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Quantitative clinical measure of spasticity in children with cerebral palsy
594
Quantitative Clinical Measure of Spasticity in Children With Cerebral Palsy Jack R. Engsberg, Phi), Kenneth S. Olree, MS, Sandy A. Ross, MHSPT, T. S. Park, MD ABSTRACT. Engsberg JR, Olree KS, Ross SA, Park TS. Quantitative clinical measure of spasticity in children with cerebral palsy. Arch Phys Med Rehabil 1996;77:594-9.
Objective: This investigation developed an objective measure to quantify the degree of spasticity. Design: Specifications included a single variable that integrated key elements characterizing spasticity: velocity, range of motion, and resistance to passive motion. A dynamometer at a children's hospital quantified the passive resistance of the hamstrings to knee extension for a range of motion at 4 different speeds for the prospective descriptive investigation. Patients: A convenience sample of six children with able bodies and 17 children with spastic diplegic cerebral palsy volunteered. Data Processing: Torque-angle data were processed to calculate the work done by the machine on the children for each speed and then determine the slope of the work-velocity curves. This slope was considered to be the measure of spasticity and it was hypothesized that children with cerebral palsy would have a greater slope than children with able bodies. An independent t test determined whether a significant difference existed between groups (p < .05). Results: Torque-angle data for children with able bodies indicated little change in passive resistance as a function of speed. Similar data for children with cerebral palsy indicated larger resistive torques with increasing speed. Slope from the workvelocity data was close to zero for children with able bodies [.003 J/(°/sec)], while the corresponding slope for children with cerebral palsy was approximately 10 times greater [.031 J/(°/ sec)] and significantly different (p < .05). Conclusion: The slope of the work-velocity data integrates three major components characterizing spasticity, it is a single number that can easily be evaluated and interpreted in a clinical setting, and it utilizes a machine that is available at many centers. © 1996 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation MAJOR IMPAIRMENT in cerebral palsy is spasticity. Clinically, the term spasticity is often used to refer to a number of impairments, including muscle hypertonia, ~'2 hyperactive deep tendon reflex,3 clonus, 4 and velocity-dependent resistance to passive stretch. 5-7 Many surgical and therapeutic procedures are performed, and many pharmacological drugs are
A
From the Motion Analysis Laboratory, Department of Neurosurgery, St. Louis Children's Hospital (Dr. Engsberg, Mr. Olree, Ms. Ross, Dr. Park) and Washington University School of Medicine (Dr. Engsberg, Dr. Park), St. Louis, MO. Submitted for publication June 27, 1995. Accepted in revised form December 14, 1995. No commercial party having a direct or indirect interest in the subject matter of this article has or will confer a benefit upon the authors or upon any organization with which the authors are associated. Reprint requests to Jack R. Engsberg, PhD, Director, Motion Analysis Laboratory, St. Louis Children's Hospital, One Children's Place, St. Louis, MO 63110. © 1996 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation 0003-9993/96/7706-357453.00/0
Arch Phys Med Rehabil Vol 77, June 1996
administered to children with cerebral palsy to minimize or eliminate the influence of spasticity.8-m Methods to quantify the various types of spasticity include the Modified Ashworth scale, electromyography (EMG), deep tendon reflex tests, and resistance-to-motion t e s t s . I-4'9'tH4 Of these four methods for assessing spasticity only the Modified Ashworth scale is regularly used in a clinical setting] ~ The Modified Ashworth Scale involves manually moving a limb through the range of motion to passively stretch specific muscle groups. The scale permits a rapid assessment of the degree of spasticity about many joints. However, although its use is widespread in clinical and research settings for assessing spasticity, it remains a basically subjective measure recorded in ordinal data.l ~ As a consequence, its reliability has been called into question. 15 In contrast to the Modified Ashworth scale, the remaining three methods for assessing the degree of spasticity are objective measures. These tests, however, have limitations that prevent them for being used regularly in a clinical setting. EMG has been used to examine muscle activity in spastic adults and children undergoing selective dorsal rhizotomy surgery] 2A6Although it provides insight into the activity of the muscle, the methods are difficult to use clinically. The EMG signal is highly dependent on the techniques used to record them (eg, electrode type, electrode placement) and on the muscle under examination? Further, the relationship between EMG and muscle force is not easily quantified. Deep tendon reflex tests apply an impact load to a specific tendon and measure EMG, leg displacements, force, or acceleral i o n s . 4'13'17 Custom-made devices have been developed to standardize the impact to the tendon] 7 Nevertheless, these devices may not be applicable to other tendons, and the generalization of results to other joints is unknown. Resistance-to-motion tests seem to fail into two types. Both types assess resistance to motion with dynamometers; one type measures the resistance during small oscillations and the other measures resistance over a large range of m o t i o n . 9'14']839 In both cases the tests are not regularly used in a clinical setting. Some of these tests require custom-made equipment not available to many centers. 14'~9Some do not provide information that can be easily understood and interpreted by the clinician. TM Often the device is not applicable to a variety of joints or muscles, t'4'w The purpose of this investigation was to develop a method to quantify the degree of spasticity that would be useful in the clinical setting. Priorities for this method included equipment that was available to many centers, ease of operation, applicability to a variety of joints and muscles, and simple but meaningful results. To maintain both clinical and mechanical relevance, and to maximize simplicity of results, spasticity was characterized as a velocity-dependent resistance to passive stretch. 5-7
METHODS For this prospective, descriptive investigation, a convenience sample of six children with able bodies (mean age 9 years, range 4 to 17; 2 boys, 4 girls; mean mass 34.5kg, SD 17.9) and 17 children with spastic diplegie cerebral palsy (mean age 10 years, range 4 to 16; 8 boys, 9 girls; mean mass 32.3kg, SD 14.6) were tested. The children with able bodies were recruited
SPASTICITY MEASURE IN CHILDREN WITH CP, Engsberg
through parents within the hospital community or were siblings of children visiting the hospital. The children with cerebral palsy had been referred to the motion analysis laboratory for other testing by an orthopedic surgeon or were scheduled to undergo a selective dorsal rhizotomy the following day and were referred to the laboratory by a neurosurgeon. The clinical diagnosis of spastic diplegic cerebral palsy was made by the referring physician. Only children who were large enough to fit comfortably on the test equipment and who would presumably cooperate were approached for participation. All parents and children who were asked to participate consented. Each child and/or parent was informed about the project and gave informed consent. In each child with an able body only one leg was tested. Attempts were made to test both legs of the children with cerebral palsy, but if a child became tired, bored, or uncooperative, only one leg was tested. Initial efforts at determining the reliability of the measure were accomplished by testing two children at two different times after their selective dorsal rhizotomy surgery. One child was tested at 34 and 41 weeks after surgery and a second child was tested at 10 and 21 months after surgery. The KinCom dynamometer~can move the passive leg through a range of motion at a specified speed, measuring the force applied to a support arm during the motion. Each child sat on the KinCom with stabilization straps across the distal aspect of the thigh and pelvis. The child was supported at his or her back and was capable of maintaining an upright position. The axis of the KinCom was aligned with the knee axis of the child. The leg of the child was attached to the support arm by securing the leg against a tibia pad with Velcro straps. A fixed laboratory coordinate system was established by moving the lever arm to a horizontal position (0°). Torques were calculated by inputting the distance of the tibia pad from the rotation axis of the machine. Before conducting the spasticity tests, the anatomic range of motion limits for knee extension or hamstring length were established for each child. The starting position for the test was approximately 60 ° below the horizontal, although this position was decreased to 50 ° if substantial quadriceps resistance existed. A special feature of the KinCom was used to determine the limits for knee extension. This feature caused the machine to stop if a preset force (ie, termination force) was reached. Initially, the machine was set to take the knee of the child beyond its physiological limits. To prevent this from happening a low termination force value was programmed into the machine to stop the test. The end range of extension motion was determined by assigning a speed of 10°/sec to the KinCom and engaging the passive mode. The child was instructed not to help the lever arm move and remain as relaxed as possible as the leg rotated from a flexed to an extended position. The end range of motion for knee extension was determined and recorded by gradually increasing the termination force until the child felt uncomfortable, the pelvis began to rotate posteriorly, or the knee began to rise. The final termination force values were converted to torques for each child and ranged between 6 and 20Nm. To insure the safety of the child an adult closely observed the tests and held a button that, if pressed, would stop the test. The spasticity tests were then conducted. These tests were similar to the previous one except that the end range of extension motion was used to stop the tests instead of a termination force value. The starting angle remained at approximately 60 ° below the horizontal. The termination force was increased from its preset value to assure that the end range of motion was achieved. Tests for knee extension were conducted at speeds of 10°, 30°, 60 °, and 90°/sec, and the resistive torque was continuously monitored during the trials.
0-
595
..........
" ................
_2J v
-6"
-8"
Knee Flexed ] -lC -7o -~o -~o
4o
-5o -~o -10 KinCem Angle (degrees)
IKnee Extended 1'o ~o 30
Fig 1. Quantification of the work done (torque × angular displacement) by the KinCom machine on one subject at one speed (shaded area). The boundaries for the a r e a were the torque-angle curve, the zero torque line, and the end range of motion (about 12°). A work value was calculated for each of the four speeds for each child. Inertial and gravitational effects have been accounted for in the torque values.
The force data from each child were downloaded to a personal computer in which the weight of the leg and foot due to gravity, estimated to be 5.8% of total body weight, was partialled out in a custom computer program. 2° The acceleration of the leg from a motionless position to a constant angular velocity produced a torque component in the data that was unwanted. As would be expected this component was increased as both the speed of the test and the mass of the leg and foot increased. These inertial effects were removed by modeling the acceleration component as an underdamped second-order system and subtracting it from the torque values.2~ The areas quantifying the work done (ie, fT*d0 where T = Torque and dO is a small angular displacement measured in radians) by the machine on the child were calculated using the trapezoid rule. The boundaries for the areas were the torqueangle curve, the zero torque line, and the end range of motion (fig 1). Four areas quantifying work were determined for each child for the given speeds (ie, 10°, 30°, 60 °, 90°/sec). Linear regression was used to determine the line of best fit for these four areas as a function of speed. The slope of the linear regression line was considered to be the measure of spasticity. It was hypothesized that the children with able bodies would have slopes close to zero because they have no velocity-dependent resistance to stretch and the children with cerebral palsy would have slopes greater than zero because they do have a velocitydependent resistance to stretch. Because not all children wit~l cerebral palsy had both legs tested, the single leg tested was used in the analysis (n = 6). In the cases where both legs were tested, a single leg from each child was randomly chosen for analysis (n = 11). A chi-squared test was performed to determine if the distribution of the slopes for the children with cerebral palsy were significantly different from a normal distribution. Since no significant difference was found (p < .01) an independent t test was used to determine if a significant difference existed between the slopes for the two groups of children (p < .05). RESULTS Torque-angle data for a typical child with an able body indicated very little change in resistive torque as a function of speed
Arch Phys Med Rehabil Vol 77, June 1996
596
SPASTICITY MEASURE IN CHILDREN WITH CP, Engsberg Table 1: Work Done by the KinCom Machine on Childrens' Knees
2
Work (Joules) 0
Subjects
10°/sec
30°/sec
60°/see
90°/sec
-2-
Able body (n = 6) SD Cerebral palsy (n = 17) SD
2.81 2.48 2.81 1.92
2.78 2.35 3.82 2.40
2.91 2.12 4.22 2,30
3.04 2.11 5.52 3.04
E z -4
Means and standard deviations for the work done (ie, torque x angular displacement) by the KinCom machine on knees of the children with cerebral palsy and the children with able bodies at 4 speeds of knee extension in the upright position. The work remained relatively constant regardless of the speed for the children with able bodies. In contrast, the work for the children with cerebral palsy increased as thespeed increased.
O F--8"
I to dens
-8"
Knee Flexed } -10 -70-60 -50
[ Knee Extended -40 -30 -20 -10 KinCorn Angle (degrees)
1'0
20
30
Fig 2, Results of the passive resistance tests for a typical child with an able body (girl, age 7 years, mass 26kg). Very little difference existed between curves regardless of the speed of knee extension, indicating little relationship between resistance and speed through the range of motion. Inertial and gravitational effects have been accounted for in the torque values.
because all curves were essentially the same (fig 2). In addition, the ordering of the curves according to magnitude did not progressively increase or decrease. In contrast, similar data for a typical child with cerebral palsy indicated larger resistive torques with an increase in speed (fig 3). An extensor torque (ie, positive value) existed for about the first 20° to 25 ° of motion for both groups of children, The presence of the extensor torque before a flexor torque was common in most children. The work done (fig 1) by the machine on the knees of the children with able bodies remained relatively constant for the four speeds, whereas the work done on the children with cerebral palsy increased as the velocity increased (table 1). There was an 8% increase from the slow speed to the fast speed in the children with able bodies and a 96% increase from slow to fast for the children with cerebral palsy. The standard deviations were relatively large for both groups of children. This was because of the variability in both the point at which the curves
crossed the 0 torque line and the magnitude of the resistive torque throughout the range of motion. The slope (Joules/(°/sec)) of the linear regression line for work values as a function of velocity (table 1) for the children with able bodies was very close to zero (.0031, SD = .009), whereas the corresponding slope for the children with cerebral palsy was approximately 10 times greater (.033, SD = .019) (fig 4). These slopes were significantly different (p < .05). The repeat testing of the two groups of children after selective dorsal rhizotomy surgery indicated small differences compared to the differences between the children with cerebral palsy and those with able bodies (fig 5). DISCUSSION The purpose of this investigation was to develop a method to quantify the degree of spasticity that would be useful in the clinical setting. Priorities for this method included equipment that was available to many centers, ease of operation, applicability to a variety of joints and muscles, and simple but meaningful results. To maintain both clinical and mechanical relevance and to maximize simplicity of results, spasticity was characterized as a velocity-dependent resistance to passive stretch. 5-7 A number of limitations are associated with this investigation. The tests for spasticity measure the resultant torque about the knee joint. This resultant joint torque is the sum of all the
...'"
0 ...-"
-2, ..,'""
o
E-
-4-
o
,.."* -6-
ml
-6-
[ K ~ -10 -70 -60
_T~Kn~eeExtended I ~ -50
-40 -30 -20 -10 0 KinComAngle(degrees)
10
20
,,g/-~ 30
Fig 3. Results of the passive resistance tests for a typical child with spastic diplegic cerebral palsy (girl, age 12 years, mass 39kg}. In contrast to the results presented in figure 2, this test showed an increase in resistance corresponding to an increase in speed of knee extension, reflecting the velocity-dependent resistance to stretch characteristic of children with cerebral palsy. Inertial and gravitational effects have been accounted for in the torque values.
Arch Phys Med Rehabil Vol 77, June 1996
2
0
1'0
2'0
~o
4o
10
~0
#0
do
$0
lO0
Velocity of Knee Extension(degrees/s) Fig 4. Work done by the KinCom machine on the children with cerebral palsy and on the children with able bodies presented in table 1 and plotted as a function of velocity. Linear regression lines are included with their slopes. The slope for the children with cerebral palsy was approximately 10 times greater than the corresponding slope for the children with able bodies. The slopes were significantly different (Cerebral palsy slope [---] - .033; able body slope [ - - | = .0031),
SPASTICITY MEASURE IN CHILDREN WITH CP, Engsberg
0.03 "~ 0.02 CD 0.01 ..~
A A
0.00
A
r~
-0.01
Patients Fig5. Preliminary test-retest results for two children with cerebral palsy. One child was tested at 34 and 41 weeks after surgery and a second child was tested at 10 and 21 months after surgery. The difference between the repeat testing was far smaller than the differences between the averages for the children with cerebral palsy and those with able bodies ([], children with able bodies; A, children with cerebral palsy; A SDR posttests at 7-week interval; A, SDR posttests at 14-week interval).
individual torques that can occur about a joint (eg, agonist and antagonistic muscles). The present investigation did not determine these individual contributions to the resultant joint torque. This limits to some degree the interpretation of the results if, for example, during the spasticity tests for the hamstrings there was torque generated by the quadriceps. This quadriceps torque would assist the machine in its movement to full extension and produce a resultant joint torque that would underestimate the hamstring passive resistive torque. The extensor torque with the knee in a flexed position at the start of the tests for the children with cerebral palsy (fig 3) was probably related to the passive muscle elements of the quadriceps. The collection of EMG data from the muscles crossing the knee would have aided in the understanding of this condition, although it would not have permitted any additional quantification of torque because the relationship between EMG and torque is difficult to determine. Regardless, EMG equipment was not available while this investigation was being conducted. The estimation of the mass of the leg and foot due to gravity was 5.8% of total body massJ 4 This calculation was based on measurements taken from adults and it should be noted that children may have a slightly different percentage. It should also be noted that this estimation does not affect the results of the measure for spasticity because a change in mass estimation of the leg and foot would only shift the torque-angle curves (eg, figs 2 and 3) up or down. Since this shift would be the same for all speeds, it would alter the work done by the KinCom on the child by proportional amounts, thus producing the same slope (ie, our measure for spasticity). A more accurate estimate of the mass of the leg and foot would become critical if the data from figures 2 and 3 were used in another manner. For example, if the average of the four work values was to be used as an estimate of spastic hypertonia, then a vertical shift in the curves would become important. A shift up or down would increase or decrease the value of this measure. The KinCom angles presented in figures 2 and 3 quantify the angular orientation of the KinCom lever arm and not the knee joint angle of the child. An offset between the lever arm and the leg existed. A lever arm-leg angular relationship was not essential to the investigation and, therefore, not determined for all children. However, the offset has been estimated to be between 10° and 15°.
597
The present investigation focuses solely on knee joint extension. The KinCom is capable of performing the same functions at many other joints of the body besides the knee (eg, ankle, elbow, hip). It is thus a relatively straightforward process to adapt the methods presented here to other joints. Spasticity has been characterized by muscle hypertonia, ~2 hyperactive deep tendon reflexes,3 clonus,4 and velocity-dependent resistance to passive stretch. 5-7The characterization chosen for this investigation was velocity-dependent resistance to passive stretch. It was chosen because it was not only clinically relevant but also contained three elements that were fundamental to mechanical engineering principals. These key elements were stretch, resistance, and velocity. The stretch was related to an angular joint range of motion, the resistance to the torque about the joint, and the velocity to the rate of angular change of the joint. Further, the torque and angular range of motion values could be combined into the common mechanical term, work (ie, fT*d0). The simple statistical technique of linear regression permitted the creation of the single variable, slope, for quantifying spasticity. The ability to relate the variables to fundamental mechanical and statistical principals was very important because the validity of the measure was impossible to assess. No "gold standard" exists from which to make a comparison.22Therefore it was reasoned that the measure would be valid if it quantified the key elements of its characterization. The Modified Ashworth scale is the only measure for spasticity that is presently being used in a clinical settingJ ~ The scale permits a rapid assessment of many joints, but it does not directly assess any velocity component associated with spasticity, it only records ordinal data, and its reliability has been questionedJ ~ Like the measure presented in the current investigation its validity cannot be compared to a "gold standard."2z It also cannot be considered as a "gold standard." Nevertheless, the Modified Ashworth scale was used to assess some of the children recruited for this investigation (n = 12). A correlation between it and the measure of the present investigation was quite low (r = .28). Further review indicated that the Ashworth assessments were made by five different physical therapists. No interrater reliability was appraised. It has been reported that the mean interrater correlation between three practitioners assessing the degree of spasticity at the knee was .45. ~ It was concluded that additional work was required to make a more realistic comparison between the two measures. Reliability of the measurement is a key factor in determining its utility. A thorough assessment of the reliability of the measure presented in this investigation has not yet been completed. The majority of the children tested were seen the day before their selective dorsal rhizotomy surgery. This preoperation day was filled with numerous other commitments related to the surgery, thus preventing the children from being accessible for repeat testing. Further, most of the children were not from the surrounding area and could not be expected to bear the expense of arriving a day early for repeat testing. It was fortunate, however, that one child had to retm'n to the hospital 7 weeks after his 8-month postoperative visit and a second child could be retested at his 2-year follow-up visit. The length of time between repeat testing and the small differences compared with the difference between the children with cerebral palsy and those with able bodies are encouraging results for good reliability of the measure. Additional work is required to confirm or refute these preliminary results. It is important to note that the present investigation did not attempt to separate the resistive torque into that attributed to the active and passive components of muscleJ 4 This is a limitation of the investigation because such information would be quite valuable. However, such a separation was not part of
Arch Phys Med Rehabil Vol 77, June 1996
598
SPASTICITY MEASURE IN CHILDREN WITH CP, Engsberg
the clinical characterization of spasticity that was used in the investigation. A "velocity-dependent resistance to stretch" does not differentiate between active and passive components. Previous investigators have conducted tests similar to the ones carried out in the present investigation.9'~8'~9For example, torque-angle curves at 30°, 60 °, and 120°/sec for knee extension were obtained from patients with paraparesisJ 8 The shapes of the curves and peak torques were presented and were similar to the results displayed in figures 2 and 3. However, no investigators have processed the torque-angle-velocity data to produce a single mechanically based variable to simultaneously quantify the three components characterizing spasticity--speed, resistance, and range of motion. It should be noted that previous investigators have employed a slope of a regression line as a means of assessing spasticity.~9'z3 Otis and colleagues x9measured resistance to motion of the plantarflexor muscles during a passive dorsiflexion motion in spastic and normal patients at four different speeds. Linear regression was used to determine the slopes of two torque values at 0° and 15° of plantarflexion over the four speeds. Significant differences were found between the two groups of patients. However, these investigators only considered torque values at two angular positions and not over the full range of motion. Another group of investigators determined a slope from a sum of peak torque values plotted against velocity.22 These resistive peak torque values were influenced by the acceleration phase of the movement. Thus, in addition to possibly containing a resistive component due to spasticity, the torques were also related to (1) acceleration, (2) length of time the limb was accelerated, and (3) mass and moment of inertia of the limb. The report did not explain how these latter values influenced the torques. Finally, while incorporating a torque and velocity component to their measure, the range of motion was not directly included. Our investigation incorporated the torque over the entire range of motion by calculating the work done by the machine on the child. When this work was plotted against velocity and the slope was determined, it simultaneously integrated the three key elements characterizing spasticity for this investigation. Previous investigators attempting to determine a measure to quantify spasticity using dynamometers over a larger range of motion have examined peak resistive torques at the elbow. ~ It was concluded that the peak torques were relatively insensitive to velocity. An eightfold increase in velocity evoked at most a 20% to 30% increase in peak torque. Similarly, Otis J9 indicated a measure that may also have lacked sensitivity. For a tenfold increase in velocity they observed a threefold increase in slope value. Our preliminary work examining only peak torques led to a similar conclusion as the previous two investigations. However, when we simultaneously integrated both the torque and the range of motion into a work variable and plotted it against velocity, we obtained a more sensitive measure. For the children with cerebral palsy, a ninefold increase in velocity produced approximately a tenfold increase in slope. An important factor in the development of this measure was its clinical utility. Clinical utility included the use of equipment that was available to many centers and easy to operate, short data collection and processing times, and results that would be simple but meaningful. Most of the objective measures used to quantify spasticity require custom-made equipment that is not available to all hospitals and clinicsJ "3'4"~2-~4't7'~9 The present investigation used a KinCom dynamometer. This machine and ones like it can be purchased and located in the hospital or clinic setting. The KinCom for the present investigation was located in the gymnasium of the physical therapy department of the hospital. Two physical therapists with no prior training on the machine collected all of the data. After a few hours of
Arch Phys Med Rehabil Vol 77, June 1996
training and practice with volunteers, the therapists could quite adequately operate the equipment. Previous investigations do not mention the amount of time required to collect and process the data. Our investigation required about 30 minutes to collect the data on the patients. Presently, the processing of the data is performed in a spreadsheet package and takes about 90 minutes. However, it would be possible to reduce this processing time with the development of custom software. Nevertheless, it is presently possible to have output available to clinicians after about 2 hours. In the setting in which the method proposed in this investigation would be used, 2 hours is not an inconvenience to the clinician, child, or parents. Finally, many of the objective measures used to quantify spasticity are not always easy to understand and are difficult to interpret, f'9'r2-t4'lT'18For example, a dynamic index determined from EMG measurements indicated significant differences between normal and spastic patients. ~2This index was determined by bandpass filtering the raw EMG signal, full-wave rectification with low-pass filter, normalization and ensemble averaging, integration of area under the curve, and division of specifically defined " o n " areas by "off" areas. The elaborate processing, difficulties in relating EMG to force, and lack of clear understanding of the result make this measure difficult to understand and interpret and inconvenient to use in a clinical setting. Other measures such as complex diagrams, pathlengths, and sums have been reported as single objective variables for spasticity.14'23"24These measures are certainly valuable to the understanding and characterization of spasticity; however the complexity associated with their development, understanding, and interpretation may make them difficult for clinicians to understand and interpret. The measure for spasticity used in the present investigation is also a single number. It is based on elementary mechanical (ie, torque, displacement, work) and statistical (ie, linear regression) principals. Clinicians, technicians, nurses, and therapists are all exposed to these principals during their basic educational training.
Acknowledgment: The authors thank the St. Louis Children's Hospital for supporting this work and the Department of Therapy Services for permitting the use of their KinCom. References 1. Rymer WZ, Powers RK. Pathophysiology of muscular hypertonia in spasticity. In: Park TS, Phillips LH, Peacock WJ, editors. Neurosurgery: state of the art reviews. Philadelphia: Hanley & Belfus, 1989;4:291-301. 2. KatzRT, Rymer WZ. Stastic hypertonia: mechanismsand measurement. Arch Phys Med Rehabil 1989;70:144-55. 3. Miglietta OE, Lowenthal M. Measurement of the stretch reflex response as an approach to the objective evaluation of a spasticity. Arch Phys Med Rehabil 1962;43:62-8. 4. Skinner SR. Direct measurement of spasticity. In Sussman MD, editor. The diplegic child. Rosemont (IL): American Academy of Orthopaedic Surgeons, 1992:31-44. 5. Dimitrijevic MR. Spasticity. In: Swash M, Kennard C, editors. Scientific basis of clinical neurology. Edinburgh: Churchill Livingstone, 1985. 6. Jones EW, Mulley GP. Tlie measurement of spasticity. In: Rose FC, editor. Advances in stroke therapy. New York: Raven Press, 1982:187-95. 7. Lance JW. Symposium synopsis. In: Feldman RG, Young RR, Koella WP, editors. Spasticity: disordered motor control. Chicago: Year Book Medical Publishers, 1980:485-94. 8. Bobath B. Treatment principles and planning in cerebral palsy. Physiotherapy 1963;Aug:l-3. 9. Dahlin M, Knutsson E, Nergardh A. Treatment of spasticity in children with low dose benzodiazepine.J Neurol Sci 1993;117:5460.
SPASTICITY MEASURE IN CHILDREN WITH CP, Engsberg
10. Park TS, Gaffney PE, Kaufman BA, Molleston MC. Selective lumbosacral dorsal rhizotomy immediately caudal to the conus medullaris for cerebral palsy spasticity. Neurosurgery 1993;33:929-34. 11. Bohannon RW, Smith MB. Interrater reliability of a modified Ashworth scale of muscle spasticity. Phys Ther 1987;67:206-7. 12. Fung J, Barheau H. A dynamicEMG profile index to quantify muscular activation disorder in spastic paretic gait. Electroencephalogr Clin Neurophysiol 1989;73:233-44. 13. Simons DG, Sweetser TH. Effects of hemiparesis and handgrip on the mean response and variability of the knee-jerk. Am J Phys Med 1973; 52:221-42. 14. Lehmann JF, Price R, deLateur B J, Hinderer S, Traynor C. Spasticity: quantitative measurements as a basis for assessing effectiveness of therapeutic intervention. Arch Phys Med Rehabil 1989; 70:615. 15. Sloan RL, Sinclair E, Thompson J, Taylor S, Pentland B. Interrater reliability of the modified ashworth scale for spasticity in hemiplegic patients. Int J Rehabil Res 1992; 15:158-61. 16. Cahan LD, Adams JM, Perry J, Beeler LM. Instrumented gait analysis after selective dorsal rhizotomy. Dev Med Child Neurol 1990; 32:1037-43. 17. Stam J and Tan KM. Tendon reflex variability and method of stimulation. Electroencephalogr Clin Neurophysiol 1987; 67:463-7.
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18. Knutsson E. Quantification of spasticity. In: Struppler A, Weindl A. Electromyography and evoked potentials. Berlin: Springer-Verlag, 1985:84-91. 19. Otis JC, Root L, Pamilla JR, Kroll MA. Biomechanical measurement of spastic plantarflexors. Dev Med Child Neurol 1983; 25:606. 20. Clauser CE, McConville JT, Young JW. Weight, volume, and center of mass of segments of the human body. No.: AMRL-TR-69-70. Wright-Patterson Air Force Base, OH, 1969. 21. Kuo BC. Automatic control systems. Englewood Cliffs, NJ: Prentice-Hall Inc., 1987:313-26. 22. DavidoffRA. Antispasticity drugs: mechanisms of action. Ann Neurol 1985; 17:107-16. 23. Firoozbakhsh KK, Kunkel CF, Scremin AM, Moneim MS. Isoldnetic dynamometric technique for spasticity assessment. Am J Phys Med Rehabil 1993;72:379-85. 24. Price R, Bjomson KF, Lehmann JF, McLaughlin JF, Hays RM. Quantitative measurement of spasticity in children with cerebral palsy. Dev Med Child Neurol 1991;33:585-95.
Supplier a. Chattanooga Group, Inc., 4717 Adams Road, PO Box 489, Hixson, TX 37343-0489.
Arch Phys Med Rehabil Vol 77, June 1996
Quantitative Clinical Measure of Spasticity in Children With Cerebral Palsy Jack R. Engsberg, Phi), Kenneth S. Olree, MS, Sandy A. Ross, MHSPT, T. S. Park, MD ABSTRACT. Engsberg JR, Olree KS, Ross SA, Park TS. Quantitative clinical measure of spasticity in children with cerebral palsy. Arch Phys Med Rehabil 1996;77:594-9.
Objective: This investigation developed an objective measure to quantify the degree of spasticity. Design: Specifications included a single variable that integrated key elements characterizing spasticity: velocity, range of motion, and resistance to passive motion. A dynamometer at a children's hospital quantified the passive resistance of the hamstrings to knee extension for a range of motion at 4 different speeds for the prospective descriptive investigation. Patients: A convenience sample of six children with able bodies and 17 children with spastic diplegic cerebral palsy volunteered. Data Processing: Torque-angle data were processed to calculate the work done by the machine on the children for each speed and then determine the slope of the work-velocity curves. This slope was considered to be the measure of spasticity and it was hypothesized that children with cerebral palsy would have a greater slope than children with able bodies. An independent t test determined whether a significant difference existed between groups (p < .05). Results: Torque-angle data for children with able bodies indicated little change in passive resistance as a function of speed. Similar data for children with cerebral palsy indicated larger resistive torques with increasing speed. Slope from the workvelocity data was close to zero for children with able bodies [.003 J/(°/sec)], while the corresponding slope for children with cerebral palsy was approximately 10 times greater [.031 J/(°/ sec)] and significantly different (p < .05). Conclusion: The slope of the work-velocity data integrates three major components characterizing spasticity, it is a single number that can easily be evaluated and interpreted in a clinical setting, and it utilizes a machine that is available at many centers. © 1996 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation MAJOR IMPAIRMENT in cerebral palsy is spasticity. Clinically, the term spasticity is often used to refer to a number of impairments, including muscle hypertonia, ~'2 hyperactive deep tendon reflex,3 clonus, 4 and velocity-dependent resistance to passive stretch. 5-7 Many surgical and therapeutic procedures are performed, and many pharmacological drugs are
A
From the Motion Analysis Laboratory, Department of Neurosurgery, St. Louis Children's Hospital (Dr. Engsberg, Mr. Olree, Ms. Ross, Dr. Park) and Washington University School of Medicine (Dr. Engsberg, Dr. Park), St. Louis, MO. Submitted for publication June 27, 1995. Accepted in revised form December 14, 1995. No commercial party having a direct or indirect interest in the subject matter of this article has or will confer a benefit upon the authors or upon any organization with which the authors are associated. Reprint requests to Jack R. Engsberg, PhD, Director, Motion Analysis Laboratory, St. Louis Children's Hospital, One Children's Place, St. Louis, MO 63110. © 1996 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation 0003-9993/96/7706-357453.00/0
Arch Phys Med Rehabil Vol 77, June 1996
administered to children with cerebral palsy to minimize or eliminate the influence of spasticity.8-m Methods to quantify the various types of spasticity include the Modified Ashworth scale, electromyography (EMG), deep tendon reflex tests, and resistance-to-motion t e s t s . I-4'9'tH4 Of these four methods for assessing spasticity only the Modified Ashworth scale is regularly used in a clinical setting] ~ The Modified Ashworth Scale involves manually moving a limb through the range of motion to passively stretch specific muscle groups. The scale permits a rapid assessment of the degree of spasticity about many joints. However, although its use is widespread in clinical and research settings for assessing spasticity, it remains a basically subjective measure recorded in ordinal data.l ~ As a consequence, its reliability has been called into question. 15 In contrast to the Modified Ashworth scale, the remaining three methods for assessing the degree of spasticity are objective measures. These tests, however, have limitations that prevent them for being used regularly in a clinical setting. EMG has been used to examine muscle activity in spastic adults and children undergoing selective dorsal rhizotomy surgery] 2A6Although it provides insight into the activity of the muscle, the methods are difficult to use clinically. The EMG signal is highly dependent on the techniques used to record them (eg, electrode type, electrode placement) and on the muscle under examination? Further, the relationship between EMG and muscle force is not easily quantified. Deep tendon reflex tests apply an impact load to a specific tendon and measure EMG, leg displacements, force, or acceleral i o n s . 4'13'17 Custom-made devices have been developed to standardize the impact to the tendon] 7 Nevertheless, these devices may not be applicable to other tendons, and the generalization of results to other joints is unknown. Resistance-to-motion tests seem to fail into two types. Both types assess resistance to motion with dynamometers; one type measures the resistance during small oscillations and the other measures resistance over a large range of m o t i o n . 9'14']839 In both cases the tests are not regularly used in a clinical setting. Some of these tests require custom-made equipment not available to many centers. 14'~9Some do not provide information that can be easily understood and interpreted by the clinician. TM Often the device is not applicable to a variety of joints or muscles, t'4'w The purpose of this investigation was to develop a method to quantify the degree of spasticity that would be useful in the clinical setting. Priorities for this method included equipment that was available to many centers, ease of operation, applicability to a variety of joints and muscles, and simple but meaningful results. To maintain both clinical and mechanical relevance, and to maximize simplicity of results, spasticity was characterized as a velocity-dependent resistance to passive stretch. 5-7
METHODS For this prospective, descriptive investigation, a convenience sample of six children with able bodies (mean age 9 years, range 4 to 17; 2 boys, 4 girls; mean mass 34.5kg, SD 17.9) and 17 children with spastic diplegie cerebral palsy (mean age 10 years, range 4 to 16; 8 boys, 9 girls; mean mass 32.3kg, SD 14.6) were tested. The children with able bodies were recruited
SPASTICITY MEASURE IN CHILDREN WITH CP, Engsberg
through parents within the hospital community or were siblings of children visiting the hospital. The children with cerebral palsy had been referred to the motion analysis laboratory for other testing by an orthopedic surgeon or were scheduled to undergo a selective dorsal rhizotomy the following day and were referred to the laboratory by a neurosurgeon. The clinical diagnosis of spastic diplegic cerebral palsy was made by the referring physician. Only children who were large enough to fit comfortably on the test equipment and who would presumably cooperate were approached for participation. All parents and children who were asked to participate consented. Each child and/or parent was informed about the project and gave informed consent. In each child with an able body only one leg was tested. Attempts were made to test both legs of the children with cerebral palsy, but if a child became tired, bored, or uncooperative, only one leg was tested. Initial efforts at determining the reliability of the measure were accomplished by testing two children at two different times after their selective dorsal rhizotomy surgery. One child was tested at 34 and 41 weeks after surgery and a second child was tested at 10 and 21 months after surgery. The KinCom dynamometer~can move the passive leg through a range of motion at a specified speed, measuring the force applied to a support arm during the motion. Each child sat on the KinCom with stabilization straps across the distal aspect of the thigh and pelvis. The child was supported at his or her back and was capable of maintaining an upright position. The axis of the KinCom was aligned with the knee axis of the child. The leg of the child was attached to the support arm by securing the leg against a tibia pad with Velcro straps. A fixed laboratory coordinate system was established by moving the lever arm to a horizontal position (0°). Torques were calculated by inputting the distance of the tibia pad from the rotation axis of the machine. Before conducting the spasticity tests, the anatomic range of motion limits for knee extension or hamstring length were established for each child. The starting position for the test was approximately 60 ° below the horizontal, although this position was decreased to 50 ° if substantial quadriceps resistance existed. A special feature of the KinCom was used to determine the limits for knee extension. This feature caused the machine to stop if a preset force (ie, termination force) was reached. Initially, the machine was set to take the knee of the child beyond its physiological limits. To prevent this from happening a low termination force value was programmed into the machine to stop the test. The end range of extension motion was determined by assigning a speed of 10°/sec to the KinCom and engaging the passive mode. The child was instructed not to help the lever arm move and remain as relaxed as possible as the leg rotated from a flexed to an extended position. The end range of motion for knee extension was determined and recorded by gradually increasing the termination force until the child felt uncomfortable, the pelvis began to rotate posteriorly, or the knee began to rise. The final termination force values were converted to torques for each child and ranged between 6 and 20Nm. To insure the safety of the child an adult closely observed the tests and held a button that, if pressed, would stop the test. The spasticity tests were then conducted. These tests were similar to the previous one except that the end range of extension motion was used to stop the tests instead of a termination force value. The starting angle remained at approximately 60 ° below the horizontal. The termination force was increased from its preset value to assure that the end range of motion was achieved. Tests for knee extension were conducted at speeds of 10°, 30°, 60 °, and 90°/sec, and the resistive torque was continuously monitored during the trials.
0-
595
..........
" ................
_2J v
-6"
-8"
Knee Flexed ] -lC -7o -~o -~o
4o
-5o -~o -10 KinCem Angle (degrees)
IKnee Extended 1'o ~o 30
Fig 1. Quantification of the work done (torque × angular displacement) by the KinCom machine on one subject at one speed (shaded area). The boundaries for the a r e a were the torque-angle curve, the zero torque line, and the end range of motion (about 12°). A work value was calculated for each of the four speeds for each child. Inertial and gravitational effects have been accounted for in the torque values.
The force data from each child were downloaded to a personal computer in which the weight of the leg and foot due to gravity, estimated to be 5.8% of total body weight, was partialled out in a custom computer program. 2° The acceleration of the leg from a motionless position to a constant angular velocity produced a torque component in the data that was unwanted. As would be expected this component was increased as both the speed of the test and the mass of the leg and foot increased. These inertial effects were removed by modeling the acceleration component as an underdamped second-order system and subtracting it from the torque values.2~ The areas quantifying the work done (ie, fT*d0 where T = Torque and dO is a small angular displacement measured in radians) by the machine on the child were calculated using the trapezoid rule. The boundaries for the areas were the torqueangle curve, the zero torque line, and the end range of motion (fig 1). Four areas quantifying work were determined for each child for the given speeds (ie, 10°, 30°, 60 °, 90°/sec). Linear regression was used to determine the line of best fit for these four areas as a function of speed. The slope of the linear regression line was considered to be the measure of spasticity. It was hypothesized that the children with able bodies would have slopes close to zero because they have no velocity-dependent resistance to stretch and the children with cerebral palsy would have slopes greater than zero because they do have a velocitydependent resistance to stretch. Because not all children wit~l cerebral palsy had both legs tested, the single leg tested was used in the analysis (n = 6). In the cases where both legs were tested, a single leg from each child was randomly chosen for analysis (n = 11). A chi-squared test was performed to determine if the distribution of the slopes for the children with cerebral palsy were significantly different from a normal distribution. Since no significant difference was found (p < .01) an independent t test was used to determine if a significant difference existed between the slopes for the two groups of children (p < .05). RESULTS Torque-angle data for a typical child with an able body indicated very little change in resistive torque as a function of speed
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596
SPASTICITY MEASURE IN CHILDREN WITH CP, Engsberg Table 1: Work Done by the KinCom Machine on Childrens' Knees
2
Work (Joules) 0
Subjects
10°/sec
30°/sec
60°/see
90°/sec
-2-
Able body (n = 6) SD Cerebral palsy (n = 17) SD
2.81 2.48 2.81 1.92
2.78 2.35 3.82 2.40
2.91 2.12 4.22 2,30
3.04 2.11 5.52 3.04
E z -4
Means and standard deviations for the work done (ie, torque x angular displacement) by the KinCom machine on knees of the children with cerebral palsy and the children with able bodies at 4 speeds of knee extension in the upright position. The work remained relatively constant regardless of the speed for the children with able bodies. In contrast, the work for the children with cerebral palsy increased as thespeed increased.
O F--8"
I to dens
-8"
Knee Flexed } -10 -70-60 -50
[ Knee Extended -40 -30 -20 -10 KinCorn Angle (degrees)
1'0
20
30
Fig 2, Results of the passive resistance tests for a typical child with an able body (girl, age 7 years, mass 26kg). Very little difference existed between curves regardless of the speed of knee extension, indicating little relationship between resistance and speed through the range of motion. Inertial and gravitational effects have been accounted for in the torque values.
because all curves were essentially the same (fig 2). In addition, the ordering of the curves according to magnitude did not progressively increase or decrease. In contrast, similar data for a typical child with cerebral palsy indicated larger resistive torques with an increase in speed (fig 3). An extensor torque (ie, positive value) existed for about the first 20° to 25 ° of motion for both groups of children, The presence of the extensor torque before a flexor torque was common in most children. The work done (fig 1) by the machine on the knees of the children with able bodies remained relatively constant for the four speeds, whereas the work done on the children with cerebral palsy increased as the velocity increased (table 1). There was an 8% increase from the slow speed to the fast speed in the children with able bodies and a 96% increase from slow to fast for the children with cerebral palsy. The standard deviations were relatively large for both groups of children. This was because of the variability in both the point at which the curves
crossed the 0 torque line and the magnitude of the resistive torque throughout the range of motion. The slope (Joules/(°/sec)) of the linear regression line for work values as a function of velocity (table 1) for the children with able bodies was very close to zero (.0031, SD = .009), whereas the corresponding slope for the children with cerebral palsy was approximately 10 times greater (.033, SD = .019) (fig 4). These slopes were significantly different (p < .05). The repeat testing of the two groups of children after selective dorsal rhizotomy surgery indicated small differences compared to the differences between the children with cerebral palsy and those with able bodies (fig 5). DISCUSSION The purpose of this investigation was to develop a method to quantify the degree of spasticity that would be useful in the clinical setting. Priorities for this method included equipment that was available to many centers, ease of operation, applicability to a variety of joints and muscles, and simple but meaningful results. To maintain both clinical and mechanical relevance and to maximize simplicity of results, spasticity was characterized as a velocity-dependent resistance to passive stretch. 5-7 A number of limitations are associated with this investigation. The tests for spasticity measure the resultant torque about the knee joint. This resultant joint torque is the sum of all the
...'"
0 ...-"
-2, ..,'""
o
E-
-4-
o
,.."* -6-
ml
-6-
[ K ~ -10 -70 -60
_T~Kn~eeExtended I ~ -50
-40 -30 -20 -10 0 KinComAngle(degrees)
10
20
,,g/-~ 30
Fig 3. Results of the passive resistance tests for a typical child with spastic diplegic cerebral palsy (girl, age 12 years, mass 39kg}. In contrast to the results presented in figure 2, this test showed an increase in resistance corresponding to an increase in speed of knee extension, reflecting the velocity-dependent resistance to stretch characteristic of children with cerebral palsy. Inertial and gravitational effects have been accounted for in the torque values.
Arch Phys Med Rehabil Vol 77, June 1996
2
0
1'0
2'0
~o
4o
10
~0
#0
do
$0
lO0
Velocity of Knee Extension(degrees/s) Fig 4. Work done by the KinCom machine on the children with cerebral palsy and on the children with able bodies presented in table 1 and plotted as a function of velocity. Linear regression lines are included with their slopes. The slope for the children with cerebral palsy was approximately 10 times greater than the corresponding slope for the children with able bodies. The slopes were significantly different (Cerebral palsy slope [---] - .033; able body slope [ - - | = .0031),
SPASTICITY MEASURE IN CHILDREN WITH CP, Engsberg
0.03 "~ 0.02 CD 0.01 ..~
A A
0.00
A
r~
-0.01
Patients Fig5. Preliminary test-retest results for two children with cerebral palsy. One child was tested at 34 and 41 weeks after surgery and a second child was tested at 10 and 21 months after surgery. The difference between the repeat testing was far smaller than the differences between the averages for the children with cerebral palsy and those with able bodies ([], children with able bodies; A, children with cerebral palsy; A SDR posttests at 7-week interval; A, SDR posttests at 14-week interval).
individual torques that can occur about a joint (eg, agonist and antagonistic muscles). The present investigation did not determine these individual contributions to the resultant joint torque. This limits to some degree the interpretation of the results if, for example, during the spasticity tests for the hamstrings there was torque generated by the quadriceps. This quadriceps torque would assist the machine in its movement to full extension and produce a resultant joint torque that would underestimate the hamstring passive resistive torque. The extensor torque with the knee in a flexed position at the start of the tests for the children with cerebral palsy (fig 3) was probably related to the passive muscle elements of the quadriceps. The collection of EMG data from the muscles crossing the knee would have aided in the understanding of this condition, although it would not have permitted any additional quantification of torque because the relationship between EMG and torque is difficult to determine. Regardless, EMG equipment was not available while this investigation was being conducted. The estimation of the mass of the leg and foot due to gravity was 5.8% of total body massJ 4 This calculation was based on measurements taken from adults and it should be noted that children may have a slightly different percentage. It should also be noted that this estimation does not affect the results of the measure for spasticity because a change in mass estimation of the leg and foot would only shift the torque-angle curves (eg, figs 2 and 3) up or down. Since this shift would be the same for all speeds, it would alter the work done by the KinCom on the child by proportional amounts, thus producing the same slope (ie, our measure for spasticity). A more accurate estimate of the mass of the leg and foot would become critical if the data from figures 2 and 3 were used in another manner. For example, if the average of the four work values was to be used as an estimate of spastic hypertonia, then a vertical shift in the curves would become important. A shift up or down would increase or decrease the value of this measure. The KinCom angles presented in figures 2 and 3 quantify the angular orientation of the KinCom lever arm and not the knee joint angle of the child. An offset between the lever arm and the leg existed. A lever arm-leg angular relationship was not essential to the investigation and, therefore, not determined for all children. However, the offset has been estimated to be between 10° and 15°.
597
The present investigation focuses solely on knee joint extension. The KinCom is capable of performing the same functions at many other joints of the body besides the knee (eg, ankle, elbow, hip). It is thus a relatively straightforward process to adapt the methods presented here to other joints. Spasticity has been characterized by muscle hypertonia, ~2 hyperactive deep tendon reflexes,3 clonus,4 and velocity-dependent resistance to passive stretch. 5-7The characterization chosen for this investigation was velocity-dependent resistance to passive stretch. It was chosen because it was not only clinically relevant but also contained three elements that were fundamental to mechanical engineering principals. These key elements were stretch, resistance, and velocity. The stretch was related to an angular joint range of motion, the resistance to the torque about the joint, and the velocity to the rate of angular change of the joint. Further, the torque and angular range of motion values could be combined into the common mechanical term, work (ie, fT*d0). The simple statistical technique of linear regression permitted the creation of the single variable, slope, for quantifying spasticity. The ability to relate the variables to fundamental mechanical and statistical principals was very important because the validity of the measure was impossible to assess. No "gold standard" exists from which to make a comparison.22Therefore it was reasoned that the measure would be valid if it quantified the key elements of its characterization. The Modified Ashworth scale is the only measure for spasticity that is presently being used in a clinical settingJ ~ The scale permits a rapid assessment of many joints, but it does not directly assess any velocity component associated with spasticity, it only records ordinal data, and its reliability has been questionedJ ~ Like the measure presented in the current investigation its validity cannot be compared to a "gold standard."2z It also cannot be considered as a "gold standard." Nevertheless, the Modified Ashworth scale was used to assess some of the children recruited for this investigation (n = 12). A correlation between it and the measure of the present investigation was quite low (r = .28). Further review indicated that the Ashworth assessments were made by five different physical therapists. No interrater reliability was appraised. It has been reported that the mean interrater correlation between three practitioners assessing the degree of spasticity at the knee was .45. ~ It was concluded that additional work was required to make a more realistic comparison between the two measures. Reliability of the measurement is a key factor in determining its utility. A thorough assessment of the reliability of the measure presented in this investigation has not yet been completed. The majority of the children tested were seen the day before their selective dorsal rhizotomy surgery. This preoperation day was filled with numerous other commitments related to the surgery, thus preventing the children from being accessible for repeat testing. Further, most of the children were not from the surrounding area and could not be expected to bear the expense of arriving a day early for repeat testing. It was fortunate, however, that one child had to retm'n to the hospital 7 weeks after his 8-month postoperative visit and a second child could be retested at his 2-year follow-up visit. The length of time between repeat testing and the small differences compared with the difference between the children with cerebral palsy and those with able bodies are encouraging results for good reliability of the measure. Additional work is required to confirm or refute these preliminary results. It is important to note that the present investigation did not attempt to separate the resistive torque into that attributed to the active and passive components of muscleJ 4 This is a limitation of the investigation because such information would be quite valuable. However, such a separation was not part of
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598
SPASTICITY MEASURE IN CHILDREN WITH CP, Engsberg
the clinical characterization of spasticity that was used in the investigation. A "velocity-dependent resistance to stretch" does not differentiate between active and passive components. Previous investigators have conducted tests similar to the ones carried out in the present investigation.9'~8'~9For example, torque-angle curves at 30°, 60 °, and 120°/sec for knee extension were obtained from patients with paraparesisJ 8 The shapes of the curves and peak torques were presented and were similar to the results displayed in figures 2 and 3. However, no investigators have processed the torque-angle-velocity data to produce a single mechanically based variable to simultaneously quantify the three components characterizing spasticity--speed, resistance, and range of motion. It should be noted that previous investigators have employed a slope of a regression line as a means of assessing spasticity.~9'z3 Otis and colleagues x9measured resistance to motion of the plantarflexor muscles during a passive dorsiflexion motion in spastic and normal patients at four different speeds. Linear regression was used to determine the slopes of two torque values at 0° and 15° of plantarflexion over the four speeds. Significant differences were found between the two groups of patients. However, these investigators only considered torque values at two angular positions and not over the full range of motion. Another group of investigators determined a slope from a sum of peak torque values plotted against velocity.22 These resistive peak torque values were influenced by the acceleration phase of the movement. Thus, in addition to possibly containing a resistive component due to spasticity, the torques were also related to (1) acceleration, (2) length of time the limb was accelerated, and (3) mass and moment of inertia of the limb. The report did not explain how these latter values influenced the torques. Finally, while incorporating a torque and velocity component to their measure, the range of motion was not directly included. Our investigation incorporated the torque over the entire range of motion by calculating the work done by the machine on the child. When this work was plotted against velocity and the slope was determined, it simultaneously integrated the three key elements characterizing spasticity for this investigation. Previous investigators attempting to determine a measure to quantify spasticity using dynamometers over a larger range of motion have examined peak resistive torques at the elbow. ~ It was concluded that the peak torques were relatively insensitive to velocity. An eightfold increase in velocity evoked at most a 20% to 30% increase in peak torque. Similarly, Otis J9 indicated a measure that may also have lacked sensitivity. For a tenfold increase in velocity they observed a threefold increase in slope value. Our preliminary work examining only peak torques led to a similar conclusion as the previous two investigations. However, when we simultaneously integrated both the torque and the range of motion into a work variable and plotted it against velocity, we obtained a more sensitive measure. For the children with cerebral palsy, a ninefold increase in velocity produced approximately a tenfold increase in slope. An important factor in the development of this measure was its clinical utility. Clinical utility included the use of equipment that was available to many centers and easy to operate, short data collection and processing times, and results that would be simple but meaningful. Most of the objective measures used to quantify spasticity require custom-made equipment that is not available to all hospitals and clinicsJ "3'4"~2-~4't7'~9 The present investigation used a KinCom dynamometer. This machine and ones like it can be purchased and located in the hospital or clinic setting. The KinCom for the present investigation was located in the gymnasium of the physical therapy department of the hospital. Two physical therapists with no prior training on the machine collected all of the data. After a few hours of
Arch Phys Med Rehabil Vol 77, June 1996
training and practice with volunteers, the therapists could quite adequately operate the equipment. Previous investigations do not mention the amount of time required to collect and process the data. Our investigation required about 30 minutes to collect the data on the patients. Presently, the processing of the data is performed in a spreadsheet package and takes about 90 minutes. However, it would be possible to reduce this processing time with the development of custom software. Nevertheless, it is presently possible to have output available to clinicians after about 2 hours. In the setting in which the method proposed in this investigation would be used, 2 hours is not an inconvenience to the clinician, child, or parents. Finally, many of the objective measures used to quantify spasticity are not always easy to understand and are difficult to interpret, f'9'r2-t4'lT'18For example, a dynamic index determined from EMG measurements indicated significant differences between normal and spastic patients. ~2This index was determined by bandpass filtering the raw EMG signal, full-wave rectification with low-pass filter, normalization and ensemble averaging, integration of area under the curve, and division of specifically defined " o n " areas by "off" areas. The elaborate processing, difficulties in relating EMG to force, and lack of clear understanding of the result make this measure difficult to understand and interpret and inconvenient to use in a clinical setting. Other measures such as complex diagrams, pathlengths, and sums have been reported as single objective variables for spasticity.14'23"24These measures are certainly valuable to the understanding and characterization of spasticity; however the complexity associated with their development, understanding, and interpretation may make them difficult for clinicians to understand and interpret. The measure for spasticity used in the present investigation is also a single number. It is based on elementary mechanical (ie, torque, displacement, work) and statistical (ie, linear regression) principals. Clinicians, technicians, nurses, and therapists are all exposed to these principals during their basic educational training.
Acknowledgment: The authors thank the St. Louis Children's Hospital for supporting this work and the Department of Therapy Services for permitting the use of their KinCom. References 1. Rymer WZ, Powers RK. Pathophysiology of muscular hypertonia in spasticity. In: Park TS, Phillips LH, Peacock WJ, editors. Neurosurgery: state of the art reviews. Philadelphia: Hanley & Belfus, 1989;4:291-301. 2. KatzRT, Rymer WZ. Stastic hypertonia: mechanismsand measurement. Arch Phys Med Rehabil 1989;70:144-55. 3. Miglietta OE, Lowenthal M. Measurement of the stretch reflex response as an approach to the objective evaluation of a spasticity. Arch Phys Med Rehabil 1962;43:62-8. 4. Skinner SR. Direct measurement of spasticity. In Sussman MD, editor. The diplegic child. Rosemont (IL): American Academy of Orthopaedic Surgeons, 1992:31-44. 5. Dimitrijevic MR. Spasticity. In: Swash M, Kennard C, editors. Scientific basis of clinical neurology. Edinburgh: Churchill Livingstone, 1985. 6. Jones EW, Mulley GP. Tlie measurement of spasticity. In: Rose FC, editor. Advances in stroke therapy. New York: Raven Press, 1982:187-95. 7. Lance JW. Symposium synopsis. In: Feldman RG, Young RR, Koella WP, editors. Spasticity: disordered motor control. Chicago: Year Book Medical Publishers, 1980:485-94. 8. Bobath B. Treatment principles and planning in cerebral palsy. Physiotherapy 1963;Aug:l-3. 9. Dahlin M, Knutsson E, Nergardh A. Treatment of spasticity in children with low dose benzodiazepine.J Neurol Sci 1993;117:5460.
SPASTICITY MEASURE IN CHILDREN WITH CP, Engsberg
10. Park TS, Gaffney PE, Kaufman BA, Molleston MC. Selective lumbosacral dorsal rhizotomy immediately caudal to the conus medullaris for cerebral palsy spasticity. Neurosurgery 1993;33:929-34. 11. Bohannon RW, Smith MB. Interrater reliability of a modified Ashworth scale of muscle spasticity. Phys Ther 1987;67:206-7. 12. Fung J, Barheau H. A dynamicEMG profile index to quantify muscular activation disorder in spastic paretic gait. Electroencephalogr Clin Neurophysiol 1989;73:233-44. 13. Simons DG, Sweetser TH. Effects of hemiparesis and handgrip on the mean response and variability of the knee-jerk. Am J Phys Med 1973; 52:221-42. 14. Lehmann JF, Price R, deLateur B J, Hinderer S, Traynor C. Spasticity: quantitative measurements as a basis for assessing effectiveness of therapeutic intervention. Arch Phys Med Rehabil 1989; 70:615. 15. Sloan RL, Sinclair E, Thompson J, Taylor S, Pentland B. Interrater reliability of the modified ashworth scale for spasticity in hemiplegic patients. Int J Rehabil Res 1992; 15:158-61. 16. Cahan LD, Adams JM, Perry J, Beeler LM. Instrumented gait analysis after selective dorsal rhizotomy. Dev Med Child Neurol 1990; 32:1037-43. 17. Stam J and Tan KM. Tendon reflex variability and method of stimulation. Electroencephalogr Clin Neurophysiol 1987; 67:463-7.
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18. Knutsson E. Quantification of spasticity. In: Struppler A, Weindl A. Electromyography and evoked potentials. Berlin: Springer-Verlag, 1985:84-91. 19. Otis JC, Root L, Pamilla JR, Kroll MA. Biomechanical measurement of spastic plantarflexors. Dev Med Child Neurol 1983; 25:606. 20. Clauser CE, McConville JT, Young JW. Weight, volume, and center of mass of segments of the human body. No.: AMRL-TR-69-70. Wright-Patterson Air Force Base, OH, 1969. 21. Kuo BC. Automatic control systems. Englewood Cliffs, NJ: Prentice-Hall Inc., 1987:313-26. 22. DavidoffRA. Antispasticity drugs: mechanisms of action. Ann Neurol 1985; 17:107-16. 23. Firoozbakhsh KK, Kunkel CF, Scremin AM, Moneim MS. Isoldnetic dynamometric technique for spasticity assessment. Am J Phys Med Rehabil 1993;72:379-85. 24. Price R, Bjomson KF, Lehmann JF, McLaughlin JF, Hays RM. Quantitative measurement of spasticity in children with cerebral palsy. Dev Med Child Neurol 1991;33:585-95.
Supplier a. Chattanooga Group, Inc., 4717 Adams Road, PO Box 489, Hixson, TX 37343-0489.
Arch Phys Med Rehabil Vol 77, June 1996