Association of low back pain with muscle stiffness and muscle mass of the lumbar back muscles, and sagittal spinal alignment in young and middle-aged medical workers
Introduction
The occurrence rate of low back pain (LBP) within the lifetime of adults is about 80% (Waddell, 1987). LBP is induced by stress on the structures around the lumbar spine, such as intervertebral disks, intervertebral joints, ligaments, nerves, and lumbar back muscles. Thus, clarification of the cause of LBP occurrence in rehabilitation is significant. A previous study demonstrated that hard physical work, frequent trunk rotation or flexion motion, and standing up motion are associated with LBP occurrence (Xu et al., 1997). Medical workers, such as nurses, care workers, and therapists, who work at hospitals frequently perform these motions daily. LBP occurs at a high occurrence rate in medical workers. In Japan, the occurrence rate of LBP within the past month is about 50% in nurses who work at hospitals (Ando et al., 2000).
An electromyographic study demonstrated that the activities of the lumbar erector spinae muscle, gluteus maximus muscle, and hamstrings increase during trunk rotation motion in LBP patients (Pirouzi et al., 2006). Moreover, the activities of the erector spinae and rectus abdominal muscles increase during walking in LBP patients (van der Hulst et al., 2010). However, the relation of these electromyographic data with muscle stiffness is unknown. Overuse of the lumbar erector spinae muscle caused by increased activity may lead to circulatory deficiency within the muscle, resulting in increased muscle stiffness and LBP occurrence. On the other hand, LBP may contribute to increased muscle stiffness (i.e., muscle spasm) of the lumbar back muscles, such as the lumbar erector spinae and lumbar multifidus muscles in LBP patients.
Muscle stiffness of the lumbar back muscles in LBP patients is not clearly elucidated because the stiffness of the individual muscle distinguishing subcutaneous fat and fibrous tissue has been difficult to assess quantitatively. However, the assessment has recently become possible by shear elastic modulus measured using ultrasonic shear wave elastography (SWE). Ultrasonic SWE is a non-invasive and safe ultrasound imaging device. The shear elastic modulus, as an index of muscle stiffness, is evaluated by measuring the shear wave propagation speed in the tissues that is generated by an ultrasonic SWE. Previous studies demonstrated that shear elastic modulus measured by SWE is associated with muscle elongation (Koo et al., 2013, Maïsetti et al., 2012) or muscle strength (Ateş et al., 2015).
Previous studies evaluated muscle stiffness of the upper extremity muscles (Leong et al., 2013, Rosskopf et al., 2016), such as the trapezius and supraspinatus muscles; the lower extremity muscles, such as the rectus femoris, gastrocnemius, and soleus muscles (Akagi et al., 2015); the iliotibial band (Tateuchi et al., 2015, Tateuchi et al., 2016); and the abdominal muscles (Hirayama et al., 2015, MacDonald et al., 2016), such as the rectus abdominis, external oblique, and internal oblique muscles. However, no study has evaluated muscle stiffness individually and quantitatively in LBP patients. Furthermore, previous studies demonstrated the association of LBP with decreased muscle mass of the lumbar back muscles, and with changes in sagittal spinal alignment. Decreased muscle mass of the lumbar multifidus muscle (Barker et al., 2004, Cooper et al., 1992, Hides et al., 1996, Hides et al., 2008, Hodges et al., 2006, Keller et al., 2004) or changes in spinal alignment, such as decreased lumbar lordosis in the standing position (Tsuji et al., 2001), cause stress on intervertebral disks or intervertebral joints, which may contribute to LBP occurrence. A decreased muscle mass in the lumbar erector spinae and quadratus lumborum muscles is also associated with LBP occurrence (Kamaz et al., 2007, Lee et al., 2011). Both muscle stiffness of the lumbar back muscles, and muscle mass of the lumbar back muscles and sagittal spinal alignment, are important factors that could be associated with LBP occurrence.
Therefore, this study aimed to examine the association of LBP with muscle stiffness assessed using ultrasonic SWE and muscle mass of the lumbar back muscles, and sagittal spinal alignment in young and middle-aged medical workers.
Section snippets
Participants
Thirty-two young and middle-aged medical workers in Kyoto Hakuaikai Hospital, Japan were included in the study. The subjects were classified into control (CTR) (n = 23; mean age 34.7 ± 10.2) and LBP groups (n = 9; mean age 44.7 ± 13.0) according to the presence of LBP. The subjects in the CTR group had no LBP at the time of evaluation and no history of LBP lasting 3 or more months. The LBP group consisted of subjects with bilateral or central LBP (except for unilateral LBP) with a severity rating of ≥ 3
Results
Table 1 presents characteristics and LBP status in the CTR and LBP groups. Muscle stiffness and muscle mass of the lumbar back muscle, and spinal alignment are shown in Table 2.
In the reliability analysis of the shear elastic modulus measurement, the ICC values of 1.1 for the erector spinae muscle and lumbar multifidus muscle were 0.784 and 0.913, and the ICC values of 1.2 were 0.879 and 0.954, respectively.
Multiple logistic regression analysis showed that the shear elastic modulus of the
Discussion
Practicing rehabilitation based on the cause of LBP occurrence is important because the cause is attributed to different factors. To the best of our knowledge, this study is the first to examine the association of LBP with muscle stiffness of the lumbar back muscles assessed using ultrasonic SWE in young and middle-aged medical workers. LBP was found to be associated with muscle stiffness of the lumbar multifidus muscle rather than muscle stiffness of the lumbar erector spinae muscle, muscle
Conclusions
The results of the present study suggest that LBP is associated with muscle stiffness of the lumbar multifidus muscle rather than muscle stiffness of the lumbar erector spinae muscle, muscle mass of the lumbar back muscles, or sagittal spinal alignment in young and middle-aged medical workers.
Conflicts of interest statement
No funding sources and potential conflicts of interest were disclosed for the present study.
Acknowledgments
The authors thank all of the individuals who participated in the present study.
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2023, Applied ErgonomicsCitation Excerpt :Diseases of the musculoskeletal system are a major reason for absenteeism of professional drivers (Taylor and Dorn 2006). Typically, discomfort and pain development are affiliated with increased muscle stiffness: For medical workers it has been shown that muscle stiffness of the lumbar multifidus was significantly higher in participants with LBP compared to healthy participants (Masaki et al., 2017). Furthermore, a study by Kett and Sichting (2020) showed a significant increase in stiffness of the lumbar and thoracic spine muscle of office workers after a sitting period of 4.5 h.