Manual linear movements to assess spasticity in a clinical setting

Abstract

In a clinical setting, where motor-driven systems are not readily available, the major difficulty in the assessment of the stretch reflex lies in the control of passive limb displacement velocity. A potential approach to this problem arises from the use of manual sinusoidal movements (made by continuous alternating flexions and extensions) paced by an external stimulus. Unfortunately, there are conditions in which sinusoidal movements induce interfering phenomena such as the shortening reaction or postactivation depression. In the present paper, a novel manual method to control the velocity of passive linear movements is described and the results obtained from both healthy subjects and spastic patients are reported. This method is based on the synchronisation of movements with tones played by a metronome at different speeds. In a first set of experiments performed in healthy subjects, we demonstrated consistent control of velocity during passive limb movements using this method. Four joints usually examined during muscle tone assessment were tested: wrist, elbow, knee and ankle joints. Following this, we conducted a longitudinal assessment of the stretch reflex amplitude in wrist flexor muscles in patients with spasticity treated with botulinum toxin type A. The evaluators were not only able to vary the movement velocity based on the metronome speed, but also could reproduce the respective speeds two weeks later, despite the changing degree of hypertonia. This method is easy to perform in a clinical setting and hardware requirements are minimal, making it an attractive and robust procedure for the widespread clinical assessment of reflex hypertonia.

Figure 1. Experimental procedure.

During phase 4 the evaluator performs a smooth extension movement which starts and ends in synchrony with the metronome tones. The mean velocity is derived from the resulting velocity profile.

Figure 2. Mean-V in the normal subjects group has a direct linear relationship with BPM for all the tested joints according to the following functions.

Wrist: y = 1.8*x+3.8, elbow: y = 1.8*x+1.3, knee: y = 1.3*x+29.5, ankle: y = 7.9*x–15.1.

Figure 3. Mean-V in the patients group is plotted in baseline and test conditions.

The filled circles connected with dashed line represent the evaluator A, while the filled squares connected with a solid line represent the evaluator B. Mean-V is higher at 60 BPM without any difference between baseline and test conditions or between evaluator A and B.

Figure 4. The SR/M ratio is higher at baseline compared to the test condition.

The trend toward an increased SR/M at 60 BPM does not reach significance. No difference can be found between the two evaluators.