1. Clinical data
Healthy volunteers
Inclusion Criteria:
①patients in good physical health,
②patients aged 20 to 55 years, including 20 and 55 years, male or female,
③patients who agree to participate in the study and sign the informed consent.
Exclusion criteria:
①patients who performed lumbar and abdominal muscles exercises in the past,
②patients unable to tolerate magnetic resonance imaging or claustrophobia,
③patients who are deemed unsuitable for the clinical trial.
Removing criteria:
①patients who decline participation of various reasons,
②patients unable to comprehend questions asked by the researchers,
③patients intolerant to necessary examinations.
Patients with LDH
Inclusion Criteria:
①patients who meet the diagnostic criteria for LDH[10];
②patients aged 20 to 55 years, including 20 and 55 years, male or female,
③Patients with a history of LDH for 6 months and/or above
④patients who have signed the informed consent.
Exclusion criteria:
①patients with LDH causing radiculopathy (radicular pain and paresthesia) or cauda equina syndrome,
②patients with other diseases such as spinal stenosis, ankylosing spondylitis that cause low back pain,
③patients with a previous history of spinal surgery, traumatic injury to the spine,
④patients with bone tuberculosis, osteoporosis and bone tumors,
⑤patients with other severe cardiovascular and cerebrovascular diseases, digestive and hematopoietic system diseases, patients with diabetes mellitus Autoimmune diseases or other metabolic diseases, patients with mental diseases,
⑥patients who performed lumbar and abdominal muscles exercises in the past,
⑦patient had a previous history of wearing lumbar supports for at least 2 weeks,
⑧patients unable to tolerate magnetic resonance imaging or claustrophobia,
⑨patients inappropriate for participation in the present study for any other reason.
Removing criteria:
①patients who decline participation of various reasons,
②patients unable to comprehend questions asked by the researchers,
③patients intolerant to necessary examinations.
2.Methods
The epidemiological studies were conducted using a case-control design. Fifthy-five healthy individuals were selected as controls. Magnetic resonance imaging-guided core muscles percent fat in patients with LDH and healthy volunteers including erector spinae, rectus abdominis, (transversus abdominal, internal abdominal oblique, and external abdominal oblique muscle), lumbar multifidus, and psoas major muscles was used as as the outcome measure, logistic regression as the analytical method to investigate the relationship between degeneration of core muscles and LDH.
The method of core muscles percent fat detection
MRHS was used to measure different muscle percent fat of core muscles. MRHS also called Dixon imaging mainly used the different resonant frequency between the hydrogen nuclei in water and in fat to perform data acquisition at different echo times (TE). The Dixon sequence basically acquires two images, one image with water and fat signals in-phase and the other with water and fat signals out-of-phase: the sum and subtraction of the two images allows the production of a water-only image and a fat-only image. Scanning equipment: 3.0T superconducting Siemens Skyra Scanner.
Scanning parameters: TR5.36ms, TE1.24ms, Flip Angle 9°, number of layers was 44-60, thickness of layer was 5.0 mm, layer interval 1.0mm, FOV50cm×50cm, the scanning time was 12s×5.
Measurements: Image acquisition (see Figure 2), percent fat measurement and data recording of each muscle of core muscles at the level of the L4-L5 intervertebral disc space were performed jointly by a senior orthopaedic surgeon and two high-grade imaging physicians.
Sample size calculation
A case-control research design was adopted for the study. The sample size was estimated based on multiple logistic regression analysis, requiring a sample size of more than 20 times the number of independent variables. Given the difficulty of matching patients between groups based on their baseline data and the experimental feasibility, fifty-five healthy volunteers and fifty-five patients with LDH were recruited in this study.
Ethics statement
This study was reviewed and approved by the Independent Ethics Committee of Shuguang Hospital Affiliated to Shanghai University of Traditional Chinese Medicine on April 29, 2015 (No. 2015-384-12-01) and conducted in compliance with current Chinese law and the principles of Declaration of Helsinki to protect the rights and interests of patients.
3.Statistical analysis
All statistical analyses were completed by the statistical software SPSS17.0. Variables followed a normal distribution were given as mean ± standard deviation and then the independent t-test was performed. Variables which didn’t followed a normal distribution were analyzed either after log transformation or using the Wilcoxon rank sum test. Continuous variables found to be statistically significant using the independent two-sample t test and grades variables using the Wilcoxon rank sum test then were analyzed by univariate logistic regression analysis. Variables found to be statistically significant in univariate analyses were entered into multivariate logistic regression analysis (the stepwise regression analysis). Results were reported as β-Coefficients, p-values, Exp and 95% confidence intervals. Core muscles percent fat values were divided into 4 levels by quartiles to include into the multivariable logistic regression model.