The Ashworth Scale is an instrument that measures the degree of spasticity or increased muscle tone , a problem that causes the patient stiffness and a loss of balance between the contraction and relaxation of the muscles. It is a scale that must be applied and completed by the professional, with the help of the patient.
In the article we explain what the Ashworth scale and its modified version consists of, what the items are that make it up, how it is applied and what its psychometric properties are.
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What is the Ashworth scale?
The Ashworth Scale, also called the Ashworth Spasticity Scale, is a diagnostic instrument used to measure muscle tone and spasticity, i.e. the ability of muscles to hold themselves slightly contracted.
This scale was originally created by Ashworth in 1964 and was later modified by Bahannon and Smith in 1989 into what is now known as the modified Ashworth scale. This new version better measures muscle hypertonia.
This instrument consists of a clinical scale for subjective evaluation that allows direct assessment of muscle spasticity from no increase in muscle tone to extreme rigidity when flexing or extending muscles.
The Ashworth scale was validated with neurological patients with different degrees of spasticity and has shown great interobserver reliability, both in the evaluation of spasticity of elbow flexors and in the measurement of spasticity of plantar flexors.
The modified scale adds elements that include the angle at which the resistance appears, controlling the speed of passive movement with a count of 1 second. This improved version is easy to use and works for all joints (although it performs better with the upper extremities). However, it still has points to improve, in the degree of discrimination (between +1 and -1 degrees) or sensitivity.
Items and application of the scale
The modified Ashworth scale contains five main items, in a graduation from 0 to 4, including an additional item in the 1 scale.
Being a subjective rating scale, the score depends on the personal appreciation of the health professional applying it. It is important to know that this scale is heteroadministered, since neither the patient nor unqualified personnel are suitable for its application.
After observing the patient, the practitioner should assign values from 0 to 4, with the following meaning
0: Normal muscle tone , no increase in muscle tone at all
1: Mild hypertonia : consists of an increase in muscle tone, either through flexion or extension. It can be observed through palpation or relaxation and involves some resistance at the end of the arc of muscle movement.
1+: Slight increase in the resistance of the muscular response to movement in flexion or extension, followed by minimal resistance throughout the remainder of the arc of travel (less than half). This item complements the previous one,
2: Moderate hypertonia : this item implies a notable increase in the resistance of the muscle during most of the arc of joint movement, despite the fact that the joint moves easily and does not limit its movement excessively.
3: Intense hypertonia : consists of a marked increase in muscular resistance and implies that passive movement is executed with difficulty.
4: Extreme hypertonia : this last item implies that the affected parts are completely rigid, in flexion or extension, even when moving passively.
The psychometric properties of an instrument or rating scale include properties such as validity or reliability, aspects that take into account how effective and reliable an instrument is in assessing what it claims to measure, or the degree to which each of its component elements contributes to the stability of the measurement of each characteristic.
The modified Ashworth Scale has several psychometric studies that have assessed its psychometric properties in order to test its effectiveness and reliability in measuring and assessing muscle spasticity and hypertonia.
The main conclusions reached are as follows:
L on the Ashworth scale is reliable, useful and valid , as it responds correctly to the passive movement made by the healthcare professional in a particular joint.
The modified scale has a greater variety of items than its predecessor, because the evaluation is made by joints and in each of the subject’s hemicorcles. There are also certain differences in the evaluation process.
The diagnostic instrument is an evaluative tool that provides an appropriate assessment by requiring quantitative clinical measures of the spasticity involvement of each subject.
It is an appropriate tool for assessing spasticity over time and thus for monitoring the patient’s improvement.
The reliability coefficient of the test tends to its maximum expression , so the scale seems to be an instrument free of random errors, as it is observed that the scores of successive diagnoses have been stable in the different evaluations.
The modified Ashworth scale has proved to be a reliable instrument for both upper and lower limb spasticity assessment.
One of the negative aspects of the scale is that it seems to have low levels of sensitivity when there is little variability in the degree of spasticity of the subjects.
As a subjective instrument, there are limitations related to the profile of each professional evaluator.
Other tests that evaluate spasticity
Beyond the Ashworth scale, there are a number of other tests capable of measuring spasticity. Some of the better-known ones include:
1. Count the clone pulses
In this test, the examining practitioner looks for the presence and amount of muscle contractions and relaxations (pulses) that make movements, above and below the ankle, wrist, and other joints.
The scale is graduated from 0 to 3: 0 being the absence of pulses; 1 being non-sustained or few pulses; 2 being sustained or continuous pulses; and 3 being spontaneous or caused by a light or sustained touch.
2. Tardieu Scale
The Tardieu scale is an instrument in which the evaluating professional moves the patient’s muscles at different speeds , quickly and slowly, to observe if the resistance changes according to the speed of the movement.
The scale is graduated from 0 to 4 with 0 being no resistance through the course of stretching; 1 being poor resistance at a specific angle through the course of stretching, with no clear muscle attachment; 2 being clear attachment at a specific angle, interrupting the stretch, followed by relaxation; 3 being clone at a specific angle lasting less than 10 seconds while the assessor maintains pressure; and 4 being the same as the item, except for the duration, which must be greater than 10 seconds.
3. Penn Scale of Spasm Frequency
This scale aims to report how often muscle spasms occur . It is graduated from 0 to 4 as follows: 0, no spasms; 1, spasms induced only by stimuli; 2, spasms occurring less than once every hour; 3, spasms occurring more than once every hour; and 4, spasms occurring more than 10 times every hour.
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Calderón-Sepulveda, R. F. (2002). Scales for measuring motor function and spasticity in cerebral palsy. Rev Mex Neuroci, 3(5), 285-89.
Vattanasilp W, Ada L. Comparison of the Ashworth scale and clinical laboratory measures to assess spasticity. Aust J. Physiother 1999; 45: 135-139.