Relationship between spasticity and muscle’s structure and mechanical properties
(2022) ISPRM 2022 — Location: Lisbon Congress Center (3.July.2022)
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- Abstract
- Introduction: Approximately half of the people with stroke present with impaired gait and/or upper-limb function due to muscle hyper-resistance (HR). The neural components of HR can be velocity dependent (spasticity) or not (spastic dystonia, co-contractions). Concurrently, a modification of the muscle’s structure occurs due to the impaired central nervous system command and results in modifications of muscle’s mechanical properties, with shortening and loss of extensibility of muscles, a reduction of cross-sectional area and neurogenic atrophy, a decrease in fiber size, an increase of collagen proportion and of intramuscular lipid accumulation. This impacts muscle’s stiffness (viscosity and elasticity), which constitutes the non-neural component of HR (sometimes referred to as spastic myopathy). Some of the treatments used for HR, such as botulinum toxin (BTX) injections, which are considered standard of care, may also impact muscle structure and its mechanical properties. The neural and non-neural components of HR and muscle structure can be assessed by different techniques. Stiffness: The assessment of HR is mostly based on the use of two clinical scales, the Modified Ashworth Scale and the Modified Tardieu Scale, that still constitute the gold-standard of spasticity evaluation. They allow a non-linear grading of the resistance of muscles to passive stretch at a supposedly controlled speed. Although these scales remain useful on a clinical setting since they require no material and very little time, their inability to distinguish between the different components of HR is now widely accepted. Some objective measurement tools have emerged in the past decade, including motor-driven devices imposing isokinetic extensions at controlled speeds, electromyography-equipped electronical goniometers and electromechanical oscillatory devices, amongst others, which measure resistance to movement and help differentiate between the different components of HR in an objective way. Recently developed echography sequences, such as shear wave elastography (SWE), are increasingly used to assess muscle stiffness. Structure: Magnetic resonance imagery is considered the reference tool for non-invasive muscle structure evaluation. Acquisitions using the Dixon technique allow the quantification of the fat fraction present in every image voxel and thus help quantify fat and collagen muscle content. Diffusion tensor-imaging (DTI) allows the study of the diffusion of water molecules in tissues along different directions. In muscles, DTI has proven capable to accurately determine fascicle length and orientation. Relationship between HR treatment, muscle structure and stiffness: Surgical and chemo-denervation have been shown to have consequences on muscle structure and stiffness, but these consequences remain poorly understood. Some authors have shown that measures of SWE are responsive to BTX injection, and that elastographic and clinical measurements are correlated. Conclusion: This presentation will discuss the relation between HR, muscle structure and mechanical properties. It will also address how BTX injections impact these by reviewing the most recent evaluation tools and techniques.
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Selves, C., & et al. (2022). Relationship between spasticity and muscle’s structure and mechanical properties. ISPRM 2022, Lisbon Congress Center. https://hdl.handle.net/2078.5/27937