Objective: To compare pendulum test data obtained using an electrogoniometer ... of Toronto. (.Ms. Jamshidi). and the A. T. Jousae Research Lahoralory. I.yndhurst. .... Char? to be sufficient to allow for sufficient recovery of the reflex pathways ...
1129
Clinical Measurement of Spasticity Using the Pendulum Test: Comparison of Electrogoniometric and Videotape Analyses Maryam Jamshidi,
BSc, PT, Andrew W. Smith, PhD
ABSTRACT. Jamshidi M, Smith AW. Clinical measurement of spasticity using the pendulum test: comparison of electrogoniometric and videotape analyses. Arch Phys Med Rehabil 1996: 77: I 129-32.
Objective: To compare pendulum test data obtained using an electrogoniometer with data obtained by videotape. The issue of video digitization error was also addressed. Design: The study compared pendulum test relaxation indices determined from data simultaneously collected using (1) a video (VID) camera and (2) an electrogonimeter (EG). Setting: A spinal cord injury rehabilitation center. Subjects: Three persons with a spinal cord injury (SCI) exhibiting mild, moderate, and severe spasticity, respectively, and a fourth, non-SC1 subject. Main Outcome Measure: Relaxation index as a descriptor of lower limb muscle spasticity measured using the pendulum test. Results: Multiple-digitization of VID data did not affect the reliability of this technique. It was noted that reflective markers located on body landmarks resulted in more reliable data as opposed to markers placed on the EG. Both EC and VID data were accurate and reliable. Conclusions: In the VID method, using one digitization by a single operator is sufficient. The appropriate placement of light reflector markers are on body points. EC and VID are both reliable, highly correlated. and interchangeable in measuring spasticity using the pendulum test. 0 1996 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehahilitution
T
HE PENDULUM TEST’,’ of spasticity is assessed by means of the calculation of a ratio of knee angles measured during the swinging of the lower leg in a pendulum-like movement. This test has been applied using several measurement devices, including goniometers,*-’ videotaped recordings,h and isokinetic dynamometers.7 Goodwin et al’ compared the reliability and intcrchangeability of three types of goniometers, including a universal goniometer. fluid goniometer, and electrogoniometer. They reported that the use of the electrogoniometer reduced the variability From the Graduate Department of Community Health. Uni\ersiry of Toronto (.Ms. Jamshidi). and the A. T. Jousae Research Lahoralory. I.yndhurst. The Spmal Cord Centre (Dr. Smith). Toronto. Onkwio. Canada. Suhmirred for publication November 14. lYY.5. Accepted in revised form April Il. lY96. Supponed by the Lyndhurrt Hospital Foundation and the A. T. Joursr Lahorawry Endowment Fund. No commercial party having 3 direct linoncial inrerest in the results of the rrwarch supporting this article has or will confer a benefit upon the aulhors or upon any organizuion wilh which the authors are awxiared. Reprint requests to Andrew W. Smith. PhD. A. T. Jourse Research Laboratory. Lyndhursr. The Spinal Cord Cenk. 20 Sutherland Drive. Toronto. Onrario M4G 3’49 Canada. 0 1990 by the American Congrcaa of Rehabilitation Medicine and the Anwican Academy of Physical Medicine and Rehahilhation 0003-9993/96177 I I -3765S3.00/0
between testers. Also, they noted that the different types of goniometers should not be used interchangeably. Stillman et al’ performed the pendulum test using a procedure involving computerized video motion analysis for purposes of investigating reliable and valid indicators of the damped, unsustained, oscillatory motion that characterizes this test. Their results were congruous with those obtained by other studies using the goniometric version of the test. They also concluded that the video-based pendulum test is a simple, reliable source of measures with considerable potential for the clinical and physiological investigation of neurological and nonneurological features of normal and abnormal passive joint motion. Bohannon’ studied the reliability of pendulum test using a Cybex II isokinetic dynamometer. It was found that test variability was not significant and correlation between trials was high, and the results suggested broader application of this test to measure spasticity in patients with intracranial lesions. At the time of the present study, the pendulum test is conducted at Lyndhurst Hospital using digitized videotaped data of the subject. The measurement of knee angles and the subsequent assessment of spasticity requires an investment in time and equipment for video digitization. An electrogoniometer, used in conjunction with a microcomputer, is an alternative to videotape in that it allows for almost instantaneous measurement and assessment of spasticity via the pendulum test. The purpose of the present study was to compare pendulum test data obtained using an electrogoniomcter (EG) to that of videotaped (VID) data. To do this, it was necessary to (1) examine the reliability of the EG during the pendulum test, (2) determine the reliability of pendulum test scores resulting from numerous VID digitizations, and (3) investigate the most appropriate placement of light-reflecting markers for the purpose of VID angular displacement measurements.
METHODS Subjects This study included a pilot data collection session involving I normal volunteer and a main study data collection session involving 4 volunteer subjects. Prior to the recruitment of subjects, the study protocol was reviewed and approved by the Ethics Committee of Lyndhurst The Spinal Cord Centre. All subjects read an approved information sheet before entering the study, and informed consent was obtained from all subjects.
Pewhdum Test Protocol The pendulum test was used to determine an index of spasticity, R2n, as outlined by Bajd and Vodovnic.’ This index is a ratio of two ranges of knee angular displacement. Three knee angles are required for the calculation of R2n: the starting angle of the knee (normally full extension), the knee flexion angle on the first swing of the leg (acute angle), and the final resting knee angle. The equation used to determine R2n is as follows: R2n =
(First Acute Angle - Starting Angle) 1.6 x (Resting Angle - Starting Angle)
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where all angles refer to knee flexion/extension angles in the sagittal plane. The pendulum test’ involved the subject lying supine on a plinth such that the posterior aspect of the knee joint was three finger widths beyond the end of the plinth. The subject’s arms were folded across his or her chest throughout the test. The therapist held the heel of the test limb so that the knee was as fully extended as possible without allowing the thigh to leave the plinth. The therapist released the heel and the limb was allowed to oscillate until it came to rest. The test was repeated 10 times in the pilot study and 5 times in the main study with a minimum rest of 30 secondsbetween repetitions. Thirty seconds between pendulum tests has been used in other studies involving the pendulum test,2*3and was considered by Levin and HuiChar? to be sufficient to allow for sufficient recovery of the reflex pathways in their study of spasticity and stretch reflexes. The R2n values of all trials are initially averaged to determine the mean and standard deviation of the test set. Any R2n scores greater than 2 standard deviations from the mean are then excluded and the remaining tests are re-averaged for the final score.’ Knee angle data in the sag&al plane were collected during the test using two data collection techniques simultaneously: (1) videotaping the subject and (2) using an electrogoniometer positioned at the knee joint. Videotaping method. Each subject was videotaped in the sag&al plane while performing the pendulum tests. Seven lightreflecting markers were placed as follows: (1) on the subject’s greater trochanter, (2) at the end of the upper EG arm, (3) knee joint center (on the potentiometer of the EG), (4) at the end of the lower EG arm, and (5) lateral malleolus (angle definition markers) and two on the plinth itself defining a horizontal linear measure of 40cm. The video camera was placed on a tripod and positioned such that the markers were clearly visible throughout the test and the image was as large as possible on the video monitor. A high-speed camera shutter was used to prevent “streaking” of the bright markers during the videotaping. A video time code was recorded on the audio channel to assist in the subsequent computer analysis. A computer program allowed an operator to extract the Cartesian coordinate locations of the markers in each video image of interest in each test. The video digitizing technique was similar to that reported by Abraham’ and involved the use of a video mixer, video cassette recorder, graphics tablet, and microcomputer. The Cartesian coordinates were then used to determine the knee angle at each of three points in time during the pendulum motion. These time points were: starting knee angle, first acute angle (defined as the angle where the first reversal in angular direction occurred after the leg is released), and the final resting angle. Electrogoniometer method. Each subject’s knee angle was simultaneously recorded by an electrogoniometer, placed on the lateral side of the test limb. An electrogoniometer consists of a potentiometer and two semirigid arms, connected to a DC power s~pp1y.r~The potentiometer detects changes in the angle relationship between the two arms in the form of a change in output voltage. By attaching one electrogoniometer arm to the subject’s thigh and the other to the subject’s lower leg using Velcro straps, and aligning the axis of the potentiometer with the knee flexiomextension axis, a voltage signal proportional to knee angle was recorded. The signal from the electrogoniometer was sampled at 50 samples per second by a computer using an analogue-to-digital converter and software in the LabVIEW programming environment. The determination of the knee angle from the electrogoniometer signal was achieved by calibration. This calibration method was first done by placing the electrogoniometer in two known angular positions (0” and 90”), and Arch
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Table
1: Anthropometric
Data
on 4 Subjects
Characteristic
Meall
SD
Age (vr) Height (m) Weight (kg)
28 1.74 62.5
3.37 .07 9.54
then recording these voltages by the computer. Using these two data points, it was possible for the computer to convert subsequent electrogoniometer signals from units of volts to that of degrees. An interactive computer program displayed the electrogoniometer signal on the computer screen throughout the testing. These data were stored in a computer disk file for analysis immediately following the last drop. Pilot Data Collection The pendulum test was carried out 10 times on a normal subject 23 years of age. The three simultaneous measurement methods of R2n included (1) sampling the voltage data from the EG; (2) digitizing the light reflecting markers placed on the subject’s body points, namely, greater trochanter, knee axis, and lateral malleolus (VID-Ss); and (3) digitizing the markers on the EG, namely, the ends of each EG arm and the knee axis (VID-EG). All videotaped data were digitized five times to obtain an estimate of digitization error. Study Data Collection Data were collected from a sample of four individuals who had volunteered to participate in the study. The sample consisted of three spinal cord injured individuals with spasticity and a normal subject. The subjects with spasticity were recruited such that one subject from each of the three Lyndhurst Spasticity Scale gradings participated, ie, one mild, one moderate, and one severe. The evaluation of spasticity of potential subjects was carried out by a single physiotherapist trained in the use of the Lyndhurst Spasticity Scale. The application of the scale was identical to the procedure used in normal physiotherapy practice at Lyndhurst. Only subjects who clearly fell within each of the three gradings were admitted to the study. The gradings are defined as follows: l Mild: Increased resistance to passive stretch noted but does not interfere with range of movement (ROM) or function. l Moderate: Significant resistanceof passive stretch is noted. Full ROM is not prevented; however, tone may interfere with function. l Severe: Strong resistance through passive range which is still present after several repetitions. Full ROM will be impaired and many functional skills are now impossible. The descriptive data on the subjects are listed in table 1. Five 5-drop pendulum tests were completed on all four subjects in a single session.In both parts of the study, the R2n values were calculated using the EG data and the data obtained from video digitization as outlined in the Pilot Data Collection section above. Statistical Design The following statistical analyses were employed: 1. Pilot Data: Means, standard deviations, analysis of variance (ANOVA), and Barlett tests” were calculated on the pendulum test data (R2n) from 5 digitizations of 10 pendulum tests. These pendulum tests were recorded from a single, normal subject. VID-EG and VID-Ss R2n data were used to determine the reliability of the pendulum test scores between digitizations. 2. Main Study Data: Means and standard deviations of R2n
PENDULUM
TEST
ANALYSES
Table 2: R2n Means and Estimated Standard Deviations of 5 Digftizatlons on VID-EG and VlD-Ss in 10 Pendulum Tests on a Single Normal Subject (Pilot Study Data) VIII-EG
Vld-Ss
COMPARISON,
Table
MSWl
SD
Meall
SD
1
1.12
,051
1.03
,051
2 3 4 5
1.15 1.12 1.15 1.10
,142 ,111 ,098 ,111
1.05 1.04 1.04 1.05
,051 ,038 ,042 ,048
data were obtained from 5 digitizations of 5 pendulum tests recorded from 4 subjects. Statistics performed on the main study data included intramethods Pearsoncorrelation coefficients and t statistics, interclass correlation coefficients (ICC) for each of the three methods, and a 2-way ANOVA (4 levels of spasticity and 3 levels of method of measurement) from EG, VID-EG, and VID-Ss methods. These tests were used to investigate the most appropriate placement of light-reflecting markers and to compare EG R2n data to that of VID data. RESULTS Table 2 lists the mean values (Mean) and estimated standard deviation (SD) of all 5 digitizations (Dig) in 10 pendulum tests on both VID-EG and VID-Ss. Mean R2n values for VID-EG and VID-Ss ranged from I. 10 to 1.I.5 and 1.03 to I .05, respectively. Table 3 lists the ANOVA results on 5 digitizations on a normal subject from both VID-EG and VID-Ss methods. and also lists the Bartlett test” results on standard deviations of the same digitizations. The results demonstrate that each digitizing mean and standard deviation is not statistically different from the other four. Table 4 summarizes the means and standard deviations of R2n values obtained from all 4 subjects by the three measurement methods (EG, VID-EG, and VID-Ss). Standard deviations for VID-Ss in all measurements, included in tables 2 and 4, were smaller than the values in VID-EG. Table 5 shows the Pearson correlation coefficient for each combination of two measurement methods and the degree of association between their means using t test. This result shows higher correlation between EG and VID-Ss than the same value between EG and VID-EG. Also, the t test shows that the means of EG and VID-Ss are significantly associated. The interclass correlation coefficient, which determines the reliability of each method of measurement upon 5 repeated pendulum tests on 4 subjects, demonstrated that all three methods concur. The obtained ICC values were: EG r = .998, VIDEG r = .994, and VID-Ss r = .996. With respect to the 2-way ANOVA calculated on the R2n data, the between-subjects factor was the level of spasticity, while the within group factor was the type of method used. The ANOVA values suggested no significant difference between the measures extracted by EG, VID-EG, and VID-Ss @ = ,825). Also, these results identify significant differences between the level of stiffness in any of the subjects 0, = .oO). In addition, a small interaction effect exists between the methods and the subjects’ level of stiffness 0, = 007).
SOWCl3
VID-EG VID-Ss
Bartlett Test Resuks of 5 Digitizing Data
F
p value
38 .37
,821 ,831
on R2n Means and (Pilot Study Data) X1
7.844 1.155
.097 ,885
Deviations Obtained from (Main Study Data)
EG
VID-EG
Three
VID-Ss
SD
Mean
SD
Meall
SD
1
.29
2 3 4
.31 .59 1.09
,051 ,023 ,025 ,054
.37 .30 .60 1.07
.039 .090 .036 ,060
.36 .36 58 1 .oo
,038 .061 ,017 .035
Subjects spectively,
1-3 are patients with severe, moderate, and Subject 4 is the non-SC1 subject.
and mild
spastic&y,
re-
DISCUSSION The purpose of the pilot study was to determine the consistency of the pendulum scores extracted from numerous digitizations on videotaped data. The ANOVA and Bartlett test were conducted on 5 digitization results for both VID-EG and VIDSs data to determine the association of the means and the equality of the standard deviations (table 3). The results clearly indicate that for videotaped data from the pendulum test, the videotape approach can be reliable using just a single digitization. One of the purposes of the study was to investigate the more appropriate of two placements of light-reflecting markers for videotaping angular measurements. Standard deviations of the VID-Ss data in all the measurements were lower than the value obtained in VID-EG (tables 2 and 4). It was found that the Pearson correlation coefficient between VID-Ss and EG is higher than this correlation between VID-EG and EG. Also, the association of the VID-Ss and EG means is greater in comparison with that of the VID-EG and EG means (table 5). These results suggest that using subject body points (greater trochanter, knee joint center, and lateral malleolus) as light reflector placements increases the accuracy of the videotaping method. It is apparent that small deviations from the center of the markers in digitizing affect the angular measurements. This effect is greater when the markers are close to the axis of rotation, ie, the knee. Also, it is likely that recording angular position based on markers placed on anatomic landmarks, as opposed to a device attached to the limb, would more accurately reflect the “true” knee angle. The main purpose of the study was to compare two measurement devices, electrogoniometer and videotaping. The interclass correlation coefficient for EG is slightly higher than for the videotaping. The Pearson correlation coefficient show a strong relationship between EG and videotaping (table 5). ANOVA results demonstrate significant differences between the means of the level of subjects’ muscle stiffness. These results also show a significant association between the means of scores extracted in different devices, as well as a slight interaction effect between the subjects’ level of muscle stiffness and the devices used. These results suggest that both devices are valid and reliable. Also. interaction effect suggests further study to determine whether using one of the devices is preferable for special levels of muscle stiffness. Applicability of EC and VID Methods There are advantages and disadvantages in using the pendulum test for assessingmuscle spasticity in a clinical population. 5: Intra-EG
Goniometer
p value
and Standard of Measurement
Mean
Table Table 3: ANOVA and Standard Deviations
4: R2n Means Methods
Subject
Dig NO.
1131
Jamshidi
EG’VID-EG EG’VID-Ss VID-EGWID-Ss
Pearson Correlation Coefficient Trials on 4 Subjects (Main Study
and t Statistics Data)
in 5
r
p Value
t
,995 ,999 ,997
,005
,750
.508
,001
,104
.924
,003
,510
.645
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On one hand, the test is objective and easy to administer, and its score, R2n, allows for a wide range of individual results. On the other hand, the pendulum test only measures spasticity in one muscle group, the knee extensors. The pendulum test is an effective and unbiased method of testing spasticity and hypertonia. However, its effectiveness in determining rigidity may be somewhat limited because it only reflects the knee angle at three instants of time during the test, irrespective of other factors, such as the speed or jerkiness of the movement. The present study did not intend to justify use of the pendulum test as a clinical measure of spasticity; rather, it was intended to determine the better of two methods of collecting knee angular displacement data used to calculate R2n from the pendulum test. Clearly, the results indicated that, having chosen to test spasticity using the pendulum test, both EG and VID are reliable and highly correlated methods for recording knee angles during the test. The choice then becomes which method is more appropriate for any given clinical setting. Many clinics have video equipment and there are many ways of measuring angles from a video image, including overlaying transparencies on video monitors and tracing limb positions at each of the three angle positions during the test. A simple electrogoniometer can be constructed from inexpensive mechanical and electronic parts. Most clinics have computers that could be used with either video or electrogoniometers. Our results suggest that clinicians interested in measuring spasticity using the pendulum test can use either video or electrogoniometry with confidence.
CONCLUSIONS The results elicited from this study enable us to make the following conclusions: 1. In the videotaping method, using one digitization by a single operator is sufficient. 2. The appropriate placement of light-reflecting markers in videotaping are on body points. 3. Electrogoniometer and videotaping are both reliable, highly correlated, and interchangeable in measuring spasticity in the pendulum test. However, using EG for further
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studies is suggested. EG is less expensive and more beneficial in contrast to the time spent in tape digitization or the high cost of an automated digitizing system. Also, according to the results of this study, the use of EG is more reliable. Acknowledgment: Sincere gratitude is expressed to Elaine Aimone for her clinical advice. Special appreciation is also expressed to Mahmoud &repour for his assistance with the statistical aspects of this project, Herman Whitlock for the construction of the electrogoniometer, and Andrea Lee for her technical assistance. This study was supported by the Lyndhurst Hospital Foundation and the A. T. Jousse Laboratory Endowment Fund. References 1. Wartenburg R. Pendulousness of the legs as a diagnostic test. Neurology 1949; 1:18-24. 2. Bajd T, Vodovnic L. Pendulum testing of spasticity. J Biomed Eng 1984;6:9-16. 3. Robinson CJ. Spasticity in spinal cord injured patients: 2. Initial measures and long term effects of surface electrical stimulation. Arch Phys Med Rehabil 1988:69:862-g. 4. Katz RT, Rovai GP, Brait C, Rymer WZ. Objective quantification of spastic hypertonia: correlation with clinical findings. Arch Phys Med Rehabil 1992;73:339-47. 5. Goodwin J, Clark C, Deakes J, Burdon D, Lawrence C. Clinical methods of goniometry: a comparative study. Disabil Rehabil 1992; 14:10-5. 6. Stillman B, McMeeken J. A video-based version of the pendulum test: technique and normal response. Arch Phys Med Rehabil 1995; 76: 166-76. I. Bohannon RW. Variability and reliability of the pendulum test of spasticity using a Cybex II isokinetic dynamometer. Phys Ther 1987;67:659-61. 8. Levin MF, Hui-Chan C. Are H and stretch reflexes in hemiparesis reproducible and correlated with spasticity? J Neurol 1993;240:6371. 9. Abraham L. An inexpensive technique for diaitizina spatial coordinates from videotape. In: Jonsson-B, edito;. Biomechanics X-B. Chamuaimi (JL): Human Kinetics Publishers. Inc.. 1987:1107-10. 10. Winter DA. Biomechanics and motor control of human movement. New York: John D. Wiley and Sons, 1990. 11. Montgomery C. Design and analysis of experiments. New York: John D. Wiley and Sons, 1991. I
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