Modified Ashworth Scale

Modified Ashworth Scale

The modified scale is considered a resistance to passive movement scale rather than a direct spasticity scale as similarly, the original Ashworth scale looks at the resistance to passive movement of extremities, not just stretch-reflex hyperexcitability:

■ No increase in muscle tone. (0)

■ Slight increase in muscle tone, manifested by a catch and release or by minimal resistance at the end of the range of motion when the affected part(s) is moved in flexion or extension. (1)

■ Slight increase in muscle tone, manifested by a catch, followed by minimal resistance throughout the reminder (less than half) of the ROM (range of movement). (+1)

■ More marked increase in muscle tone through most of the ROM, but affected part(s) easily moved. (2)

■ Considerable increase in muscle tone passive, movement difficult. (3)

■ Affected part(s) rigid in flexion or extension. (4)

The populations reviewed with the modified Ashworth scale are of adults and children with Central Nervous System (CNS) lesions that have lead to:

■ Multiple Sclerosis;

■ Cerebral Palsy;

■ Spinal Cord Injury;

■ Pediatric Hypertonia;

■ Stroke;

■ Traumatic Brain Injury.

Original Ashworth Scale

■ No increase in tone. (0)

■ Slight increase in tone giving a catch when the limb was moved in flexion or extension. (1)

■ More marked increase in tone but limb easily flexed. (2)

■ Considerable increase in tone - passive movement difficult. (3)

■ Limb rigid in flexion or extension. (4)

Scale administration

Both the original and modified versions of the scale don’t take long to administer and can be performed in less than 5 minutes.

In order to ensure inter-rater reliability, it is recommended that the assessor have knowledge of the musculoskeletal system and the connections with neurological mechanisms and spasticity. This also links into one of the criticisms of the model, the fact that its administration is not completely standardized.

The AS and MAS methods examine muscle tone during flexion and extension. The first instruction is that the patient need to be placed on the therapy mat in supine position.

The flexor muscles of a joint, either from upper or lower body, are placed in a maximally flexed position and moved to a maximally extended position over a 1 second span.

The extensor muscles of a joint are checked in maximal extension and then are moved to a maximally flexed position over a 1 second period.

Each movement is then correlated with the scale items. In some cases, movement may have to be repeated but the same muscles should not be tested for more than three times in a row.

Interpretation

The original Ashworth scale consists of five items, numbered from 0 to 4. The modified version includes a sixth item which comes between 1 and 2 and is noted as +1, thus the modified version also remains within 0 and 4.

Scores closer to 0 indicate no or very little resistance while scores closer to 4 are indicative of muscle/joint rigidity.

Once an item is selected, the result explains its position in the scale and displays a comparison table between the original and modified version.

About the study

The modified Ashworth scale was created and tested by Dr Bohannon to determine the interrater reliability of manual tests of elbow flexor muscle spasticity. The study involved 30 patients with intracranial lesions whose elbow flexor muscle spasticity was tested.

Subsequent validation studies have looked at different disability inducing neurological conditions. The interrater reliability was found to be 42.5-50% while the intrarater reliability performed slightly better in the range of 57.7-85%.

Original source

Bohannon RW, Smith MB. Interrater reliability of a modified Ashworth scale of muscle spasticity. Phys Ther. 1987; 67(2):206-7.

Other reference

Ansari NN, Naghdi S, Arab TK, Jalaie S. The interrater and intrarater reliability of the Modified Ashworth Scale in the assessment of muscle spasticity: limb and muscle group effect. NeuroRehabilitation. 2008; 23(3):231-7.