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.

TL;DR: The results of this study suggest that LBP is associated with muscle stiffness of the lumbar multifidus muscle in young and middle‐aged medical workers.

About: This article is published in Clinical Biomechanics.The article was published on 2017-11-01 and is currently open access. It has received 61 citations till now. The article focuses on the topics: Muscle stiffness & Multifidus muscle.

Summary

1. Introduction

• The occurrence rate of low back pain (LBP) within the lifetime of adults is about 80% (Waddell, 1987).
• LBP occurs at a high occurrence rate in medical workers.
• The relation of these electromyographic data with muscle stiffness is unknown.
• 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.
• 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).

2.1. Participants

• Thirty-two young and middle-aged medical workers in Kyoto Hakuaikai Hospital, Japan were included in the study.
• The LBP group consisted of subjects with bilateral or central LBP (except for unilateral LBP) with a severity rating of ≥3 on the numerical rating scale (NRS) in both static (i.e., lying, sitting, or 6 standing) and dynamic situations (i.e., moving or walking), lasting 3 months or more at the time of evaluation.
• Medical workers included nurses, care workers, and therapists.
• The protocol was approved by the Ethics Committee of the Kyoto University Graduate School and Faculty of Medicine.

2.2. Low back pain assessment

• The duration and degree of LBP, as well as the disabilities of daily living due to LBP, were assessed in the LBP group using a questionnaire.
• The degree of LBP was examined using the NRS in both static (i.e., lying, sitting, or standing) and dynamic situations (i.e., moving or walking).
• The disabilities of daily living due to LBP were assessed using the Oswestry disability index (ODI) (Fairbank and Pynsent, 2000).
• The item of sex life, which can be removed if not applicable, was not used in this study.
• The sum of each item was expressed as a percentage, and a large percentage indicated the severe disabilities of daily living due to LBP.

2.3. Ultrasound measurement

• Images of the lumbar back muscles were taken using an ultrasound imaging device with SWE (Aixplorer, Supersonic Imagine, Aix-en-Provence, France).the authors.
• Ultrasound images were measured once bilaterally for muscle thickness.
• A previous study showed that the degree of intrarater reliability of the ultrasound technique is high for measuring muscle thickness of the lumbar back muscles (Masaki et al., 2015).
• A linear array probe was set parallel to the muscle fibers to measure the shear elastic modulus accurately (Eby et al., 2013).
• Three ROIs with a diameter of 10 mm were set in the color-coded box, with 1 located at the center of the box and the other 2 beside the initial ROI.

2.4. Measurement of spinal alignment

• The Spinal Mouse (Index Ltd., Tokyo, Japan) was used to measure sagittal spinal alignment in the standing position (thoracic kyphosis, lumbar lordosis, and sacral anterior inclination angle) based on a previous study (Masaki et al., 2015).
• Spinal alignment in the prone position was also measured to identify whether muscle stiffness and muscle mass of the lumbar back muscles were influenced by spinal alignment in the position of ultrasound measurement.
• The Spinal Mouse was guided along the midline of the spine, starting at the C7 spinous process and ending at S3.
• The lumbar lordosis angle was calculated from the sum of the 6 segmental angles from Th12/L1 to L5/S1.
• The sacral anterior inclination angle was calculated from the difference between the sacral angle and the vertical plane.

2.5. Statistical analyses

• Statistical analyses were performed using SPSS version 22.0 (IBM Japan; Tokyo, Japan).
• Intraclass correlation coefficients [ICCs (1.1), ICC (1.2)] were calculated to examine intrarater reliabilities of the shear elastic modulus measurements.
• Furthermore, the associations with LBP were investigated by multiple logistic regression analysis with a forward selection method.
• This analysis was conducted using the shear elastic modulus and muscle thickness of the lumbar back muscles, and sagittal spinal alignment, age, body height, body weight, and sex as independent variables.
• P values of <0.05 were considered significant.

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.
• The shear elastic modulus of the lumbar multifidus muscle in the LBP group was significantly higher than that in the CTR group.
• The height in the LBP group was significantly lower than that in the CTR group (Table 3).
• Multiple logistic regression analysis also showed that the other factors were not significant independent determinants of LBP.

4. Discussion

• Practicing rehabilitation based on the cause of LBP occurrence is important because the cause is attributed to different factors.
• Muscle stiffness of the lumbar multifidus muscle is assumed to increase by muscle contraction.
• Previous study (Chan et al., 2012) demonstrated muscle stiffness of the lumbar back muscles using a strain imaging method of the ultrasound imaging device, which is different from ultrasonic SWE used in the present study.the authors.
• They targeted only the lumbar multifidus muscles in the LBP patients and suggested that no significant difference exists in the muscle stiffness of the lumbar multifidus muscle in the prone position between healthy subjects and LBP patients.
• The results of the present study were consistent with those of the previous studies that demonstrate no association with spinal alignment in the standing position and LBP.

5. 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.
• No funding sources and potential conflicts of interest were disclosed for the present study.

Figures

Fig. 2. Muscle stiffness measurement of the lumbar back muscles in young and middle-aged medical workers.

Table 1 Characteristics and LBP status in the CTR and LBP groups.

Table 2 Muscle stiffness and muscle mass of the lumbar back muscles, and spinal alignment in the CTR and LBP groups.

Table 3 Results of multiple logistic regression analysis with a forward selection method.

Fig. 1. Muscle thickness measurement of the lumbar back muscles in young and middle-aged medical workers.

Frequently asked questions

Q1. What contributions have the authors mentioned in the paper "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" ?

This study aimed to examine the association of LBP with muscle stiffness assessed using ultrasonic shear wave elastography ( SWE ) and muscle mass of the lumbar back muscle, and spinal alignment in young and middle-aged medical workers. The study comprised 23 asymptomatic medical workers [ control ( CTR ) group ] and 9 medical workers with LBP ( LBP group ). The association with LBP was investigated by multiple logistic regression analysis with a forward selection method. The results of this study suggest that LBP is associated with muscle stiffness of the lumbar multifidus muscle in young and middle-aged medical workers. 

Q2. What are the future works mentioned in the paper "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" ?

In this case, the overuse caused by muscle spasm of the lumbar multifidus muscle may lead to circulatory difficulty within the muscle, which contributes to secondary LBP occurrence in the future. Further studies should examine training for improving muscle stiffness of the lumbar multifidus muscle effectively. They targeted only the lumbar multifidus muscles in the LBP patients and suggested that no significant difference exists in the muscle stiffness of the lumbar multifidus muscle in the prone position between healthy subjects and LBP patients. The present study suggests that LBP is associated with muscle stiffness of the lumbar multifidus muscle in young and middle-aged medical workers. 

Q3. What causes muscle spasm in the lumbar multifidus?

which is caused from stress on intervertebral disks or intervertebral joints, may induce muscle spasm of the lumbar multifidus muscle. 

Q4. What is the reason for the association of LBP with muscle stiffness?

Circulatory difficulty within the lumbar multifidus muscle caused by overuse during the motions may contribute to an increase in muscle stiffness and LBP occurrence. 

Q5. How many ROIs were set in the color-coded box?

Three ROIs with a diameter of 10 mm were set in the color-coded box, with 1 located at the center of the box and the other 2 beside the initial ROI. 

Q6. What is the reason for the association of LBP with muscle stiffness of the lumbar?

A possible reason for the association of LBP with muscle stiffness of the lumbar back muscles in the prone position is the frequent trunk flexion or pelvic anterior tilt of the medical workers in the standing position during medical treatment, care, and rehabilitation, as well as frequent extension of their trunk during transferring patients. 

Q7. Who was blinded to information of the groups?

The determination of the ROIs and the computation of muscle thickness and shear elastic modulus were performed by 1 examiner who was blinded to information of the groups. 

Q8. What is the reason for the inconsistency in the measurements of muscle mass?

This inconsistency may be attributed to the flexion of the lumbar spine, which compensatorily becomes excessive during12medical treatment, care, rehabilitation, and transferring patients in medical workers, who have shorter body height (i.e., shorter upper extremities). 

Q9. What is the effect of the shorter body height on the lumbar multifidus muscles?

shorter body height may contribute to increased muscle stiffness of the lumbar multifidus muscles, or the stress on intervertebral disks or intervertebral joints. 

Q10. What is the shear elastic modulus of the lumbar erector spina?

The shear elastic modulus (G) was computed from the shear wave propagation speed (v) and the muscle mass density (ρ) using the following equation: G=ρv2 where ρ is presumed to be 1000 kg/m3 (Aubry et al., 2013). 

Q11. What is the reason for the lack of measurements of muscle mass?

whether an increase in muscle stiffness of the lumbar multifidus muscle is caused by overuse or muscle spasm is unclear because the activities of the lumbar back muscles were not measured using electromyography during ultrasound measurement.