefore, one of the factors for the appearance of lower back pain was considered to be the influence of hypermobility of the lumbar during trunk movement.
In the sitting posture with the trunk flexed, it has been reported that flexion relaxation phenomenon appears in the erector spinae13), and support of the lumbar is secured by soft tissues such as the posterior spinal ligament14). In other words, the sitting posture of DWs is thought to be maintained for a long time owing to the stiffness of non-contracted tissues such as ligaments. It is assumed that the sustained elongation load on the non-contracted tissue increases the ratio of lumbar movement during trunk movement, which may lead to low back pain. In addition, it has been reported that hip joint movement is closely related to the lumbar movement15, 16), and that low back pain is associated with excessive mobility of the lumbar as well as decreased mobility of the hip joint17). Therefore, it is possible that the lumbar pelvic rhythm is imbalanced even in DWs with low back pain. However, there are no reports on the relationship between low back pain and the ratio of lumbar and hip joint movements during maximum forward and backward bending of the trunk in the standing position in DWs. If the relationship between low back pain, lumbar, and hip movements during trunk movement is determined, it may help in considering measures to prevent back pain in DWs with low back pain. The aim of this study was to determine the relationship between low back pain, lumbar, and hip movements in DWs with chronic non-specific low back pain to obtain basic data for measures to prevent low back pain in DWs.
PARTICIPANTS AND METHODS
The participants were 10 DWs with chronic nonspecific low back pain (all female, age: 47.1 ± 6.0 years, height: 158.4 ± 5.5 cm, weight: 55.0 ± 6.1 kg). The contribution of hip range of motion during trunk movement is higher in female than in male18). Since hip joint movement is associated with lumbar movement15, 16), then low back pain is more likely to be related to trunk movements as females were selected for this study. Females were also selected to unify the participants. The participants did not have any specific orthopedic diseases of the lumbar and hip joint caused by low back pain and did not have any apparent limitation in the range of motion of the hip joint (flexion angle: 120 ± 3.3°, extension angle: 14 ± 3.9°). The criteria for chronic low back pain in this study were those with chronic low back pain for more than 12 weeks19, 20). DWs were defined as workers who spend 80% of their working hours in the seated position5). As for ethical considerations, this study was explained and written consent was obtained from all participants. The study was approved by the Ethics Committee of the Nanto Home Visit Nursing Station (approval number: 2019.NHS.3).
The study design was cross-sectional. The task was to measure the maximum forward and backward bending of the trunk in a standing position, at which time photographs and video filming were taken. Also, the inertial sensor tilt angle (TSND151, ATR-Promotions, Kyoto, Japan) was measured. Reflection markers for photographic and video filming were placed at six locations: the seventh cervical vertebrae, the right anterior superior iliac spine (ASIS), the right posterior superior iliac spine (PSIS), the third sacral vertebrae, the right greater trochanter, and the right epicondylus lateralis ossis femoris (Fig. 1). An inertial sensor was installed at the third lumbar vertebrae and set up in the acceleration range of 8G, an angular velocity range of ± 1,000 dps, a sampling interval of 10 ms, and an average number of 1 of samples using the receiving software (Sensor Controller, ATR-Promotions, Kyoto, Japan). A digital video camera (HDC-TM45, Panasonic Corporation, Kadoma, Japan) was set up 3 m to the right side of the participants.
Fig. 1.
Location of reflection markers and inertial sensor.
1: Third lumbar vertebrae (inertial sensor).
2: Right anterior superior iliac spine (reflection marker).
3: Right posterior superior iliac spine (reflection marker).
4: Third sacral vertebrae (reflection marker).
5: Right greater trochanter (reflection marker).
6: Right epicondylus lateralis ossis femoris (reflection marker).
7: Seventh cervical vertebrae (reflection marker).
The video recording was performed during the task, and photographs were taken at rest standing positions and during maximum forward and backward bending of the trunk. Before the task, the participants were tasked with the measurement task, following which they practiced the forward and backward bending of the trunk in the standing position one for each. Measurements were performed at rest standing for 2 sec, followed by forward bending of the trunk, and held in the final position for 2 sec. After that, the participants returned to rest standing and held rest standing for 2 sec. The participants performed this forward and backward bending of the trunk twice. For the measurements, inertial sensors and video recordings were synchronized. Numerical Rating Scale (NRS)21) was used as an index of the intensity of low back pain during maximum forward and backward bending of the trunk, and interviewed the participants after each trial. The NRS was used as a self-rating system for pain, which requires a pain score on a scale of 11 from 0 to 10, with 0 being no pain and 10 being the worst pain imaginable21). The NRS has been used as an index of the intensity of low back pain22, 23) and also validated and reliable21, 24). Therefore, the NRS was used as an index of the intensity of low back pain in this study.
For the data analysis, the image analysis software Image J25) was used to calculate the amount of trunk and hip joint movements during maximum forward and backward bending of the trunk in the standing position based on the reflection markers (Fig. 2). The amount of trunk movement was determined as the difference between the trunk tilt angle in the rest standing (the angle at which the line connecting the seventh cervical vertebrae and the third sacral vertebrae intersects the perpendicular line from the floor, hereafter referred to as the trunk tilt angle), while trunk tilt angle was determined during maximum forward and backward bending of the trunk (Fig. 2). The amount of hip joint movement was defined as the difference between pelvic tilt angle at rest standing (the angle at which the line connecting the ASIS and PSIS intersects the line connecting the right greater trochanter and right epicondylus lateralis ossis femoris, hereafter referred to as pelvic tilt angle) and pelvic tilt angle during maximum forward and backward bending of the trunk (Fig. 2). The amount of trunk and hip joint movements were calculated from the mean values of the two trials, respectively. This value was then used as the representative value for each task. Inertial sensor tilt angle was set as the difference between maximum forward and backward bending of the trunk and rest standing. Inertial sensor tilt angle was calculated as the average angle for each 2 sec during the rest standing and maximum forward and backward bending of the trunk. The mean of the two trials in each task was then used as a representative value. The amount of lumbar movement was the difference between the amount of inertial sensor tilt angle and the amount of hip joint movement during maximum forward and backward bending of the trunk. The ratio of the lumbar and hip joint movements to the amount of trunk movement (the amount of lumbar and hip joint movements / the amount of movement of trunk ×100) was calculated. This value was then used as the ratio of the lumbar and hip joint movements during maximum forward and backward bending of the trunk. The NRS was defined as the mean of the 2 trials during maximum forward and backward bending of the trunk as representative values for each task.
Fig. 2.
Each baseline and the amount of movement in each region.
1: Perpendicular lines from the floor.
2: Line connecting the seventh cervical vertebrae and third sacral vertebrae.
3: Line connecting the right greater trochanter and right epicondylus lateralis ossis femoris.
4: Line connecting the ASIS (right anterior superior iliac spine) and PSIS (right posterior superior iliac spine).
5: Inertial sensor tilt lines.
(1): Trunk tilt angle in rest standing.
(1)´: Trunk tilt angle in maximum bending position.
(2): Pelvic tilt angle in rest standing.
(2)´: Pelvic tilt angle in maximum bending position.
(3): Angle between the inertial sensor tilt angle and the perpendicular line from the floor in rest standing.
(3)´: Angle between the inertial sensor tilt angle and the perpendicular line from the floor in maximum bending position.
| (1)−(1)´ |: The amount of trunk movement.
| (2)−(2)´ |: The amount of hip joint movement.
| (3)−(3)´ | −| (2)−(2)´ |: The amount of lumbar movement.
(| (3)−(3)´ | −| (2)−(2)´ |) / | (1)−(1)´ | ×100: The ratio of the lumbar movement.
(| (2)−(2)´ | / | (1)−(1)´ |)×100: The ratio of the hip joint movement.
Statistical analysis was performed using EZR (Easy R, Saitama Medical Center, Jichi Medical University, Saitama, Japan)26). The median (interquartile range) of each value was calculated after testing the normality of the NRS and ratio of the lumbar and hip joint movements during maximum forward and backward bending of the trunk using the Shapiro-Wilk normality test. Following this, the relationship between the NRS, ratio of the lumbar and hip joint movements during forward and backward bending of the trunk was assessed using the Spearman’s rank correlation coefficient. The level of significance was set at 0.05.
RESULTS
NRS and the amount of lumbar and hip joint movements during maximum forward and backward bending of the trunk are shown in Table 1. The NRS during maximal forward and backward bending of the trunk was comparable. During maximal forward bending of the trunk, ratio of the hip joint movement tended to be greater than the ratio of lumbar movement. During maximal backward bending of the trunk, the ratio of the lumbar movement tended to be greater than the ratio of hip joint movement.
Table 1. NRS and the ratios of lumbar and hip joint movements during maximum forward and backward bending of the trunk.
| Maximum forward bending of the trunk | Maximum backward bending of the trunk | |
| NRS | 3 (2.3–4.8) | 3 (2.3–4.8) |
| The ratio of lumbar movement (%) | 31.8 (14.0–34.2) | 72.9 (61.0–83.8) |
| The ratio of hip joint movement (%) | 56.3 (42.5–58.2) | 36.7 (27.0–57.6) |
Values are expressed as median (interquartile range).
NRS: Numerical Rating Scale (0: no pain, 10: maximum pain).
Table 2 shows the relationship between the NRS, ratio of the lumbar, and hip joint movements during maximum forward and backward bending of the trunk. A positive correlation (rs=0.76, p=0.01) was found between NRS and ratio of lumbar movement, and a negative correlation (rs=−0.66, p=0.04) was found between the NRS and ratio of hip joint movement during maximum forward bending of the trunk. A positive correlation (rs=0.65, p=0.04) was found between the NRS and ratio of lumbar movement, and a negative correlation (rs=−0.65, p=0.04) was found between the NRS and ratio of hip joint movement during maximum backward bending of the trunk.
Table 2. Correlation coefficients between NRS, and the ratio of lumbar and hip joint movements during maximum forward and backward bending of the trunk.
| Ratio of lumbar movement | Ratio of hip joint movement | |
| NRS in maximum forward bending of the trunk | 0.76* | −0.66* |
| NRS in maximum backward bending of the trunk | 0.65* | −0.65* |
*: Correlation with NRS (p<0.05).
NRS: Numerical Rating Scale (0: no pain, 10: maximum pain).
DISCUSSION
In this study, the relationship between low back pain, lumbar, and the hip joint movements of DWs with chronic non-specific low back pain was examined. The results of this study showed a positive correlation between low back pain and the ratio of lumbar movement and a negative correlation between low back pain and ratio of hip joint movement during maximum forward and backward bending of the trunk. It has been reported that chronic nonspecific low back pain is, in part, due to the structural vulnerability of the lumbar region27), and that sustained load from habitual exercise patterns in daily life can lead to tissue micro-instability28). It has also been reported that sitting with the trunk flexed for a long period of time causes thinning of the lumbar soft tissues due to gradual elongation of lumbar soft tissues, which impairs the stability of the spine support mechanism29) and decreases the rigidity of the lumbar spine in the anteroposterior direction30). It is said that excessive mobility of the lumbar spine stimulates the pain receptors and causes low back pain31). It has also been reported that hip joint movement is closely related to lumbar movement15, 16) and that low back pain is associated with excessive mobility of the lumbar as well as decreased mobility of the hip joint17). During trunk exercise, a decrease in the amount of hip joint movement during maximum forward bending of the trunk was caused by excessive mobility of the lumbar spine due to low back pain32). In the present study, participants with strong low back pain may have been less stable in the lumbar spine due to thinning and micro-instability of the lumbar soft tissue compared to those with weakness. As a result, it is thought that participants with strong low back pain move excessively in the lumbar during maximum forward and backward bending of the trunk, and the hip joint movement is relatively small. However, in the present study, it was not possible to determine whether the excessive mobility of the lumbar and the decreased mobility of the hip joint were caused by low back pain, or whether the low back pain was caused by the excessive mobility of the lumbar and the decreased mobility of the hip joint. Therefore, it is necessary to examine the causal relationship between low back pain and excessive mobility of the lumbar or decreased mobility of the hip joint in the future.
The first limitation of this study was the small number of participants (n=10). Therefore, it is necessary to increase the number of participants in the future to investigate the relationship between low back pain and the ratio of lumbar or hip joint movements in DWs. Second, only the final positions of the forward and backward bending of the trunk were measured. Therefore, it is necessary to examine the relationship between the ratio of lumbar and hip joint movements and low back pain and muscle activity during the course of exercise such as trunk forward bending every 20°. Finally, only one camera was used in this study, so only the posture of the sagittal plane was analyzed. It is necessary to examine the relationship between low back pain and the ratio of lumbar and hip joint movements in the frontal and horizontal planes using a three-dimensional motion analysis system.
In conclusion, the aim of this study was to determine the relationship between low back pain, lumbar, and the hip movements in DWs with chronic non-specific low back pain to obtain basic data for measures to prevent low back pain in DWs. The results of the present study showed that low back pain was related to the ratio of the lumbar and hip joint movements during maximum forward and backward bending of the trunk as a characteristic of trunk movements in the standing position in DWs with low back pain. It is also considered important to move the hip joint while suppressing excessive lumbar movement as one of the measures to prevent back pain in DWs. In the future, the number of participants to examine the characteristics of trunk movements in DWs with low back pain has to be increased.
Funding
This work was supported by JSPS KAKENHI grant number JP19K24181.
Conflicts of interest
The authors declare no conflicts of interest.
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