Development and Inter-rater Reliability of an Assessment Tool for Measuring Muscle Tone in People with Hemiplegia after a Stroke

Summary

There is no validated method of measuring spasticity per se The most widely accepted clinical scale, the modified Ashworth scale, has been evaluated only at the elbow and does not take account of the possible effects of posture and associated reactions on tone. The aim of this study was to develop a reliable measure which incorporated response to passive movement, resting posture and associated reactions to active effort.

The Tone Assessment Scale was constructed and modified, and its reliability tested in 15 patients with stroke. Inter-rater comparisons were made between two physiotherapists examining the reliability of each item of the scale.

The six items reflecting response to passive movement were reliable (Kw 0.66 – 0.94), while those relating to posture were not (K 0.12 – 0.49). Only two of the three items relating to associated reactions were reliable (Kw 0.79 and 0.94, K 0.31).

The establishment of reliability of measurement of tone at a number of joints should ensure more comprehensive estimates of spasticity and facilitate determination of treatment effects.

Introduction

Spasticity is defined as a velocity-dependent increase in muscle tone with hyperactive stretch reflexes (Lance, 1976). It occurs in disorders of the central nervous system, including approximately two-thirds of patients with stroke (Wallesch et al, 1997). Along with loss of motor power and disorders of sensation and perception, spasticity is generally thought to contribute to post-stroke functional impairment. It produces abnormal posture, and is complicated by associated reactions to active effort, defined as involuntary, stereotyped movements (Davies, 1985). Much rehabilitation time, and therefore National Health Service resources, are spent in the treatment of post-stroke spasticity, and clinicians and therapists often attempt to quantify treatment effects. However, while clinicians feel the measurement of spasticity to be important (Haas, 1994), the most common method of indicating abnormal tone is a subjective grading of mild, moderate or severe (denoted on a body diagram as +, ++ or +++ respectively) (Stephenson, 1996).

While there is no validated method of measuring spasticity per se, the most widely accepted clinical scale for assessing tone is the modified Ashworth scale (Bohannon and Smith, 1987). Originally, Ashworth described a five-point scale which assessed tone of ‘the limbs' (Ashworth, 1964). This was later modified to a six-point scale (Bohannon and Smith, 1987) in the belief that two discrete levels of tone fell within a single point on the original scale. The modified Ashworth scale was originally evaluated only at a single joint, the elbow (Bohannon and Smith, 1987) and therefore is not known to be reliable throughout the body, although other investigators have assumed its usefulness at other joints (Lee et al, 1989; Sloan et al, 1992; Haas et al, 1996). Furthermore, there are no available specific written guidelines for its use. Although some physiotherapists make note of the position in which the response to passive movement was measured, it is not done in any formalised way and precludes comparison between patients or changes with time. It is not widely used in clinical practice, and this may be because it does not give a global measure of spasticity, as usually only one joint is assessed. It takes no account of the possible effects of posture and associated reactions on the measurement and functional relevance of tone.