The impact of saddle chairs on spinal curvatures

1 Introduction

Today, more than 75% of all employees work in a sitting position [1]. According to some authors, an incorrect sitting posture increases spinal muscle tension and load on intervertebral discs, accelerating the occurrence of degenerative changes in the disc and joints can lead to low back pain among office workers [2, 3]. Long-term, incorrect sitting and a lack of physical activity lead to a reduction in the strength and endurance of the spinal muscles and ligaments. This may be one of the causes of low back pain [4–6]. Low back pain is the most frequent cause of visits to the family doctor [7, 8]. That is why finding the appropriate chair that ensures proper curvatures of the spine could help diminish low back pain risk factors and reduce recurrent episodes ofpain.

2 Objective

The aim of the study was to determine the impact of an adjustable saddle chair compared to an adjustable office chair with a backrest on sitting posture.

3 Methods

Ethics approval for the study was obtained from the university ethics committee.

3.3 Procedure

The analysis employed the photogrammetric method, based on the phenomenon of the projection chamber and Moiré projection [9]. Moiré fringes is a visual pattern generated by two added images. Such pattern is used to measure the shape of complex objects in one shot imaging. The object might be even as complex as a human body with its non-regularity and many curvatures. This technique greatly shortens 2D measurement of many parameters and gives very good resolution and acceptable accuracy. Its great advantage is also moderate investment in the equipment, it means cost effectiveness.

One image usually consists of a regular pattern, a graphic shape e.g. vertical black lines at same distance on a transparent background. Such image is projected as a slide onto the interested object e.g. a patient’s back, which is under investigation. The shape of the patient’s back changes the regularity of the lines, deforms their straightness. This change brings the information about the back curvature. The image of the illuminated back is recorded by the camera. In the next step the first image (the regular pattern) and the second one are added in the computer: they are simply superimposed, overlaid one over another. This summation image shows the Moire fringes that can be easily analyzed on the computer.

Nowadays the regular pattern is generated by the computer, which also controls the projector and the recording camera. The computer contains the entire software: to control the devices, to acquire the images and to analyze them.

Before the measurements were taken, the participants were told how the examination would be conducted, and they agreed to participate. The procedure of informed consent included an explanation of the purposes of the research, a description of the expected duration, a description of the procedures, and information regarding the benefits (clinical and imaging evaluation of the posture), and were told that there was no risk.

The instruction session was then conducted by a physiotherapist on the correct position of the spine. Correct posture indicates proper alignment of the body’s segments so that the least amount of energy is required to maintain a desired position, and spinal curvatures are neutral and balanced. The benefit of achieving this ideal position is that the least amount of stress is placed on the body’s tissues. Participants were seated for 5 minutes to hear the instructions given by the physiotherapist. Then they undressed, and while standing, anatomic points were marked on their back (scapular lower angles, all spinous processes from C7 to S1, and the posterior superior iliac spines). The procedure of marking the anatomical points lasted around 5 minutes and was conducted by an experienced physiotherapist to ensure that the examination was reliable. After determining the anatomic points, in a pre-determined, correct sitting position, a photogrammetric image was taken [10]. Then, further processing of the pictures took place without the participation of the testedpersons.

To analyze the results, the selected points on the body of each subject were used. An example of a photogrammetric test is shown in Fig. 1. Figure 1 is an image of the back of an examined person with a contour map based on the Moiré phenomenon. The figure shows the degree of rotation of selected vertebrae. The graph on the right shows the level of rotation in degrees.

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Fig.1

View of the spine with Moiré projection.

The first photo was taken while the participants were in a seated position on an adjustable chair, hips angled 90 [°] in relation to the trunk, lower legs in a perpendicular position in relation to the thighs, feet resting on the floor. Participants were seated symmetrically with the pelvis on the chair. The second picture was taken while the participant sat on a saddle chair with adjustable height, without a backrest or armrests, and the participant assumed the corrected posture.

The biometric parameters of study group are presented in Table 1.

The parameters of the corrected posture while sitting on an office chair and on a saddle chair showed statistically significant differences for the GAMMA angles, the angles of the trunk inclination (KPT), the depth from the top of the thoracic kyphosis to the thoracolumbar transition (GKP), and the depth of lumbar lordosis (GLL). A summary of the results of the measurements in both positions is shown in Table 3.

A statistical analysis was conducted using a Wilcoxon matched pairs test that confirmed a statistically significant difference between the values of KPT and GLL in the position on an office chair and on a saddle chair, as well as the presence of statistically significant differences at between the values of GAMMA and GKP on both chairs. It was shown that there is a statistically significant difference at p < 0.05 (p = 0.0189) between the values of GAMMA in two consecutive measurements in the position on an office chair and on a saddle chair. Higher values of this parameter were recorded in the position on a saddle chair (33.3 sd. 22.0), whereas lower values were noted for the position on an office chair (26.4 sd. 22.2). It means that on a saddle chair head protraction was greater compared to an office chair, which is a unfavorable situation.

It was confirmed that there was a statistically significant difference (p = 0.0079) between the values of KPT in two consecutive measurements in sitting on an office chair and on a saddle chair. Higher values were recorded for the position on an office chair (–4.8 sd. 18.2), whereas lower values were noted for sitting on a saddle chair (–12.3 sd. 15.2). Deviation from the vertical of the line C7-S1 in the sagittal plane- torso forward flexion (negative trend) was larger while sitting on the office chair.

It was shown that there was a statistically significant difference (p = 0.0493) between the values of GKP in two consecutive measurements in the position on an office chair and on a saddle chair. Higher values of this parameter (flattening of thoracic kyphosis) were recorded for sitting on an office chair (0.8 sd. 8.7), whereas lower values were noted for sitting on a saddle chair (–1.3 sd. 10.1).

There was a statistically significant difference (p = 0.0024) between the values of GLL for sitting on an office chair and on a saddle chair. Higher values (deeper lumbar lordosis) of this parameter were recorded for the saddle chair (1.5 sd. 6.2) compared to the office chair (–0.2 sd. 6.0).

The issues related to the shape of spinal curvatures are often discussed in the literature, due to the prevalence of LBP in the population worldwide. According to Adams, structural disc pathology can be created in cadaveric specimens by severe or repetitive mechanical loading, with a combination of bending and compression being particularly harmful to the spine [6]. Also, an abnormal range of motion into flexion or extension leads to more stress on the facet joints and their degeneration [11]. Interesting research regarding the importance of proper spine ergonomics education was conducted by Czaprowski et al. The authors study the changes in spine curvatures in children and adults after hearing the command, “straighten up” [12]. In the standing position, a reduction in both upper and lower kyphosis as well as in lumbar lordosis was noted for the whole group of children. It was concluded that the optimal position for sitting is the one involving a lordotic position in the lumbar spine. However, correction after the command, “straighten up”, does not result in such a sitting position. Most often, the examined subjects assumed the position with elongated lordosis [12]. To prevent improper sitting postures – risk factors for low back pain – it is necessary to demonstrate and teach patients the desired posture during physiotherapy.

The importance of proper curvatures in a working position was confirmed by Lisinski [13]. The setting of the sacrum may also influence the size of the curvatures in a sitting position. Studies have shown that women for whom the position of the sacrum resulted in a reduction of lumbar lordosis while sitting, felt LBP after a shorter time than in a standing position. In women performing work while standing, for whom the inclination of the sacrum had correct values, back pain appeared later than in women whose work involved a sitting position. If the inclination of the sacrum was incorrect, these women felt discomfort during the test earlier than during work performed in a sitting position. Among men with normal inclination of the sacrum, pain appeared in a sitting position later than for a comparable group of women. The explanation for this may be less trunk muscle strength in women, which causes them to fatigue faster. On the other hand, for men who work while standing, pain experienced at normal values of the inclination of the sacrum occurred earlier than for women [13]. Sitting on the saddle chair led to better position of pelvis in inclination leading to correct lumbar lordosis. That position might be favorable for patients with decreased sacrum inclination.

Research on the correct posture was conducted with electromyography by Castanharoet et al. [14]. The authors found that normal lordosis leads to minimizing the tension of passive structures surrounding the spine, and the position of the pelvis and the sacrum was closest to the optimal in neutral position. In turn, the flat back position activates erector spinae muscles, which leads toan additional load on the lumbar spine [14]. In our study, it was determined that a saddle chair increased the depth of lumbar lordosis (parameter GLL), which can prevent back pain in the course of lumbar disc disease.

Office chairs are designed for the employee to be in an ergonomic position. The studies of Annetts et al. compared four types of chairs: a kneeling chair, a saddle chair, a swivel chair and a standard office chair. Sitting positions on various chairs differed significantly. A swivel chair and a standard office chair caused a decrease in the depth of the lumbar lordosis. The authors concluded that sitting on a saddle chair could be considered as the nearly perfect posture concerning the lumbar spine [15]. The importance of maintaining the lumbar lordosis and optimal muscle activity was stated by O’Sullivan et al. [16]. They compared a Back App type of a chair and a standard chair without a backrest. The results showed that the activity of the lumbar muscle was higher for a standard chair. The authors believe that the reduced muscle activity while sitting on Back App is associated with decreased bending in the hip joints, as well as a slight inclination of the trunk. It was concluded that maintaining a neutral posture in the lumbar spine with optimal muscle activity is beneficial during prolonged sitting [16]. These results confirmed the authors’own findings.

Muscle activity in different situations was measured in a study conducted by Mörland Bradl. The use of EMG confirmed the correct activity of the multifidus and the longissimus dorsi during gait [17]. In turn, in the sitting position, when there was a flattening of lumbar lordosis, the activity of the multifidus and the longissimus dorsi declined sharply [1]. The load exerted on the spine in a sitting position is high and the muscle activity is negligible, so the entire load is transmitted through the passive structures such as ligaments and intervertebral discs. The authors concluded that the muscle activity does not depend on the type of chair, but on the nature of the office work. In order to naturally activate the paraspinal muscles, one needs to have breaks for walks and other activities in a standing position [17]. In line with the above findings, Gadge and Innes presented their results concerning the use of an adjustable saddle chair with a backrest. It was found that a standard office chair caused greater discomfort compared to a saddle chair [18]. Wang used a rehabilitation chair as part of the rehabilitation program for patients with LBP. The study group used chairs designed to correct the posture, and the control group used traditional office chairs. After six months, the pain experienced by the participants in the study group decreased significantly [19]. Improving body posture reduces the incidence of back pain [20]. According to authors study saddle chair might also have positive affect in preventing and treating low back pain.

However, posture re-education exercises require time and commitment from the patient. That is why physiotherapists are constantly seeking other ways to support long-term maintenance of proper body posture. One alternative is to find the most optimal chair for the spine position [21]. One should not forget that the sitting posture is a common aggravating factor for pain both at the cervical and lumbar spinal regions [22–25].

It is worth mentioning that LBP may by caused by different pathology. Patients with spinal stenosis will benefit from sitting in a flexed position, and encouraging them to maintain an erect posture will elevate their symptoms [26]. On the other hand, patients with disc herniation will benefit from maintaining lumbar lordosis. Therefore, it is important to individually set up a working chair.

Sitting on the saddle chair had a negative influence on head and cervical spine. Head protraction increased significantly and it has already been proposed/shown by Przybyla et al. as a risk factor for cervical pain, as the neck is relatively vulnerable in bending [27].

As shown by our research and the studies of other authors, a saddle chair may be an example of a chair that, through beneficial effect on lumbar lordosis, can be used as a means of prophylactic of discogenic LBP. The physiotherapeutic goals of optimizing sitting habits are not only logical, but also absolutely essential, considering the large amount of time that is spent sitting in modern society[28].

6 Conclusions

An increase in the depth of lumbar lordosis was observed for sitting on saddle chairs. Sitting on a saddle chair resulted in a significant increase in the protraction of the cervical spine.

Conflict of interest

None to report.