Assesschild

Standardized Assessments for the Management of Children with Motor Disorders

modified ashworth scale (mas)

Assessment Authors: Bohannon & Smith (1987)

Description of Assessment

Purpose: Evaluation of Hypertonia. Most studies of clinical spasticity measurement and treatment of spastic paresis have consistently utilized the Modified Ashworth Scale, a tone or stiffness measuring scale, that has become a de facto criterion standard. However, the scale simply measures the resistance to passive movements of a joint which is not an exclusive measure of spasticity.

Therefore, to be more precise, the purpose of the MAS is the evaluation of hypertonia.

Hypertonia is defined as abnormally increased resistance to externally imposed movement about a joint. It may be caused by (1) spasticity, (2) dystonia, (3) rigidity (immovable joint), or (4) a combination of features.

Assessment Details

In an effort to improve the reliability of the MAS, Bohannon and Smith (1987) proposed to:

Test the patient in the supine position.
Extend the joint from a position of maximal possible flexion to maximal possible extension.
Standardize hand positioning and the resting limb position before stretch. However, Bohannon and Smith provided instructions for the elbow only. For the purposes of this educational program, specific step by step procedure guidelines were developed by the investigators for 2 upper limb and 2 lower limb joints.
Standardize the timing of the extension of the limb: Use a duration of about one second (by counting "one thousand one").
Keep repeated movement cycles at a minimum. Repeat the measurement 5 to 8 times and choose the most reliable / consistent measurement.

To further improve the reliability of the MAS, investigators for this educational program propose that the available range of motion be subdivided into quarters. Increased muscle tone, resistance, catch & release or clonus will be rated according to the location within these quarters:

Refers to a catch and release / clonus OR minimal resistance in the 4th quarter of the available range of motion.

Refers to a catch and release / clonus followed by minimal resistance in the 3rd quarter of the available range of motion.

2 or 3

Refers to an increase in muscle tone that begins in the 1st or 2nd quarter of the available range of motion.

Key components of reliably measuring tone using the MAS include:

Understanding of MAS definitions and accurately calculating the quarters of available range.
Keeping the patient's body and limb position the same & stabilization of the proximal limb segment.
Using standardized hand placement for the clinicians.
Using a consistent speed of movement of one second for the full available range.
Ability of clinicians to recognize the different manifestations of muscle resistance.
Ability of clinicians to identify maximum flexion, maximum extension, and pinpoint the location where resistance begins.
Accurate recording of all measurements and calculations.
The need to practice of standardized process to gain proficiency and accuracy - even for skilled clinicians.

Rating System

Simple numerical rating of the resistance to passive movement about a joint measured on a scale of 0 (no resistance) to 4 (immovable joint).

0	No increase in muscle tone. Normal muscle tone.
1	Slight increased in tone, manifested by a catch and release or by minimal resistance at the end of the range of motion when the affected part is moved in flexion or extension. [4th QUARTER]
1+	Slight increased in tone, manifested by a catch, followed by minimal resistance throughout the remainder (less than half) of the range of motion. [3rd QUARTER]
2	More marked increase in muscle tone through most of the range of motion, but affected parts are easily moved. [1st or 2nd QUARTER]
3	Considerable increase in muscle tone; passive movements difficult. [1st or 2nd QUARTER]
4	Affected part rigid in flexion or extension.