Biomechanical and electrophysiological evaluation of spasticity

1
Biomechanical and electrophysiological evaluation
of spasticity  

• Jens Bo Nielsen, Klaus Klinge, Fin
  Biering-Sørensen, Mike Grey and Clarissa Crone
• Department of Medical Physiology and Institute of
  Exercise and Sport Sciences, University of
  Copenhagen. Department of Clinical
  Neurophysiology, Copenhagen University Hospital
  (Rigshospitalet)

Fig. 4
Fig. 2
Introduction Spasticity is defined as a
velocity-dependent increase in muscle tone
following lesion of upper motor neurons. Several
studies have pointed out that the Ashworth scale
shows high inter- and intra-rater variability and
that there is a need for developing evaluation
techniques based on quantitative biomechanical
measurements. Here we report findings from a
project with the aim of developing such a
technique.
Methods 17 healthy subjects, 15 patients with
multiple sclerosis and 15 patients with spinal
cord lesion (ASIA score B-C lesion at C5-Th12, 4
month 30 years after lesion) participated in the
study. The subjects were seated in a reclining
chair with their most affected leg attached to a
foot plate, which could be rotated by a
computer-controlled motor. Stretches (50 deg/s to
250 deg/s) were applied to the ankle
plantarflexor muscles at intervals ranging from 1
to 10 s. The torque evoked by the stretches was
measured as the peak torque at an interval of
150-300 ms after the onset of stretch. EMG
recording was obtained from electrodes placed
over the belly of the soleus muscle. In addition
H-reflexes were evoked by stimulation of the
tibial nerve. All responses were normalized to
the maximal response evoked by supramaximal
stimulation of the tibial nerve
There was no difference in the amount of
absolute torque (in Nm) evoked by the stretch at
an interval of 15 s when comparing spastic
patients and healthy subjects. However, when the
torque was normalised to the torque evoked by
supramaximal stimulation of the tibial nerve a
significant difference was found.
In both healthy subjects and all spastic patients
the H-reflex was significantly more depressed
that the stretch reflex with reduced interval
between stimuli. In the spastic patients both the
H-reflex and the stretch reflex were less
depressed than in the healthy subjects. In SCI
subjects the stretch reflex was thus not
depressed at all with reduced stimulus interval.
This confirms that post-activation depression is
reduced in spastic patients and may play a
significant pathophysiological role.

• Aims
• To compare the influence of different stimulus
  intervals on the size of stretch reflexes and the
  evoked torque in healthy subjects and spastic
  patients. Previous studies have implied that the
  depression of reflexes with reduced stimulus
  interval (post-activation depression) is of
  importance for the manifestation of spasticity
  (Nielsen et al. 1993 1995).
• To investigate whether normalization of the
  stretch evoked EMG responses and torque to the
  maximal responses and torque evoked by
  supramaximal stimulation of the nerve supplying
  the muscle may reduce the inter-individual
  variability of the measurements.

Fig. 3

• Conclusion and discussion
• The findings imply
• that the interval between stretches or passive
  manipulations must be considered when evaluating
  spasticity.
• that normalization of the evoked responses and
  the measured torque to the maximal responses and
  torque evoked by supramaximal stimulation of the
  peripheral nerve supplying the muscle is
  necessary when evaluating spasticity
• that reduced post-activation depression is of
  direct significance for the increased reflex
  excitability and resistance to stretch in spastic
  patients.

Fig. 1
References Hultborn H, Illert M, Nielsen J,
Ballegaard M, Paul A Wiese H. (1996). On the
mechanism of the post-activation depression of
the H-reflex in human subjects. Experimental
Brain Research 108, 450-62. Nielsen J,
Petersen, Ballegaard M, Biering-Sørensen F
Kiehn O. (1993). H-reflexes are less depressed
following muscle stretch in spastic spinal cord
injured patients than in healthy subjects.
Experimental Brain Research 97, 173-176 Nielsen
J, Petersen N Crone C. (1995). Changes in
transmission across synapses of Ia afferents in
spastic patients. Brain. 118, 995-1004
The torque evoked by the stretch was also reduced
with reduced stimulus interval in both healthy
subjects and spastic patients. There was a
statistically significant difference in the
amount of normalized torque between spastic
patients and healthy subjects at all stimulus
interval, but the greatest difference was seen at
short stimulus intervals. This strengthens that
the amount of post-activation depression is of
direct significance for the measured resistance
to stretch in spastic patients.
Acknowledgements This study was supported by
grants from the Danish Multiple sclerosis
association and the Elsass Foundation
Example of the responses to stretch of the soleus
muscle (left) and the responses to supramaximal
stimulation of the tibial nerve (right)
P07.19 Cromdale