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• W2038279797 abstract "Abnormalities of muscle tone are an integral component of many chronic motor disorders affecting the central nervous system (CNS) in children and adults. Excessive, disabling muscle tone is called ‘spasticity'. Spasticity can interfere with movement and can lead to stiff, painful joints [1]. Over half a million people in the United States and 12 million worldwide are affected by spasticity. Spasticity results from dysgenesis or injury to sensorimotor pathways in the cortex, basal ganglia, thalamus, cerebellum, brainstem, central white matter, or spinal cord. Injury occurring in children is known as cerebral palsy (CP) [2]. In adults, CNS injury or disease associated with spasticity includes stroke, spinal cord injury, multiple sclerosis and traumatic brain injury.Although the presence or absence of spasticity can be identified using current clinical scales, the accuracy of determination of spasticity severity and the relationship between severity level and deficits of voluntary movements remain elusive (see [3,4]). These questions are of interest to both researchers and clinicians, because the precise quantification of spasticity is important to establish medical and physical therapeutic effectiveness.We designed a new measure of spasticity, called the Montreal Stretch Reflex Threshold (MSRT) measure, based on a) Lance's definition [5] of spasticity as a motor disorder characterized by a velocity-dependent increase in tonic stretch reflexes with exaggerated tendon jerks, resulting from hyperexcitability of the stretch reflex arc and b) the threshold control theory of motor control [6]. This concept of measurement based on the velocity-dependent stretch reflex threshold is a departure from the more common approach that characterizes the resistance to stretch of the passive muscle (e.g., [7]) and is likely to be more related to motor control deficits than resistance measures. If so, this may lead to a better ability to diagnose the motor impairment in spasticity and may lead to improved patient care. Thus, instead of determining the level of the resistance to stretch of the muscle as is usually done to assess spasticity, the main measure in the new device is the threshold joint angle at which the tonic stretch reflex (TSR) starts to produce resistance, which is clinically identified as spasticity.The measure is based on the motor control theory that shifts in the spatial thresholds of reflexes, including the TSR, underlie muscle force regulation, movement production and muscle relaxation. To meet these requirements in healthy subjects, the CNS regulates the TSR threshold position throughout and beyond the biomechanical range of the joint [6]. In particular, for the muscle to be in a fully relaxed state, the TSR threshold should lie beyond the biomechanical range of the joint. In this case, the muscle cannot be activated by passive movements of the joint within the entire biomechanical joint range. In contrast, to generate forces at a joint angle at which the muscle is maximally shortened, the TSR threshold has to be shifted in the opposite direction to bring it beyond the other end of the biomechanical range. The production of voluntary movement, for example, bending the ankle, occurs due to a shift of the TSR threshold to a value within the biomechanical joint range, which results in the generation of agonist muscle force at the initial joint angle (for details see [6]). The theory thus implies that in the healthy nervous system, the range of TSR threshold regulation exceeds the biomechanical joint range and that a decrease in the range of this regulation leads to the appearance of neurological motor deficits such as spasticity. Thus, the TSR describes where in joint space, spasticity begins to develop. Since this is a threshold position, the measure of torque (a suprathreshold concept) is not required.The system consists of a 2-channel EMG recording module and a high precision electro-goniometer which provide input to a control panel connected through a USB to a computer. EMG signals are recorded from the muscle being assessed (agonist) and its antagonist. The clinician sets the baseline EMG and EMG gain levels on the control panel and then stretches the agonist through its full range of motion. The algorithm guides the operator through the evaluation by signaling how fast to stretch the muscle and displays EMG signals, joint displacement and velocity. The program ensures that the evaluator maintains the same initial joint angle and that EMG is minimal before signaling the start of each stretch. Twenty stretches are performed at different speeds (2 to 400 deg/s). The software computes the SR threshold at each stretch velocity, called ‘dynamic' SR thresholds which are used to compute the TSR threshold (when velocity = 0) in real time. Data are stored on the computer for later analysis if required. The evaluation takes 10–15 min. to complete.An example of the raw data from a single stretch is shown in Fig. 2.TSR thresholds were estimated in 20 subjects (mean age 62.9 ± 13.3, range 37–82 yrs, 16 men) with spasticity in the elbow muscles due to chronic stroke. Tests were done by 3 evaluators to determine the intra-rater (one week apart) and inter-rater reliability of the measure. TSR threshold values were compared to measures of resistance to stretch of the same muscles using the standard clinical measure of resistance (modified Ashworth Scale [8]). Reliability was moderately good for subjects with moderate to high spasticity (intra-rater: 0.46 to 0.68 and inter-rater: 0.53 to 0.68), and less for those with mild spasticity. The TSR threshold measure of spasticity did not correlate with resistance to stretch (MAS) [9]. In another experiment, TSR threshold testing was found to discriminate between different types of increased muscle tone-spasticity and rigidity [10]. Ten subjects with post-stroke spasticity (mean age 65.3 ±12.2 yrs, 6 men) and 11 subjects with parkinsonism (67.3 ±7.9 yrs, 9 men) were tested. Compared to healthy subjects, spasticity and rigidity were associated with a decrease in the range of central regulation of TSR thresholds. SR thresholds were hypersensitive in spastic muscles and either hypo- or inversely sensitive to stretch velocity in rigid muscles.The MSRT is a portable spasticity measurement device that provides quantitative objective measurement of spasticity in a muscle. Unlike other measures of spasticity that quantify the resistance to stretch of a spastic muscle, the MRST identifies the threshold of activation of the tonic stretch reflex (TSR) in that muscle. The TSR threshold is measured as the joint angle at which muscle activity appears during stretching.Research has shown that the TSR threshold instead of muscle resistance is a more precise descriptor of spasticity. The MSRT takes advantage of the physiological principal of velocity-dependence of the SR (i.e., the response depends on how fast the muscle is being stretched) to estimate the tonic SR threshold (the threshold of the SR at rest). The tonic SR threshold is estimated based on the identification of dynamic muscle responses, using EMG recordings, while the clinician stretches the joint at different velocities.An objective tool to measure spasticity may improve standards of practice and communication between clinicians and researchers. The MSRT is portable, easy to use and has good reliability and discriminative ability. The advantage of portability is that it can be applied in the clinic or at the bedside. MRST permits clinicians to interpret TSR threshold values together with the relationship between stretch velocity and threshold angle, which more closely satisfies the classic definition of spasticity according to Lance [5] than scales measuring resistance to stretch." @default.
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• W2038279797 date "2013-07-03" @default.
• W2038279797 modified "2023-10-01" @default.
• W2038279797 title "A New Standard in Objective Measurement of Spasticity" @default.
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