The unreliability of clinical measures of muscle tone: implications for stroke therapy

Background: the central tenet of the neurofacilitatory approach to stroke t herapy is that muscle tone needs to be normal before normal movement can oc cur. A reliable clinical measure of the full spectrum of muscle tone is nee ded to test: (i) the purported relationship between muscle tone, other moto r impairments and disability and (ii) the effectiveness of stroke therapy t o restore movement. Aim: the purpose of the study was to test the inter-rater reliability of cl inical categorization of muscle tone (spastic/normal/flaccid) and also a vi sual analogue scale with anchor points of 'lowest tone possible' (score 0) and 'highest tone possible' (score 100). Methods: four independent raters assessed tone of elbow flexors and knee ex tensors of 14 stroke rehabilitation inpatients using the categorical scale. Six independent raters assessed tone of elbow flexors and knee extensors o f 25 chronic stroke patients and two healthy volunteers using the visual an alogue scale. All assessment orders were randomized. Results: both scales were unreliable, with k coefficients for the categoric al scale ranging from -0.046 to 0.56 for the categorical scale, and intracl ass correlation coefficients for the visual analogue scale of 0.595 for elb ow flexors and 0.451 for knee extensors. Assessment order effects for the v isual analogue scale were non-significant for elbow flexors (P = 0.545) and knee extensors (P = 0.911). Conclusions: these results, and those of earlier studies, suggest that clin ical measures of muscle tone are consistently unreliable. Systematic invest igation of the therapy rationale for planning and evaluating treatment is r equired before relevant clinical measures can be developed.