Robot controlled, continuous passive movement of the ankle reduces spinal cord excitability in participants with spasticity: a pilot study

Abstract

Spasticity of the ankle reduces quality of life by impeding walking and other activities of daily living. Robot-driven continuous passive movement (CPM) is a strategy for lower limb spasticity management but effects on spasticity, walking ability and spinal cord excitability (SCE) are unknown. The objectives of this experiment were to evaluate (1) acute changes in SCE induced by 30 min of CPM at the ankle joint, in individuals without neurological impairment and those with lower limb spasticity; and, (2) the effects of 6 weeks of CPM training on SCE, spasticity and walking ability in those with lower limb spasticity. SCE was assessed using soleus Hoffmann (H-) reflexes, collected prior to and immediately after CPM for acute assessments, whereas a multiple baseline repeated measures design assessed changes following 18 CPM sessions. Spasticity and walking ability were assessed using the Modified Ashworth Scale, the 10 m Walk test, and the Timed Up and Go test. Twenty-one neurologically intact and nine participants with spasticity (various neurological conditions) were recruited. In the neurologically intact group, CPM caused bi-directional modulation of H-reflexes creating 'facilitation' and 'suppression' groups. In contrast, amongst participants with spasticity, acute CPM facilitated H-reflexes. After CPM training, H-reflex excitability on both the more-affected and less-affected sides was reduced; on the more affected side H@Thres, H@50 and H@100 all significantly decreased following CPM training by 96.5 ± 7.7%, 90.9 ± 9.2%, and 62.9 ± 21.1%, respectively. After training there were modest improvements in walking and clinical measures of spasticity for some participants. We conclude that CPM of the ankle can significantly alter SCE. The use of CPM in those with spasticity can provide a temporary period of improved walking, but efficacy of treatment remains unknown.

Keywords: Continuous passive movement; H-reflex; Spasticity; Spinal cord excitability.

Fig. 1

A photograph of the experimental set-up when using the CPM device

Fig. 2

A graphical representation of the experimental timeline and within subject control procedures used in experiment 2 for participants with spasticity

Fig. 3

Group mean (± SE) soleus H-reflex amplitudes for the facilitation (filled) and suppression (unfilled) groups from pre- and post-CPM use are shown in (a). Group mean (± SE) for the effect of sural conditioning on H-reflex amplitudes for the facilitation (filled) and suppression (unfilled) groups from pre- and post-CPM use are shown in (b). In c, a single participant’s average of ten traces for unconditioned (dotted line) and sural conditioned (solid trace) pre- (left) and post- (right) CPM use are shown for a participant in the facilitation group (top) and a participant from the suppression group (bottom)

Fig. 4

A single participant’s pre-CPM (recorded prior to training) M-wave and H-reflexes corresponding to variables measured in the recruitment curve analysis on the MA and LA side

Fig. 5

A single participant’s pre (unfilled) and post (filled) training H-reflex recruitment curves recorded from the less affected (LA; shown in a) and more affected (MA; shown in b)

Fig. 6

Mean change in input/output characteristics of the H-reflex from the recruitment curve ascending limb following CPM training in spasticity. Filled and unfilled bars represent the more- and less-affected leg, respectively. Asterisk indicates significant difference (p < 0.05)