Comparison of the Stiffness of the Lumbar Back Muscles Between Low Back Pain and Healthy Controls Using Magnetic Resonance Elastography and Shear Wave Elastography

"Chronic low back pain (CLBP) is commonly associated with increased trunk stiffness detected by quick release methods and motion track systems as well as increased back muscles stiffness identified by manual palpatory procedures or strain elastography. However, these techniques are qualitative and operator dependent, hence they remain poorly reliable.

Over the last decade, imaging techniques have become very helpful to characterize the biomechanical properties of tissues in vivo. Today, supersonic shear wave elastography (SWE) allows real time mapping of the elastic shear modulus. Also, magnetic resonance allows mapping and quantifying stiffness within a large volume of tissue. Elastography is efficient in the characterization of passive and active muscle forces, in highlighting the influence of muscle stiffness on joint stiffness and in showing stiffness changes related to muscle diseases Imaging plays a key role in the management of CLBP; It allows to reach specific radiological diagnosis such as tumor, inflammatory, or arthritis. However, in many cases, MRI did not find a specific cause to low back pain and the low back pain is reported as "non-specific". Myofascial disorders are also responsible for non-specific CLBP.

The main objective of this study is to compare the shear modulus of the main lumbar back muscles (erector spinae and multifidus) between patients with low back pain and healthy controls.

Second objectives are to assess: the relationship between the stiffness of the back muscles and clinical stiffness, the influence of age and sex on the elasticity of the back muscles, the relationship between the surface of the paravertebral muscles and the elasticity; the relationship between the elasticity of the hypaxial muscles (in front of the spine) and the epaxial muscles (behind the spine =back muscles), the relationship between fatty infiltration and elasticity of the back muscles, the relationship between inflammation / edema of back muscles and stiffness of the back muscles, the influence of the muscular stretching on the elasticity of the paravertebral muscles, the difference of elasticity in the direction of the muscle fibers (oblique coronal) and perpendicular (axial), the stiffness difference the between the right and left muscles, the role of different postures on muscle elasticity, the relationship between the elasticity of the back muscles and the intensity and type of pain, the relationship between the elasticity of the paravertebral muscles and disco-vertebral and / or posterior apophyseal pathology.

The inclusion of 26 patients and 26 controls will demonstrate a difference in mean elasticity modulus of 1.1 standard deviation (between patients and controls), with 90% and an alpha risk of 5%.