The construct validity of a spasticity measurement device for clinical practice: An alternative to the Ashworth scales

Introduction. Spasticity is a significant cause of disability in people with an upper motor neurone lesion, but there is a paucity of appropriate outcome measures to evaluate this phenomenon. The aim was to test the construct validity of a clinically relevant, non-invasive measure of spasticity. Methods. A cross-section study design in which participants with elbow flexor spasticity and capable of providing written informed consent were recruited. Results. Fourteen stroke patients participated (six female and eight male). Median age was 61 years and the median time post stroke was 48 months. Six patients had a MAS grading of '1+', three a grade of '2' and five a grade of '3'. The velocity of the brisk stretch was significantly higher than that of the slow stretch (p < 0.05: median difference, 34 degrees/s: IQR, 20-46). Flexor muscle activity during the brisk stretch was significantly higher than that of the slow stretch (p < 0.05: median difference, 2.0 mu V; IQR, 0.4-8.4). In contrast the RPE was not significantly different between the slow and the fast stretches (p > 0.1: median difference, 0.07 N/deg; IQR, -0.09-0.16). There were no patterns of association between the MAS, elbow flexor muscle activity and RPE. Other important observations, in some patients, were: continuous background muscle activation consistent with descriptions of spastic dystonia; muscle activity at the slow velocity stretch; muscle activation patterns consistent with the clasp-knife phenomenon. Conclusions. The measurement system was capable of measuring spasticity as defined by Lance (1980; In: Lance et al., editors. Spasticity: disordered motor control. Chicago, IL: Year Book. p 185-204). In addition, it enabled various other clinical phenomena associated with spasticity to be measured. Assessing spasticity by measuring changes in resistance to passive movement only may not be sufficient, as the latter is influenced by many factors of which spasticity may only be one. Further work is now required to investigate repeatability and sensitivity.