Test-Retest Reliability of The Sensory Organization Test in Noninstitutionalized Older Adults

Transcription

1 77 Test-Retest Reliability of The Sensory Organization Test in Noninstitutionalized Older Adults Cheryl D. Ford-Smith, MS, PT, Jean F. Wyman, PhD, RN, R.K. Elswick, Jr., PhD, Theresa Fernandez, MS, RN, Roberta A. Newton, PhD, PT ABSTRACT. Ford-Smith CD, Wyman JF, Elswick Jr, RK, Fernandez T, Newton RA. Test-retest reliability of the sensory organization test in noninstitutionalized older adults. Arch Phys Med Rehabil 1995;76: The purpose of this study was to determine the 1-week test-retest reliability of the Sensory Organization Test (SOT), using computer-generated scores and loss of balance (LOB) episodes in noninstitutionalized older adults. The SOT was administered to each subject on two separate days 1 week apart in an out-patient clinic. A volunteer sample of 40 individuals who were at least 65 years of age participated in this study. The main outcome measures were computer-generated scores for the first trial and the average of the three trials in each of the six sensory conditions of the SOT; computer-generated composite score of the six conditions; LOB on the first trial and any of three trials in each condition. The intraclass correlation coefficients (ICC) for the SOT first trial data ranged from.15 in Condition 3 to 0.70 in Condition 5. The ICCs for the SOT average of three trials ranged from 0.26 in Condition 3 to 0.68 and 0.64 in Conditions 5 and 6. Percent agreement was 77% to 100% for LOB on the first trial, as well as LOB on any of three trials of Conditions 1 through 6. As the conditions became more difficult, an increasing number of subjects experienced LOB. Analysis revealed fair to good test-retest reliability for computer-generated scores and good reliability for LOB across some conditions of the SOT. A modification to the current scoring system is suggested which would improve the reliability of the computer-generated scores of the SOT by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Balance problems may be associated with impaired abifity to integrate the visual, proprioceptive, and vestibular systems for determination of body position in space. Inability to use these" systems appropriately may be related to disease, trauma, or changes occurring in the aging brain.' In the older adult, it is important to distinguish the balance problems associated with decline in the receptivity of both the sensory and motor systems from balance problems associated with aging or pathologic processes) Several balance tests are being used to delineate the underlying processes associated with balance. Some clinical tests, such as the Functional Reach Test 3 or the Balance Subscale, 4 are simple and easy to administer. The Functional Reach Test has good test-retest reliability, whereas the Balance Subscale has high interrater agreement. More sophisticated tests using a computerized force platform are now being done clinically to obtain diagnostic information for different individuals, but few test-retest reliability studies have been performed. Goldie and colleagues 5 examined the retest reliability of computerized stable platform measurements of vertical force and center of pressure. Subjects were tested twice From the Department of Physical Therapy (Ms. Ford-Smith), School of Nursing (Dr. Wyman, Ms. Fernandez), Department of Biostatistics (Dr. Elswick), Medical College of Virginia, Virginia Commonwealth University, Richmond, VA; Department of Physical Therapy (Dr. Newton), Temple University, Philadelphia, PA. Submitted for publication January 7, Accepted in revised form August 8, Research supported by the National Institute of Nursing Research, Grant R01 NR02561, Geriatric Leadership Academic Award, National Institute on Aging, Grant 5R07A G00404, and a Special Grants-In-Aid from Virginia Commonwealth University. No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors or upon any organization with which the authors are associated. Reprint requests to Cheryl D. Ford-Smith, MS, PT, Route 2, Box 3636, Bumpass, VA by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation /95/ /0 on seven stance positions with a 10-minute break between the test s~si0ns. The: authors: reported that force measures were mor~ reliable than center of pressure in numerically identifying postural unsteadiness. Other researchers and clinicians are using moving computerized platforms to assess dynamic postural responses, sensory interaction on balance, and effectiveness of treatment intervention. There is limited information, however, on the reliability of moving platform measures. Manufacturers have reported high intratrial reliability in control subjects, but there is no information on the test-retest reliability of measurements obtained on different days. 6 Nashner 7 has developed the Sensory Organization Test (SOT), which includes six sensory conditions, to evaluate a person's standing balance. The SOT is administered with a computerized system using a movable dual forceplate and a movable visual screen (EquiTest). The SOT protocol assesses the patient's ability to make effective use of visual, vestibular, and proprioceptive inputs, as well as the patient's ability to suppress inaccurate sensory information. Differences in the amount of body sway under the different sensory conditions determine the patient's ability to organize and select the appropriate sensory information to maintain postural control] Computerized dynamic posturography such as the SOT has gained wide acceptance as a method of measuring posrural control. TM Until test-retest reliability is established, however, the diagnostic information gathered from the tool may be negligible in determining the effectiveness of treatment intervention or the success of rehabilitation methods. With the increasing incidence of falls among the elderly, it is crucial to use reliable balance tests to identify individuals at risk for falling and to design effective prevention techniques and intervention programs. Our purpose, therefore,

2 78 RETEST RELIABILITY OF THE SOT, Ford-Smith Table 1: Sensory Organization Test Conditions Condition Vision Screen Surface Absent Absent was to determine the 1 week test-retest reliability of the SOT using computer-generated scores and loss of balance episodes in noninstitutionalized older adults. METHOD Subjects A volunteer sample of 40 individuals (30 women and 10 men) participated. Subjects were at least 65 years of age (~ = 74.8; SD = 3.6) and noninstitutionalized, without hip or knee replacements, ambulatory without a quad cane or walker and mentally intact (Mini-mental State Scores > 2312). Visual acuity was less than or equal to 20/70 and subjects were free from any progressive neurologic, vestibular, severe cardiovascular or musculoskeletal disease. The majority of subjects were white (83%, n = 33), with a college education (63%, n = 25). More than half of the subjects reported exercising at least 3 times a week (63%, n = 25) and walked without a straight cane (98%, n = 39). One subject reported using a straight cane occasionally. Forty percent had fallen in the past year. directly above the intersection of the X and Y axes. The corner transducers measure vertical forces. The center transducer measures shear forces in the plane parallel to the floor. Three servomotors move the forceplates and visual screen within a range of _+10. The forceplates rotate at a maximum velocity of 50 per sec and the screen rotates at a maximum velocity of 15 per sec. Surface forces are recorded through a second-order digital low-pass tilter to obtain the position of the vertical projection of the COG. 13 Calculations are made using a Dell System 210 b personal computer with Samtron VGA color monitol~ using Equitest version 4.0 software. Platform and screen movements were set at a gain of 1.00 to exactly match subject A/P sway excursions. A computer-generated graphic printout shows the equilibrium score for each trial. The equilibrium score is the angular difference between the subjects calculated maximum A/P COG displacements and the theoretical maximum of Each trial is scored separately, with equilibrium scores expressed as a percentage ranging from 0 to 100. Equilibrium scores near 100 theoretically indicate no A/P excursion, and scores approaching 0 indicate an increase in A/P excursion. 6 The trial was stopped by the operator when subjects exceeded their limits of stability and took a step, opened their eyes (if the condition required eyes closed) or grabbed an object or person to maintain upright stance. Interrupted trials were considered a fall Instrumentation The SOT protocol consists of six independent sensory conditions (table 1). Each condition has three 20-second trials. In Condition 1, no altered sensory stimuli are given. In Condition 2, visual stimuli are removed by instructing the subject to close his/her eyes. In Condition 3, visual stimuli are altered by moving the visual screen with the subject's anterior/posterior (A/P) sway, thus maintaining the visual field a constant distance from the subject's eyes. In Condition 4, proprioceptive stimuli are altered by rotating the platform with the subject's sway, thus maintaining a constant angle at the ankle joint. In Condition 5, proprioceptive stimuli are altered and visual stimuli are absent; the subject's eyes are closed and the platform moves with the subject's sway. In Condition 6 of the test battery, proprioceptive and visual stimuli are both altered by moving the platform and visual screen with the subject's sway. The SOT protocol was administered using the Equitest System, which consists of a movable dual forceplate, a movable visual screen and an overhead safety bar with safety straps. The dual forceplate consists of two 9 18 footplates connected by a pin joint. The two footplates have four force transducers (strain gauges) mounted symmetrically under the footplates on a supporting center plate, and a fifth transducer is bracketed to the center plate directly beneath the pin joint. The force transducers are placed so that when a subject stands with ankles centered over the placement strip on the dual forceplate, with feet an equal distance laterally from the center line, his or her center of gravity (COG) is located Patient position during testing on the EquiTest S y s t e m.

3 RETEST RELIABILITY OF THE SOT, Ford-Smith 79 Table 2: Sensory Organization Test Scores (N = 40) First Trial Average of 3 Trials Test Retest Test Retest Condition Mean SD Mean SD Mean SD Mean SD ,8 5 42,4 29, , , , , ,2 (LOB) and given a score of zero by the computer. A composite score was calculated by independently averaging the scores for Conditions 1 and 2, adding these two scores to the equilibrium scores from each trial of Conditions 3, 4, 5, and 6, and dividing the sum by Procedure After a brief explanation of the study, each subject signed a consent form and underwent a comprehensive assessment that included history and physical examination, functional evaluation, psychosocial assessment, strength and flexibility testing, and balance assessment. This information was gathered as part of a larger study funded by the National Institute for Nursing Research. The SOT was administered on 2 separate days 1 week apart. Subjects stood on the force platform without shoes, faced the visual screen, and wore a safety harness (fig). Subjects were instructed to stand with their feet a comfortable distance (approximately 6 to 8 inches) apart during testing, and not to touch the visual screen or move their feet. The medial malleoli were placed over the placement strip imprinted on the platform. Subjects were allowed to rest between test conditions on request. DATA ANALYSIS Clinicians have interpreted the SOT results in a variety of ways, comparing first trial scores across each condition, averaging the trials across each condition, or comparing changes in composite scores and the number of LOB episodes across each condition. Therefore, we report on each of these methods, comparing the computer-generated scores from 1 week to the next. For the continuous variables, intraclass correlation coefficients (ICC 3,1) TM were estimated for the first trial of each condition, the average of the three trials for each condition and the composite score, as a measure of test-retest reliability. Also, the confidence interval was calculated for each. Table 3: Reliability of the Sensory Organization Test Scores: ICC and CI First Trial Only Average of 3 Trials Condition ICC 90% CI ICC 90% CI , , , , , , , , , , , ,.77 The confidence interval (CI) serves two purposes. First, it may be used to test the null hypothesis that the ICC is equal to zero (ie, the test-retest data is unreliable). If zero is included in the CI, this null hypothesis is accepted. 15 The second and more important purpose of the confidence interval is to provide information on the limits of uncertainty surrounding the estimated ICCs. For the dichotomous variables, falls on the first trial of each condition and falls on any trial of each condition, percent agreements and Kappa coefficients (where possible) were computed] 6 RESULTS Sensory Organization Test Scores We first determined whether the scores on the first trial (table 2) of each condition were consistent between the two testing periods. The ICC for the SOT first trial data ranged from 0.15 in Condition 3 to 0.70 in Condition 5 (table 3). We also determined whether the SOT was consistent in measuring average balance performance over the three trials (table 2). Conditions 1 to 2 and 4 to 6 exhibited fair to good reliability. The ICCs for the SOT average of three trials ranged from 0.26 in Condition 3 to 0.68 and 0.64 in Conditions 5 and 6. The SOT composite score exhibited good reliability with an ICC of 0.66 (CI 0.49, 0.79) (table 3). Loss of Balance Percent agreement ranged from 77% to 100% for LOB on the first trial (table 4), as well as LOB on any of three trials of Conditions 1 through 6. No subjects experienced LOB on Conditions 1 and 2. Two subjects exhibited LOB on the first trial of Conditions 3 and 4 in the first testing session. As the conditions became more difficult, an increasing number of subjects experienced LOB. Conditions 1 to 4 showed low variability in subject performance, and therefore a Kappa coefficient could not be calculated. Percent agreement and Kappa coefficients for Conditions 5 and 6 for LOB on the first trial and any of the three trials were similar, though the agreement was slightly higher for LOB on the first trial. DISCUSSION This is the first report of test-retest reliability of the computer-generated scores for the SOT with noninstitutionalized older subjects. Our subjects were similar to the general older population with respect to gender and incidence of falls.

4 80 RETEST RELIABILITY OF THE SOT, Ford-Smith Table 4: Loss of Balance (LOB) on the Sensory Organization Test LOB on First Trial Condition Test ReTest Agree (%) KAPPA Test LOB on Any Trial Retest Agree (%) KAPPA * * * * * * * * * Unable to calculate KAPPA N = 40 Demographically, 68% of older adults are women 17 and 30% to 50% of older adults without pathology fall yearly. TM Generally, using Fleiss s criteria 4 (less than 0.4 poor, 0.4 to 0.75 fair-to-good, and 0.75 and above excellent reliability), the SOT showed poor-to-good 1-week test-retest reliability across the six sensory conditions. The first three conditions of the SOT protocol seem to lack the sensitivity to detect differences between older adults who do not have underlying pathology. Conditions 1 and 2 varied little across subjects and may be best used as a record of baseline performance. A good example of the value of the confidence interval is provided by the ICC from Condition 1 first trial data. The estimated ICC was 0.57 which, according to the Fleiss guidelines, represents good reliability; however, the lower 90% confidence limit, which may be thought of as a lower bound was 0.37, which suggests reliability in the poor range) 9 Condition 3 consistently showed poor reliability (ICC of.15 and.27) in first trial scores and average scores. This condition may be ineffective in altering visual stimuli, and that may contribute to the lack of variation in performance seen on the condition. When overall performance was analyzed, however, the SOT composite score had good reliability (ICC of 0.66). SOT scores in this study may not have been reliable because the scoring system of the SOT does not differentiate subjects who show a high amplitude A/P sway from subjects who are able to stand at the end of their limits of stability until the last few seconds of the trial. The subject who sways constantly during the entire trial may obtain a score above zero, whereas the subject who stands steady until the second before the end of the trial and then falls will get a score of zero. These preliminary data suggest that the SOT protocol has potential for detecting instability in older adults and identifying those conditions that may place an older individual at risk for falling. The Equitest's SOT protocol, however, would be more statistically reliable if subjects were given a score for their effort to remain standing on a given trial, even though they might fall during that trial. A suggested modification of the current scoring system would be to use 1 the equilibrium score obtained approximately ~ second before a fall occurs. A weighted score could then be constructed by multiplying the equilibrium score by the percent time of the 20-second trial that the subject remained standing. This weighted score would improve the reliability and make the test more sensitive for assessing patient improvement after intervention. Thus, the SOT would become a more valuable clinical instrument. LOB occurred more frequently in Conditions 5 and 6, in which visual and proprioceptive inputs are distorted. This finding is in agreement with that of Wolfson and colleagues, n who suggest that impaired vestibular input may affect postural control in older adults. LOB in earlier conditions would suggest that other systems are also involved, such as joint range of motion and muscle force production. Our observation has been that older adults have a limited arc of motion about the ankles, which may contribute to decreased limits of stability. Interestingly, in Conditions 5 and 6 subjects fell less frequently in their second session then in the first. However, this finding may be linked to decreased anxiety about the testing protocol. A number of subjects said they were more comfortable in the second session because they knew what to expect. A lower anxiety level may account for the higher mean SOT scores in the second session. In conclusion, the results provide evidence of fair to good test-retest reliability across some conditions of the SOT. Reliability differs depending on how performance is evaluated on the SOT. Using the manufacturer's current scoring system, scores have only poor to good reliability. The findings in this study suggest that the composite score and number of LOB episodes may be most useful in assessing balance performance and treatment effectiveness. References 1. Medlin K. Sensory motor integration in the aging brain. Neurol Report 1991; 15(3): Newton RA, Deo A. Standing balance in elderly adults with and without hearing impairments. Proceedings of the World Confederation for Physical Therapy 1 lth International Congress, London, England, 1191 ; Duncan PW, Weiner DK, Chandler J, Studenski S. Functional reach: a new clinical measure of balance, J Gerontol 1990;45:M Tinetti ME. Performance-oriented assessment of mobility problems in elderly patients. J Am Geriatr Soc 1986;34: Goldie PA, Bach TM, Evans OM. Force platform measures for evaluating postural control: reliability and validity. Arch Phys Med Rehabil 1989;70: Equitest System Data Interpretation Manual. NeuroCom International, Inc, Clackamas, OR, 1991: Nashner LM, Peters, JF. Dynamic posturography in the diagnosis and management of dizziness and balance disorders. Diagn Neurotol 1990;2: Mirka A, Black O. Clinical application of dynamic posturography for evaluating sensory integration and vestibular dysfunction. Neurol Clin 1990; 8(2): Norre ME, Forrez G, Beckers A. Posturography measuring instability in vestibular dysfunction in the elderly. Age Aging 1987; 16: Lichtenstein MJ, Shields SL, Shiavi RG, Burger MC. Clinical determinants of biomechanics platform measures of balance in aged women. J Gerontol 1988; 36:

5 RETEST RELIABILITY OF THE SOT, Ford-Smith Wolfson L, Whipple R, Derby C, Amerman P, Murphy T, Tobin JN, et al. A dynamic posturography study of balance in healthy elderly. Neurology 1992;42: Folstein MF, Folstein SE, McHugh PR. Mini-mental; state: a practical method for grading the cognitive state of patients for the clinician. J Psychiatr Res 1975; 12: Equitest Operator's Manual. Version 4.0. NeuroCom International, Inc, Clackamas, OR, pp F1-F Shrout PE, Fleiss, JL. Intraclass correlations: Uses in assessing rater reliability. Psychol Bull 1979;36: Bhattacharyya GK, Johnson RA. Statistical concepts and methods. New York: Wiley, 1977: Landis JR, Coch GG. The measurement of observer agreement for categorical data. Biometrics 1977;33: Myers GC. Demography of aging. In: Binstock RH, George LK, editors. Handbook of aging and social sciences. San Diego: Academic Press, 1990: Tideiksaar R. Falling in old age: its prevention and treatment. New York: Springer-Verlag, Fleiss JL. The design and analysis of clinical experiments. New York: Wiley, 1985:8-14. Suppliers a. NeuroCom International, Incorporated, 9570 SE Lawnfield Road, Clackamas, OR b. Dell Computer Corporation, 9505 Arboretum Boulevard, Austin TX c. Samsung Electron Services America, Incorporated, East Firstone Boulevard, Suite 101, Lamerada, CA