Quantification of muscle tone

Details Quantification of muscle tone Quantification of muscle tone

2001-09-06

2003-07-08

Hindenburg, Max F. (Department: 3736)

Surgery

Diagnostic testing

Measuring anatomical characteristic or force applied to or...

Reexamination Certificate

active

06589190

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a method and apparatus for the quantification of muscle tone. More particularly, the present invention relates to a method and device that utilize non-sinusoidal perturbations to quantify muscle tone. The device is, and method are particularly useful in quantifying muscle tone in a spastic patient.
BACKGROUND OF THE INVENTION
Individual skeletal muscle cells are mechanically and anatomically arranged in parallel. The total force produced by a muscle is equal to the sum of the forces generated by its constituent cells. In the normal subject, muscles that comprise the wrist flexors and extensors are normally relaxed and are usually recruited to generate force and movement.
Lower motor neuron paralysis occurs when muscles are deprived of their immediate nerve supply from the spinal cord. This occurs when a nerve between the spinal cord and a muscle is cut or when cell bodies of the ventral horn are destroyed as in poliomyelitis. Muscles become soft and atrophic, and reflex response to sensory stimuli is lost. Most nerve disorders that affect limb function are due to upper motor neuron paralysis, wherein damage is present somewhere in the corticospinal tract that originates in the brain and travels through the spinal cord.
Spasticity is defined as abnormal involuntary contraction of a muscle or group of muscles due to a rate-dependent reflex mechanism. The spindle elicits the reflex response upon deformation. To a certain extent, these reflexes are normal and important. In normal operation, these reflexes are suppressed to a certain extent to allow flexibility and motion of joints. In spasticity however, there is a disruption in the normal behavior of the stretch reflex that causes muscles, particularly the flexors, to be extremely resistive to passive stretch (i.e. high in tone). As a result, motor control is severely impaired and stiffness or tightness of the muscles may interfere with gait, movement, and speech. Spasticity is usually found in people with some sort of upper motor neuron paralysis, such as those with cerebral palsy, traumatic brain injury, spinal cord injury and stroke patients.
Common symptoms of spasticity may include hypertonicity (increased muscle tone), clonus (a series of rapid muscle contractions), exaggerated deep tendon reflexes, muscle spasms, scissoring (involuntary crossing of the legs) and fixed joints. The degree of spasticity varies from mild muscle stiffness to severe, painful, and uncontrollable muscle spasms. The condition can interfere with rehabilitation in patients with certain disorders, and often interferes with daily activities.
Many forms of intervention are available to reduce muscle tone in spasticity. Biochemical pharmaceuticals such as Botox (Botulinum Toxin Type A), Intrethecal Baclofen, and Zanaflex (tizanidine) may be used as a biochemical form of intervention. (See R. W. Armstrong, P. Steinbok, D. D. Cochrane, et al.
Intrathecally administered baclofen for treatment of children with spasticity of cerebral origin
. J Neurosurg; 87(3):409-414, Sep 1997; J. V. Basmajian, K. Shankardass, D. Russel:
Ketazolam Once Daily for Spasticity: Double
-
Blind Cross
-
Over Study
. Arch. Phys. Med. Rehabil. Vol. 67, pp556-557, 1986; P. J. Delwaide:
Electrophysiological Analysis of the Mode of Action of Muscle Relaxants in Spasticity
. Annals of Neurology, Vol. 17, No. 1, January 1985, pp 90-950). These chemicals are used either to destroy nerve endings at the neuromuscular junction, or they are used as blocking agents which depress neuromuscular transmission by competing with acetylcholine for receptors, thus suppressing nerve conduction. In severe cases, microsurgery is also an option, where incisions are made in the brainstem or anywhere in the stretch reflex pathway. The safest form of intervention is physical therapy, such as training, stretching exercises and casting. (J. C. Otis, L. Root, M. A. Kroll:
Measurement of Plantar Flexor Spasticity During Treatment with Tone
-
Reducing Casts
. Journal of Pediatric Orthopedics 5:682-686, 1985).
Tone is defined as the degree of resistance to stretch from an external source. An assessment of tone is important in evaluating the degree of spasticity that a patient has. This assessment is imperative for the clinician to decide what form of intervention to take and to what degree. Further, continued assessment throughout intervention is important to assess the effectiveness of the intervention. For example, if the Botox dosage administered is too low, it may have little or no effect in reducing a patient's spasticity. Conversely, if the dosage is too high, then the patient may lose the ability to control his or her limb, as blocking too many neuromuscular junctions at the muscle site may prevent the central nervous system from having any control over the muscle. An assessment of tone before and after intervention is also important as it can demonstrate the effectiveness of the treatment.
Probably the most widely accepted clinical test for the evaluation of tone in spasticity is the Ashworth scale shown below in Table 1.
TABLE 1
Grade
Description
0
No increase in muscle tone.
1
Slight increase in muscle tone, manifested by a catch and
release or by minimal resistance at the end of the range of
motion when the affected part(s) is(are) moved in flexion
or extension.
2
Slight increase in muscle tone, manifested by a catch fol-
lowed by minimal resistance through the remainder of the
range of motion but the affected part(s) is(are) easily
moved.
3
More marked increase in muscle tone through most of the
range of movement, but affected part(s) easily moved.
4
Considerable increase in muscle tone, passive movement
difficult.
5
Affected part(s) is(are) rigid in flexion or extension.
TABLE 1: Modified Ashworth scale. The Ashworth scale is a popular, and widely accepted method of evaluating muscle tone among clinicians. Though the grades are numeric, they are based on a qualitative “feel” of resistance to passive stretch movements performed by the clinician on the patient. (Taken from Arch. Phys. Med. Rehabili. Vol 80, September 1999).
The clinician moves the subject's limbs about the joints and then assigns a grade based on a “touchy feely” assessment of how much resistance the clinician feels. One can easily see the problem here. Since the test is a qualitative one, different clinicians may assign different grades to the same test. Even the same clinician's evaluation may change due to lack of consistency or depending on whether he or she is optimistic or pessimistic at the time of the test. The clinician may also be biased and may, for example, assign a better grade if he or she has knowledge of interventions being performed on the patient. Even putting all these issues aside, it is difficult to get an absolute measure of tone using the Ashworth scale. As stated in a review article “The quantification of spasticity has been a difficult and challenging problem, and has been based primarily on highly observer-dependent measurements. The lack of effective measurement techniques has been restrictive, since quantification is necessary to evaluate various modes of treatment.” (R. T. Katz, W. Rymer:
Spastic hypertonia; mechanisms and measurement. Archives of Physical Medicine and Rehabilitation.
1989; 70:144-145).
In attempt to quantify muscle tone, some have used Electromyography (EMG) information. (See P. J. Delwaide:
Electrophysiological Analysis of the Mode of Action of Muscle Relaxants in Spasticity
. Annals of Neurology, Vol. 17, No. 1, January 1985, pp 90-95; A. Eisen:
Electromyography in Disorders of Muscle Tone
. Le Journal Canadien des Sciences Neurologiques, Vol. 14, No. 3. August 1987, pp 501-505; W. G. Tatton, P. Bawa, I. C. Bruce, R. G. Lee:
Long Loop Reflexes in Monkeys: An Interpretative Base for Human Reflexes. Cerebral Motor Control in Man.: Long Loop Mechanisms
. Prog. clin. Neurophysiol., vol 4, Ed. J. E. Desmedt, pp 229-245, Krager Basel, 1978). EMG electrodes measure and amplify actual action potentials sent to the

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