Biomechanical measurement of post-stroke spasticity

Background: spasticity following stroke is common, but clinical measurement is difficult and inaccurate. The most common measure is the modified Ashworth scale (MAS) which grades resistance to passive movement ( RPM), but its validity is unclear. Aim: to assess the validity of the MAS. Methods: spasticity was clinically graded using MAS and RPM measured biomechanically in the impaired arm of 111 patients following stroke. The biomechanical device measured RPM, applied force, angular displacement, mean velocity, passive range of movement ( PROM) and time required. Results: the median age was 72 years, and 66 subjects were male. The clinical grading by MAS was '0' in 15, '1' in 15, '1+' in 14, '2' in 13, '3' in 43 and '4' in 11. There was no difference in RPM among '0', '1', '1+' and '2' ( P > 0.1). However, grade '4' was higher than '3' and below (P < 0.05). The force required increased with the increasing MAS while velocity and PROM decreased (P < 0.01). We regrouped the data using the algorithm: no stiffness = '0'; mild = '1' and '1+' and '2'; moderate = '3'; severe = '4'. There was no difference between 'no stiffness' and 'mild' (P > 0.10), but 'mild' and moderate' as well as 'moderate' and 'severe' were different (P < 0.01). Conclusion: the MAS is not a valid ordinal level measure of RPM or spasticity. Objective measurement of RPM is possible in the clinical setting. However, additional measurements of muscle activity ( electromyography) will be required to quantify spasticity.