Testing Spasticity: The Modified Ashworth Scale

There are folks who think that spasticity is a good thing, that there is logic behind it, that there is a “because” to spasticity. They say that spasticity exists because soft tissue needs protection. That is, spasticity keeps the joints in a fixed position, for protection of soft tissue, especially muscle.

Of course, if spasticity is protective, it is a rather blunt instrument. Spasticity is usually not just the agonists or just the antagonists firing. It is a co-contraction of the flexors, extensors and all combined agonists. In the arm, spasticity is often represented with all joints flexed and the limb held close to the body. Shoulder internal rotation, elbow flexion and wrist and fingers collection is a representation of the relative strength of the flexors over the extensors.

That is, the elbow is flexed not because the triceps are not spastic. Instead, it is flexed because the elbow flexors are so much stronger than the elbow extensors. In the lower-extremity, spasticity is usually representing the relative strength of the plantar flexors, knee extensors and hip internal rotators.

Therapies are first line of defense against spasticity but therapists rarely measure spasticity. Therapists try to evaluate spasticity by judging changes in movement, improvements in ADLs or “getting a feel” for the amount of resistance. But since there is no measurement there’s no way of telling if an intervention is working.

For Good Measure

One quick and easy way to measure spasticity is the Modified Ashworth Scale (MAS). The MAS measures resistance during passive soft-tissue stretching. These are the general rules:

• The MAS is done in supine (this will garner the most accurate and the lowest score; any tension anywhere in the body will increase spasticity);
• Because spasticity is “velocity dependent” (the faster the limb is moved, the more spasticity is encountered), the MAS is done moving the limb at the “speed of gravity.” This is defined as the same speed a non-spastic limb would naturally drop. In other words, fast;
• The test is done a maximum of three times for each joint. If it is done more than three times the short-term effect of a stretch impacts the score;
• The MAS is done prior to goniometric testing. Goniometric testing provides a stretch and the short-term effect of a stretch impacts the score.

Here are the positions usually used for the MAS.

Elbow. Start position: Elbow fully flexed, forearm neutral. Movement: Extend elbow from maximum possible flexion to maximum possible extension. (Triceps would be the same position, opposite direction.)

Wrist. Start position: Elbow as straight as possible, forearm pronated. Movement: Extend the patient’s wrist from maximum possible flexion to maximum possible extension.

Fingers. Start position: Elbow as straight as possible, forearm neutral. All fingers are done at once. Movement: Extend the patient’s fingers from maximum possible flexion to maximum possible extension.

Thumb. Start position: Elbow as straight as possible, forearm neutral, wrist in neutral. Movement: Extend the thumb from maximum possible flexion (thumb against index finger) to maximum possible extension (in anatomical position, “abducted”).

Hamstrings. Start position: Prone so that ankle falls beyond end of the plinth, hip in neutral rotation. Movement: Extend the patient’s knee from maximum possible flexion to maximum possible extension.

Quadriceps. Start position: Prone so that ankle falls beyond end of the plinth, hip in neutral rotation. Movement: Flex the patient’s knee from maximum possible extension to maximum possible flexion.

Gastrocnemius. Start position: Supine, ankle plantarflexed, hip in neutral rotation and flexion. Movement:Dorsiflex the patient’s ankle from maximum possible plantarflexion to maximum possible dorsiflexion not more than three consecutive times and rate the muscle tone.

Soleus. Start position: Supine, ankle plantarflexed, hip in neutral rotation and flexion and with the knee flexed to ~15°. Movement: Dorsiflex the patient’s ankle from maximum possible plantarflexion to maximum possible dorsiflexion.

The problem with the MAS is both ends of the scale. Technically the MAS is a scale for grading the resistance encountered during PROM. It is not specifically a test of spasticity. A score of “0” does not mean “no tone,” it means normal tone. So there is no score for less than normal tone (flaccid). A score of “4” does not tell you if the rigidity of the joint is due to a high amount of spasticity or contracture.

On the plus side, the Modified Ashworth is a quick an easy measure that can help in taking the guesswork out of efficacy of treatment.

Resource
Bohannon, R. et al. (1987). Interrater reliability of a Modified Ashworth Scale of muscle spasticity. Physical Therapy, 67, 206-207.

Levine, P. (2018). Stronger After Stroke, 3rd ed. (pp. 193-198) New York, NY: Demos Medical Publishing.

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