QUANTITATIVE MEASUREMENT OF SPASTICITY IN CHILDREN WITH CEREBRAL PALSY R . Price K. F. Bjornson J. F. Lehmann J. F. McLaughlin R. M. Hays Spasticity is the most common motor impairment in children with cerebral palsy (CP) (Pharoah et al. 1987) and is defined as velocity-dependent, increased resist- ance to muscle stretch (Dimitrijevic 1985). There is vigorous debate over the neurophysiological mechanism(s) that lead to spasticity. Interference with maintenance of posture and limitation of co-ordinated voluntary movement are hallmarks (Davies et al. 1977). Some affected children have learned to incorporate spasticity into essential movement strategies. Spasticity varies in severity and may affect control of few or many muscle groups. Children with the most common form of CP, spastic diplegia, have relatively greater spasticity in the lower extremities (Davies et al. 1977). Quantification of spasticity has been attempted by a variety of direct and indirect means (Katz and Rymer 1989). Clinical estimates are semi-quantitative at best (Bohannon and Smith 1987). Quantification by mechanical methods, using sinusoidal oscillations of the foot to produce a spastic response, has been discussed in the literature (Rack et al. 1984, Rebersek et al. 1986, Lehmann et al. 1989). Typically a sinusoidally time- varying angular displacement of the limb is imposed at various frequencies, ranging from 0.1 to 1 5 ~ ~ . The torque response is measured and compared with the input displacement. Rack et al. (1984) and Lehmann et al. (1989) used Fourier analysis techniques to measure the amplitude and phase shift of the torque waveform, relative to the displacement waveform, to characterize spasticity. This paper focuses on the mechanical measurement of spasticity in children with CP and compares the results with those for unaffected children and adults. Our aim is to provide a basis for the quantitative diagnosis of spasticity, as well as to provide a means of evaluating existing and novel therapies used to treat spasticity in children. In addition, knowledge of the differences in passive visco-elastic properties between adults and children can be used to account for any influence of ageing when tracking changes in individuals over an extended period from childhood to adulthood. Method The spasticity measurement system (SMS) developed at the University of Washington was designed to characterize the response of the ankle to a passive, contrclled stretch of the gastro-soleus- Achilles tendon unit. A major short- coming of clinical tests of spasticity such as the pendulum test, the tendon tap test, or the Ashworth scale is that the stimulus is not well controlled and the output is If) If) If) m If) cn 3 3 585
Transcript
QUANTITATIVE MEASUREMENT OF SPASTICITY IN CHILDREN WITH CEREBRAL PALSY
R . Price K . F. Bjornson J . F. Lehmann J. F. McLaughlin R . M. Hays
Spasticity is the most common motor impairment in children with cerebral palsy (CP) (Pharoah et al. 1987) and is defined as velocity-dependent, increased resist- ance to muscle stretch (Dimitrijevic 1985). There is vigorous debate over the neurophysiological mechanism(s) that lead to spasticity. Interference with maintenance of posture and limitation of co-ordinated voluntary movement are hallmarks (Davies et al. 1977). Some affected children have learned to incorporate spasticity into essential movement strategies. Spasticity varies in severity and may affect control of few or many muscle groups. Children with the most common form of CP, spastic diplegia, have relatively greater spasticity in the lower extremities (Davies et al. 1977).
Quantification of spasticity has been attempted by a variety of direct and indirect means (Katz and Rymer 1989). Clinical estimates are semi-quantitative at best (Bohannon and Smith 1987). Quantification by mechanical methods, using sinusoidal oscillations of the foot to produce a spastic response, has been discussed in the literature (Rack et al. 1984, Rebersek et al. 1986, Lehmann et al. 1989). Typically a sinusoidally time- varying angular displacement of the limb is imposed at various frequencies, ranging from 0.1 to 1 5 ~ ~ . The torque response is
measured and compared with the input displacement. Rack et al. (1984) and Lehmann et al. (1989) used Fourier analysis techniques to measure the amplitude and phase shift of the torque waveform, relative to the displacement waveform, to characterize spasticity.
This paper focuses on the mechanical measurement of spasticity in children with CP and compares the results with those for unaffected children and adults. Our aim is to provide a basis for the quantitative diagnosis of spasticity, as well as to provide a means of evaluating existing and novel therapies used to treat spasticity in children. In addition, knowledge of the differences in passive visco-elastic properties between adults and children can be used to account for any influence of ageing when tracking changes in individuals over an extended period from childhood to adulthood.
Method The spasticity measurement system (SMS) developed at the University of Washington was designed to characterize the response of the ankle to a passive, contrclled stretch of the gastro-soleus- Achilles tendon unit. A major short- coming of clinical tests of spasticity such as the pendulum test, the tendon tap test, or the Ashworth scale is that the stimulus is not well controlled and the output is
If)
If)
If)
m If)
cn
3 3
585
C .-
L 0
e, .- I
I I .* m 5
586
In I A -w+ Spring
Frequency
I ,-<-A Damper
B
1
Frequency C
Spring & Damper I -
-
Elastic Stiffness
Fig. 1. Stvfness response of idealized mechanical elements to sinusoidal displacements over spectrum of frequencies: (a) spring element. (b) damper element, (c) spring element in parallel with damper element.
difficult to quantify. The SMS applies a precise displacement to the foot in the form of a sinusoidal oscillation, the frequency of which can be varied. The resulting torque response of the foot moving about the ankle is measured. Torque is simply the product of force and the perpendicular distance to the force relative to the point of rotation; it is
measured in Newton-meters. The amplitude and phase-shift of the torque signal relative to the displacement signal for each frequency applied to the foot is computed using Fourier analysis. In short, the frequency response of the calf- ankle-foot system to sinusoidal dis- placement about the ankle joint is what is determined by the device. Since a spastic ankle may behave differently from a non- spastic ankle subjected to passive stretch, the frequency responses should be different for the two.
The relaxed, passively displaced calf- ankle-foot system can be crudely modelled, in mechanical terms, as a torsional spring, torsional viscous damper and rotary mass connected in parallel. The torsional elements are appropriate, since the system is being rotated. The torsional spring represents the elasticity of the gastroc-soleus-Achilles tendon unit. The torsional viscous damper represents the resistive losses of the same tissues. The rotary mass represents the mass of the foot rotating about an idealized ankle pivot joint. The application of sinusoidal displacement to such a passive visco- elastic system will produce a characteristic torque response, which is dependent on the particular mechanical properties of the model’s components. The total torque response will be the sum of torque responses from each mechanical element (for linear properties of the spring, damper and mass). The torsional spring element will contribute a torque response in phase with the displacement, with an amplitude that is dependent on the amplitude of the displacement and the stiffness of the spring. For large sinusoidal displacement amplitudes and constant torsional stiffness, a large sinusoidal torque response will result. The magnitude of the torque response of the spring is independent of the frequency of the sinusoidal displacement. The stiffness of the spring (i.e. the elastic stiffness) can be computed by dividing the spring’s torque amplitude by the displacement amplitude. If the spring’s stiffness is plotted against the frequency of a sinusoidal displacement applied to the spring, the stiffness will not vary with frequency, resulting in a frat frequency response (Fig. 1A).
The second element of the model, a torsional viscous damper, produces a resisting force in proportion to the velocity applied to it and the viscosity of the damper. The torque response of the damper (viscous stiffness) will be linearly related to the frequency of the displace- ment sinusoid. The damper will have a linearly increasing frequency response when the viscous stiffness is plotted against the frequency of the perturbing displacement (Fig. 1 ~ ) . This is because the speed across the damper is proportional to the frequency of the sinusoidal displacement applied to the damper, therefore the torque and stiffness responses of the damper will also be proportional to the frequency of the displacement applied to the damper.
The torque contribution of the rotating mass element of the model is proportional to the acceleration applied to it and its rotational inertia. For a sinusoidal displacement, the acceleration is pro- portional to the square of the frequency of the applied displacement. The torque contribution of the mass can be readily computed and subtracted from the total response, thereby leaving only the elastic and viscous responses of the system under study. The elastic and the viscous stiffness, both plotted against frequency, can each be used to characterize the response of the system.
Alternatively, the viscous and elastic stiffness for varying frequencies of the displacement input can be plotted together to yield a visco-elastic stiffness vector, with the elastic stiffness being the abscissa and the viscous stiffness the ordinate. For a linear, passive visco- elastic system with fixed elastic and viscous properties, this stiffness vector will trace out a vertical line, moving upward with increasing frequency (Fig. Ic). This behavior is due to both the fixed elastic stiffness response and the linearly increasing viscous stiffness with increasing frequency. The response of a relaxed, normal individual tested with the SMS fits this model well.
For the patient with spasticity, the behavior of the visco-elastic stiffness vector is very different, with both elastic and viscous stiffness responses varying non-linearly with frequency. The visco-
VlSCOUS STIFFNESS
I
viscous - COMPONENT
I e(,( PATH LENGTH
ELASTIC STIFFNESS
( ELASTIC COMPONENT
Fig. 2. Visco-elastic stiffness plane and demonstration of path-length generation with increasing frequency. (With permission from Lehmann et al. 1989).
elastic stiffness plot will often appear as a distorted 'c'. A single, quantitative descriptor of this visco-elastic frequency response is the path length, which is simply the distance around the 'c' (Fig. 2). In a previous report by Lehmann et al. (1989), the path length for adults with spasticity was significantly longer than that for unaffected adults. In addition, a computer-based mechanical model of the calf-ankle-foot system featuring a reflex- loop active element demonstrated that path lengths increased with increasing gains of the reflex-loop element.
In essence, the path length is a measure of the variation in visco-elastic stiffness over a range of frequencies. For a relaxed, normal individual, the variation in visco- elastic stiffness with frequency is relatively slight (resulting in a short path length), whereas for a patient with spasticity the variation is greater (resulting in a longer path length). The increase in path length is presumed to be due to spasticity. This was confirmed in the original investigation by Lehmann et al. (1989); using temporary nerve blocks in spastic patients, they demonstrated a marked reduction in path length post-block.
Sample Nine children (mean age 9.1 years, range four to 12) with spastic cerebral palsy, all patients of the authors, were evaluated. Five were girls. All had significant velocity-dependent spasticity (and no
m v,
m m
4
5
587
i
E e 3 2 u E .-
588
other movement disorders, e.g. athetosis, ataxia), as evidenced by abnormal resistance to ranging of the legs and hyperactive Achilles tendon reflexes. They were selected to represent a wide range of physical size, developmental maturity and apparent degree of spas- ticity. In cases of asymmetric spasticity, the side that appeared to be most severely affected was selected for evaluation with the SMS. This measurement requires that patients have a minimum of a 5" range of motion, with a maximum plantarflexion contracture of 2.5" from the neutral position with the leg maximally extended in prone.
For comparison, 11 unaffected children (mean age 8 - 4 years, range five to 13) and 10 unaffected adults (mean age 25.5 years, range 20 to 37) were also tested. Two of the unaffected children were siblings of children with CP and the others were children of or acquaintances of the staff. Children in both groups were of middle socio-economic status from the three-county area around Seattle. All were Caucasian, except for one oriental child in the group with CP. All children were at the age at which mature walking is established when motor development is normal (Sutherland et al. 1988). One child with CP had severe sensorineural hearing- loss, but communicated adequately using hearing aids and manual sign language; another had mild mental retardation and one had borderline intellectual function. The comparison children were intel- lectually normal. Four of the comparison children were male, seven were female. All were volunteers and were able to complete the testing without discomfort or distress, either immediately of at follow-up. Parents and experienced pediatric physical therapists known to the children were present during testing to provide reassurance.
The unaffected adult volunteers were University of Washington students and staff members. Five were male and five female. They were recruited for a parallel study, still in progress, of the comparison of mechanical and electrophysiological measures of spasticity.
Measurement technique Ankle-joint stiffness was measured with
the SMS, as described by Lehmann et al. (1989) (Fig. 3 ) . Briefly, the device measures the torque resistance produced at the ankle joint in response to a controlled sinusoidal oscillation through a 5" arc, applied at integral frequencies from 3 to 12Hz. The influences of foot and foot-plate inertia and frictional drag are eliminated to yield the elastic and viscous stiffnesses (Lehmann et al. (1989).
Subjects lie prone on the plinth to which the SMS is attached, and are asked to relax completely. Compliance was monitored by an electromyograph with surface electrodes attached to the tibialis anterior and gastrocnemius-soleus. In order to elicit the maximum spastic response from the muscle, the bias angle about which the foot was oscillated was selected so as to approach as closely as possible the maximum dorsiflexing angle available (thus producing maximum stretch). The five fixed-bias angles (i.e. midpoint of oscillation) available were 5" and 2.5" plantarflexion, and O", 2.5" and 5" dorsiflexion.
In an earlier study of spastic and unaffected adults by Lehmann et al. (1989), temporary lidocaine tibia1 and peroneal nerve blocks were performed on the group of volunteers with spasticity in order to eliminate the influence of the spastic response on the calculation of the inertial constant. This procedure was deemed unacceptable in the present study, since it would greatly diminish the willingness of children to participate. An estimate of the inertial constant for each child was based on the linear fit of the total elastic stiffness vs. square of frequency relationship (Fig. 4). This relationship is dictated by Newtonian mechanics for a sinusoidal oscillation. The slope of this linear curve is the inertial constant. In the ideal case, the experimental data would fall along a straight line and possess a correlation coefficient (r) of 1 -0. With the addition of a spastic response, the line deviates from a straight one, so the correlation coefficient is reduced to varying degrees. The r value for each individual is based on 30 data points. Data from all individuals possessed an r of 0.998 or greater, and were assumed to allow an adequate
EMG MACHINE
COMPUTER
Fig. 3. Spasticity measurement system schematic. (With permission from Lehmann et al. 1989.)
estimate of the inertial constant without nerve blocks, even though spasticity was present.
In order to test this assumption, a sample of 16 adults with spasticity (accumulated over months of clinical evaluations, during which nerve blocks were performed) was selected and the inertial constant compared, with and without nerve blocks. This sample was limited to those demonstrating an r of 0.998 or greater (consistent with the assumption that this would result in minimal error) in the computation of inertia without nerve blocks. A linear regression analysis was performed to determine the relationship between the inertial constants derived before and after nerve blocks in these adults (Fig. 5) .
Using the linear equation governing Figure 5 and the ‘estimated’ inertial constant, a ‘corrected’ inertial constant was computed for the children with CP (simulating a nerve block condition). Next the path lengths were calculated, using both the ‘corrected’ and the ‘estimated’ inertial constants. Table I indicates the
SQUARE OF FREQUENCY ( H A 0 ~ 25 50 75 100 125 150
\ -100 I \
ELASTIC
STIFFNESS .2001 \ -400 J
Fig. 4. Influence of foot plate and foot inertia on elastic stiffness for unaffected patients. (With permission from Lehmonn et al. 1989.)
differential in path length using these two methods of determining the inertial constant. It can be seen that the differential is small in comparison with the difference between spastic and unaffected groups. For unaffected child- ren, inertial constants were calculated with high accuracy (r > 0.9995) since very little, if any, reflex response occurred.
Because of the small differentials demonstrated above, path lengths were computed based on the ‘estimated’
m m
589
i
k
TABLE I Path lengths derived by estimated and corrected inertial constants for children with CP
*Based on regression equation (see text): corrected inertia= 1.0977 x (estimated inertia) -0.00582.
y=-0.00582 + 1.0977~ R2 = 0.826
4 5 6 7 8 9 ~ 1 0 . ~ Rotational inertia
without nerve block (Nrn-sec* had)
Fig. 5. Linear regression plot of inertial properties, computed with and without temporary nerve blocks in adults with spasticity.
inertial constant for children with CP, unaffected children and unaffected adults. To test for differences between these groups, the Mann-Whitney u test was used, since the results might not conform to a normal distribution.
Since the unaffected individuals dis- played little or not reflex response, it was possible to determine their passive visco- elastic properties (i.e. mechanical proper- ties present in a relaxed state). This was not possible for the children with CP because of their reflex responses and our desire to avoid nerve blocks. As demon- strated by Lehmann et af. (1989), the passive response of the ankle joint can be mathematically modelled as a linear visco-
elastic mechanical system, consisting of an elastic spring element, a linear damping element and a constant friction element, all in parallel (representing the muscle), in series with a high modulus elastic spring element (representing the tendon). In order to calculate the visco- elastic constants of these mechanical elements in unaffected children and adults, linear regression analysis was performed on the data obtained from each group.
Results Plots of typical outputs for a child with CP and an unaffected child are presented in Figure 6. The torque signal plotted is the raw torque, which includes all inertial and frictional components. Reflex activity (as indicated by the presence of a phasic EMG response) occurred in 95 per cent of trials in the group with CP and in 2 per cent of the trials for the unaffected children.
The median path length for the children with CP was 19-88 Nm/rad (range 16.42 to 73.84) and was 9.24 Nm/rad (range 4.13 to 13.99) for the unaffected children (Mann-Whitney u = 0; p < 0.001) (Table 11). Figure 7 shows typical examples of the visco-elastic response of an unaffected child and a child with spasticity. The median path length for the unaffected children was 9-24 Nm/rad (range 4-13 to 13-99) and for the unaffected adults was 12.31 Nm/rad (range 7.86 to 25-18).
D i s p l a c e n e n t ( d e w ) / Tine ( M S ) T
Torque (N-M) / Tine ( M S )
4 .80 P
188. 300, 508. 700, 980
Disu lacenent (decrs) / Tine ( M S )
-208, j : , , , : , , , 104. 388. 588. 788. 900.
'0
Ifl
Ifl 00 Ifl
m
( b )
Fig. 6. Computer-recorded displacement, torque and EMG output recorded at 7Hz for (a) unaffected child and (b) child with CP. EMG-MG is electromyographic signal of gastrocnemius muscle. EMG-TA is electromyographic signal of tibialis anterior. Positive displacement is dorsiflexion; positive torque is plantarflexing torque by patients.
Statistical analysis indicated a significant difference between the two groups (Mann-Whitney ~ = 8 7 - 0 ; p=O.O24) (Table 11).
The passive visco-elastic properties measured in unaffected children and adults are shown in Table 111. The elastic stiffness, viscosity and frictional com- ponents were all significantly larger for the adults.
Discussion Qualitatively, the response of children with CP is similar to that of the spastic adults tested by Lehmann et al. (1989). There is a frequency-dependent visco- elastic response, in combination with phasic EMG output. In the unaffected child, the frequency and amplitude of stretch is not sufficient to elicit an EMG response, except in a few isolated cases. 591
i .. .p 4
C e a 3 V C .-
Q- 0
TABLE I1 Path length values for children with CP and unaffected children and adults
Children Path length Unaffected Path length Unaffected Path length with CP (Nmhad) children (Nmhad) adults (Nmhad)
Mann-Whitney U probability: *comparison between children with C P and unaffected children, U = 0, p<O*OOI; **comparison between unaffected children and adults, U = 87, p = 0.024.
TABLE 111 Passive visco-elastic properties of unaffected children and adults
Fig. 7. Visco-elastic stiffness plane plot comparing response of child with CP and of unaffected child. Integral frequencies from 3 to 12Hz are shown. Path lengths in Nmhad indicated by 'p'.
The method of estimating the inertial properties without the aid of a temporary nerve block (see Table I) appears valid, since the error is unsystematic and small in comparison with the difference between the children with CP and the unaffected children. This method relies on linear extrapolation of the data for adults and therefore depends on the validity of such an assumption.
Path length clearly distinguishes spastic and normal muscles, as evidenced by the statistical difference between the children with CP and unaffected children. Path length is a measure of the variation of elastic and viscous stiffness over a spectrum of frequencies and is virtually
TABLE IV Comparison of elastic component of path length
Children Elastic Unaffected Elastic Unaffected Elastic with CP path length children path length adults path length
Mann-Whitney U probability: *comparison between children with CP and unaffected children, U = 0, p < 0.001; **comparison between unaffected children and adults, U = 46, p=0.526.
independent of increases in passive elastic properties that can occur as the result of contracture (Lehmann et al. 1989). The path length can be correlated with the gain of the reflex response in a mathematical model of spasticity (Rack et al. 1984, Lehmann et al. 1989), although a decreased reflex theshold may also play a role in spasticity (Powers et al. 1988).
A significant difference in path length was found between unaffected children and adults; the key to understanding this difference lies in the passive tissue properties. In a comparison of the passive visco-elastic properties of unaffected children and adults, a difference does exist. The increases in stiffness for the adults may be related to their larger muscle bulk and differing geometrical configuration and/or intrinsic changes in the tissues due to ageing. Although path- length is minimally influenced by the elastic stiffness component (due to its minimal frequency dependence), the viscosity (slope of viscous stiffness vs. frequency) may contribute significantly to the path length and therefore primarily accounts for the differences between unaffected adults and unaffected children.
These differences may become important in a long-term study of spasticity or passive properties of individual children. A long-
term increase in path length, without an increase in the underlying spasticity, may occur as the result of ageing. A spasticity measure which is insensitive to the age- dependent passive properties is needed to allow long-term study of children. One solution to this problem would be the computation of a modified path length that would feature the influence of the elastic stiffness only. This would be advantageous because, although the passive elastic stiffness increases between childhood and adulthood, this quantity is minimally frequency-dependent and contributes little to the path length in comparison with the passive viscous properties. A potential disadvantage would be that the sensitivity of the spasticity measure would be diminished, since the path length contri- bution of the viscous quantities beyond those arising from passive viscous properties may be significant for spasticity.
In a test of this potential solution, the path length was recalculated for all three populations, based on the variation in elastic stiffness only with frequency (Table IV). A Mann-Whitney u com- parison showed that a significant dif- ference still exists between children with CP and unaffected children using this modification. Yet no significant dif- ference is evident in the comparison of the unaffected adults and unaffected 593
C 2 a B u C .- x 0 * .- .- .a
3 a v1 c 0
0
m .- .a
.a
.a .- m (3
594
children. These findings support the contention that using only the elastic component of the path length eliminates the age dependency, yet maintains sensitivity to spasticity. This technique therefore allows comparison of long-term spasticity changes, regardless of the effects of ageing.
The bias or midpoint angle of the oscillation may be adjusted for each individual in order to stretch the ‘calf maximally. This in turn most likely influences the passive elastic stiffness. To the extent that the passive elastic stiffness does not change its frequency-independent characteristics but only its magnitude for various bias angles, the elastic component of the path length should still be a valid measure, since it is insensitive to the magnitude of passive elastic stiffness. This situation is analogous to higher passive elastic stiffness values for adults compared with children. By this reasoning, it should be possible to track the progress, for example, of a patient with spasticity over a period in which the bias angle is changed because of a change in range of motion. It is possible that variations in viscous stiffness may occur because of bias angle changes; however, this would be an issue only when com-
SUMMARY
puting path length in the conventional way, which incorporates both elastic and viscous stiffness components.
We conclude that the SMS can be used to measure spasticity in children with cerebral phlsy. There was a statistically significant difference between unaffected children and children with cerebral palsy. A method was developed to circumvent the use of temporary nerve blocks to calculate inertial properties in persons with spasticity. Passive elastic stiffness, viscosity and friction were found to be higher in unaffected young adults than in unaffected children. A revised path- length measure, based on elastic response only, was developed which greatly minimizes the effects of age, yet maintains sensitivity to spasticity.
Accepted for publication 5th February 1991.
Authors’ Appointments *R. Price, M.S.M.E.; K. F. Bjornson, M.S., P.T.; J. F. Lehmann, M.D.; J. F. McLaughlin, M.D.; R. M. Hays, M.D.; Departments of Rehabilitation Medicine and Pediatrics, University of Washington, Seattle, WA.
*Correspondence to first author at Department of Rehabilitation Medicine, RJ-30, University of Washington School of Medicine, BB919 Health Sciences Building, Seattle, WA 98195.
~ ~~ ~~
Spasticity was quantified in nine children with spastic diplegia, using a sinusoidal displacement of the foot at frequencies from 3 to 12Hz. Ankle-joint stiffness was separated into elastic (energy- storing) and viscous (energy-dissipating) components. ‘Path length’ was used to represent the variation in stiffness over this frequency range. Compared with 11 unaffected children, a significant difference in path lengths was demonstrated for the children with spasticity. An age-dependent effect was demonstrated when path lengths of unaffected children were compared with those of 10 unaffected adults. A modified path-length measure is proposed which minimizes age dependency, yet enables detection of spasticity. Passive stiffness properties of unaffected adults showed higher elastic stiffness, viscosity and friction than unaffected children. A method was developed to evade the need for temporary nerve blocks to calculate inertial properties of the foot in persons with spasticity.
Mesure quantitative de la spasticitd chez I’enfants I.M.C. La spasticite a 6tC quantifiee chez neuf enfants prtsentant une dipltgie spastique, a l’aide d’un deplacement sinusoi’dal du pied a des frkquences de trois a 12 Hz. La raideur de I’articulation de cheville a etC sCpar6e en composante Clastique (energie conservee) et composante visqueuse (tnergie dissipte). L’Wendue de course’ a 6tt utilisCe pour traduire la variation de raideur sur l’echelle de frequence. Par comparaison avec 1 1 enfants indemnes, une difference significative d’etendue de course a CtC observCe chez les enfants spastiques. Un effet d’tige a Cttc dtmontrtc lorsque I’Ctendue de course des enfants indemnes a ttk comparke a celle de 10 adultes indemnes. Les auteurs proposent une mesure modifte de I’etendue de course qui minimise I’influence de lage et aprtcie neammoins la spasticite. Les particularitCs de raideur passive chez les adultes indemnes rtvelaient une raideur Clastique, une viscositC et des frottements plus importants que chez les enfants indemnes. Les auteurs ont developpC une mkthode permettant d’tviter une paralysie temporaire des nerfs pour calculer les particularitts d’inertie du pied chez les spastiques.
ZUSAMMENFASSUNG Quantitative Messung der Spastik bei Kindern rnit Cerebralparese Bei neun Kindern mit spastischer Diplegie wurde die Spastik durch sinusoidale Verlagerungen des
RBSUMB
FuRes bei Frequenzen von 3 bis 12Hz quantitativ gemessen. Die Steifheit im Knochelgelenk wurde in eine elastische (Energie speichernde) und eine viskose (Energie verbrauchende) Komponente unterteilt. Die ‘Weglange’ zeigte Veranderungen der Steifheit in diesem Frequenzbereich. Im Vergleich zu 11 gesunden Kindern fand sich fur die spastischen Kinder ein signifikanter Unterschied bei den Weglangen. Beim Vergleich des Bewegungsspielraums bei gesunden Kindern und 10 gesunden Erwachsenen konnte eine Altersabhangigkeit festgegestellt werden. Die Autoren schlagen einen modifizierten Parameter fur den Bewegungsspielraum vor, der die Altersabhangigkeit reduziert, aber die Erkennung der Spastik ermoglicht. Die passive Steifheit gesunder Erwachsener zeigte mehr elastische Steifheit, Viskositat und Reibung als die der gesunden Kinder. Es wurde eine Methode entwickelt, bei der kurzfristige Nervenblokaden zur Beurteilung der Bewegungseinschrankungen des FuRes bei Patienten mit Spastik nicht notwendig sind.
RESUMEN Medicion cuantitativa de la espasticidad en niiios con paralisis cerebral Se cuantifico la espasticidad en nueve niilos con diplejia espastica utilizando un desplazamiento sinusoidal del pie a frecuencias de 3 a 12 Hz. La rigidez de la articulacion del tobillo se separo en dos componentes diferentes:elastico (almacenador de energia) y viscoso (gastador de energia). Se utilizo la longitud del camino para representar la variacion en la rigidez sobre su margen de frecuencia. En comparacion con 11 niilos no afectados se observo una significativa diferencia en la longitud del camino en niilos con espasticidad. Se observo un efecto dependiente de la edad, cuando las longitudes del camino en 10s niiios no afectados se compararon con 10s de 10 adultos no afectados. Se propone un parametro modificado de la longitud del camino que minimiza la dependencia de la edad, manteniendo la deteccion de la espasticidad. Las propiedades pasivas de la rigidez en adultos no afectados mostraron una rigidez elastica mayor, asi como mayor viscosidad y friccion que en niilos no afectados. Se desarrollo un metodo para evitar la necesidad del bloqueo temporal de nervios para calcular las propiedades de inercia del pie en personas con espasticidad.
References Bohannon, R. W., Smith. M. B. (1987) ‘Interrater
reliability of a modified.Ashworth scale of muscle spasticity.’ Physical Therapy, 67, 206-207.
Davies, P. A., Drillien, C. M., Foley, J., Bryant, K. M., Nash, M: I., Egan, J . M. (1977) ‘Cerebral palsy.’ In Drillien, D. C., Drummond, M. B. (Eds.) Neurodevelopmental Problems in Early Childhood. Oxford: Blackwell Scientific.
Dimitrijevic , M. R. (1985) ‘Spasticity.’ I n Swash, M., Kennard, C. (Eds.) ScientificBasis of Clinical Neurology. Edinburgh: Churchill Livingstone.
Katz, R. T., Rymer, W. Z. (1989) ‘Spastic hypertonia: mechanisms and measurement .’ Archives of Physical Medicine and Rehabilitation, 70, 144-155.
Lehmann, J . F., Price, R., de Lateur, B. J., Hinderer. S.. Travnor. C. (1989) ‘SDasticitv: quantitative measurements as abasis for kes s inp the effectiveness of therapeutic intervention. Archives of Physical Medicine and Rehabilitation,
70, 6-15.
Pharoah, P. 0. D., Cooke, T., Rosenbloom, I., Cooke, R. W. I. (1987) ‘Trends in birth prevalence of cerebral palsy.’ Archives of Disease in Childhood, 62, 319-384.
Powers, R. K., Marder-Meyer, J., Rymer, W. Z. (1988) ‘Quantitative relations between hypertonia and stretch reflex threshold in spastic hemiparesis.’ Annals of Neurology, 23, 115-124.
Rack, P. M. H., Ross, H. F., Thilmann, A. F. (1984) ‘The ankle stretch reflexes in normal and spastic subjects.’ Brain, 107, 637-654.
Rebersek, S., Stefanovzska, A., Vodovnik, L., Gros, N. (1986) ‘Some properties of spastic ankle joint muscles in hemiplegia. Medical and Biological Engineering and Computing, 24, 19-26.
Sutherland, D. H., Olshen, R. A., Biden, E. N., Wyatt, M. P. (1988) The Development of Mature Walking. Clinics in Developmental Medicine, Nos. 104/105. London: Mac Keith Press with Blackwell Scientific; Philadelphia: Lippincott.
