Modified Ashworth Scale for Spasticity Assessment
The Modified Ashworth Scale (MAS) is a 6-point ordinal scale (0,1+, 2,3,4) that quantifies spasticity by measuring resistance to passive movement, with scores ranging from 0 (no increase in tone) to 4 (affected part rigid in flexion or extension), and takes approximately 10 minutes to administer across multiple joints 1.
Scoring System
The MAS grades spasticity based on the clinician's perception of resistance during passive joint rotation:
- 0: No increase in muscle tone
- 1: Slight increase in muscle tone, manifested by a catch and release or minimal resistance at the end of range of motion
- 1+: Slight increase in muscle tone, manifested by a catch, followed by minimal resistance throughout the remainder (less than half) of the range of motion
- 2: More marked increase in muscle tone through most of the range of motion, but affected part(s) easily moved
- 3: Considerable increase in muscle tone, passive movement difficult
- 4: Affected part(s) rigid in flexion or extension
Clinical Application
The MAS is recommended by the American Heart Association/American Stroke Association guidelines as the standard clinical tool for quantifying spasticity in stroke rehabilitation settings 1. The scale can be applied to any joint but is most commonly used to assess upper and lower extremity muscle groups. Higher scores indicate greater severity of spasticity and correlate with increased resistance to passive movement 1.
Administration Considerations
The assessment involves passive movement of the limb through its full range of motion at a standardized velocity. The clinician rates the resistance felt during this movement. When assessing multiple joints, the complete evaluation takes approximately 10 minutes 1.
Reliability and Validity Concerns
While the MAS is the most widely used clinical scale for spasticity assessment 2, research reveals important limitations:
- Interrater reliability is only moderate (kappa = 0.514), with better agreement for distal upper extremity muscles (particularly wrist flexors) compared to proximal muscles 3
- Intrarater reliability is similarly moderate (kappa = 0.590) 3
- The scale demonstrates minimally adequate reliability for plantarflexor assessment in traumatic brain injury patients 4
- The MAS may measure muscle hypertonia rather than pure spasticity, as the relationship between MAS scores and alpha motor neuron excitability is not linear 5
Clinical Pitfalls
The qualitative nature and low resolution of the scale can result in varied grouping of patients even within a single score category 6. The 1+ score is particularly problematic, showing varied electromyographic and goniometric patterns across patients with the same clinical grade 6. Despite these limitations, the MAS remains the recommended standard due to its widespread use, ease of administration, and established role in guiding treatment decisions for interventions like botulinum toxin injection 7, 1.