Sitting Balance: Its Relation to Function in Individuals With Hemiparesis

Transcription

1 865 Sitting Balance: Its Relation to Function in Individuals With Hemiparesis Deborah S. Nichols, Phi), PT, Laura Miller, MS, PT, Lynn A. Colby, MS, PT, William S. Pease, MD ABSTRACT. Nichols DS, Miller L, Colby LA, Pease WS. Sitting balance: its relation to function in individuals with hemiparesis. Arch Phys Med Rehabil 1996;77: Objectives: To evaluate test-retest reliability of sitting balance measures in healthy subjects and individuals with hemiparesis secondary to stroke, to evaluate the ability of the balance measures and Functional Independence Measure (FIM) to document changes over time, and to compare changes in the balance measures and FIM to each other. Method: Six nonpatient subjects were evaluated for testretest reliability. Fourteen subjects with hemiparesis were tested every 2 weeks during their hospitalization on their ability to lean to either side, lean forward, and maintain a symmetrical posture. Maximum displacement was recorded using the Balance System. FIM scores were obtained for each testing session. Results: Test-retest reliability for nonpatient subjects was high and for patients was moderate to high. Leaning forward and to the paretic side showed the greatest number of correlations with the FIM scores. All of the FIM scales and the forward lean measure documented progress. Conclusions: The protocol developed to test sitting balance, using the Balance System, seems appropriate for use with patient populations. The ability to lean maximally to either side or forward or sit symmetrically is not strongly related to function by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation p ERSONS who suffer a cerebrovascular accident (CVA) often have resultant functional Ioss,~'2 manifested as deficits in ambulation and self care. Frequently, physical therapists focus initial therapy on relearning components of movement that are assumed to be necessary for the acquisition of functional skills. 3'4 An example of this is sitting balance. Sitting balance is not a functional activity, but the ability to maintain or attain sitting balance is believed to be necessary to perform functional activities such as dressing, transferring, and eating 3'5'6 in a seated position. Although studies have shown that sitting balance is one of many good predictor variables for functional outcome after a CVA, 7-11 there is, unfortunately, no widely accepted or standardized measurement of this precursor to seated functional activities. Measurement techniques have included the assessment of trunk movements, 9 perturbations, 7 and a variety of subjective From the Physical Therapy Division, School of Allied Medical Professions, The Ohio State University (Dr. Nichols, Ms. Miller, Ms. Colby), and the Department of Physical Medicine and Rehabilitation, The Ohio State University (Dr. Pease), Columbus, OH. Submitted for publication September 5, Accepted in revised form March 18, 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 Deborah S. Nichols, PhD, PT, 1538 Perry Street, Columbus, OH by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation /96/ /0 ratings. 7'9'~2'j3 Various studies have suggested that refining measurements of predictor variables such as sitting balance may allow for a more accurate prediction of functional outcome.9' ~.~4 The ability to maintain one's balance requires postural control, ~5 which limits the body's sway and keeps its center of gravity within its base of support. 15'~6 This control allows an individual to maintain balance when body movements occur. In standing, the muscle activity associated with postural control can occur at the head, pelvis, or ankle~3'14; however, in sitting without trunk support, postural control occurs mainly at the pelvis./3 Biomechanically, specific trunk movements have to occur to maintain postural control in sitting. 3'4'17 When weight is shifted in any plane, the trunk responds with a movement to counteract the change in the center of gravity. This countermovement or counteraction results in the center of gravity staying within the base of support and the maintenance of a sitting position. 3'4'j7 Postural control in sitting has been measured using trunk movement, 9'~z'~3 perturbations 7 or ordinal scales of sitting balance. 7,~z These methods have been used in the assessment of postural control, but in addition, force platforms have been used to measure steadiness (the ability to demonstrate minimal body motion or sway), ~8'j9 symmetry (the ability to demonstrate even weight distribution), 2 and dynamic stability (the ability to transfer weight within the base of support). 21"22 Force plates are a valid and reliable measure of these components of postural control in standing) 3 Such studies have not been done on the use of force plates for the evaluation of steadiness, symmetry, and dynamic stability in sitting. The Balance System a is a force platform system that is commercially available for the evaluation of balance. Although it was designed for the evaluation of balance in standing, the manufacturer suggested that it could also be used to evaluate sitting balance) 4 No previous research has been conducted on the reliability and validity of the Balance System in the evaluation of sitting balance, however. The purpose of this study was to: (1) evaluate test-retest reliability of sitting balance measures in both healthy young subjects and individuals with hemiparesis secondary to stroke; (2) evaluate the ability to document change in sitting balance measures over time in individuals with hemiparesis secondary to stroke; and (3) compare changes in sitting balance measures to changes in functional skill abilities as identified by the Functional Independence Measure (FIM). Subjects METHODS On admission to our university's Rehabilitation Center 14 subjects who met the following selection criteria were recruited for participation in this project: (1) hemiparesis secondary to first CVA within the last 6 months; (2) nonfunctional ambulation (unable to ambulate independently for at least 10 feet); (3) medically stable; (4) ability to understand verbal commands; (5) oriented to name, time, and place; (6) no vestibular or orthopedic disorders that could affect balance. Of the 14 subjects, 12 (11 men, 1 woman) completed testing;

2 866 BALANCE AND FUNCTION IN HEMIPLEGIA, Nichols 2 were dropped from the project because of medical complications. Nine subjects had left hemiparesis; 3 had right hemiparesis. Subjects ranged in age from 34 to 72 years (mean = 65.5, SD = 11.9). The time elapsed from the onset of the subjects' CVA and admittance to the hospital ranged from 4 to 33 days (mean = 15, SD = 10.3). The protocol was approved by our University Biomedical Sciences Human Subjects Review Committee, and all subjects provided informed consent prior to participation. Instrumentation The Balance System was used to assess weight shift and symmetry in sitting. This system is a computerized force platform system with four adjustable force transducers, which measure vertical force only. Center of force data is expressed as a percent change in body weight distribution. Assessment of each subject' s functional level was determined using the FIM, an 1 8-item assessment tool that evaluates patient performance of activities of daily living, including dressing upper body, dressing lower body, transfers, locomotion/walking, and locomotion/wheelchair mobility as well as cognitive function. 25 The FIM demonstrates face ~3 and construct 26 validity as well as high internal consistency 26 and interrater reliability with individuals trained in its administration. 2'27 The FIM scores were taken from the patient's medical record. The FIM is administered to all inpatients on admission to the rehabilitation center, every 2 weeks during hospitalization, and again upon discharge by members of the rehabilitation staff who have been trained in its administration and certified by the developers of the test. Thus, although reliability was not established as part of the project, the raters have been determined to be reliable by the test developers as part of the certification process. Pilot Reliability Study Six nonpatient subjects were recruited to evaluate test-retest reliability for the postural control protocol, since the Balance System had not previously been used to evaluate sitting postural control. The testing protocol was the same as that used for testing the subjects with hemiparesis. Testing consisted of a single testing session with 3 trials of each of the 4 conditions (symmetrical, lean right, lean left, lean forward). Postural Control Measurement Procedures All subjects were tested within 4 days of their admission to the rehabilitation unit. Subject characteristics (age, medical history, and date of CVA) were obtained before and during this session. This information was gathered from the patient, family interviews, and the medical record. Subjects were seated on a firm chair with adjustable legs. A force transducer was placed under each leg of the chair. These transducers were marked with a circle in the center, in which the chair leg was placed, to assure consistent placement between testing trials and sessions. The chair was adjusted so that the subject's hips and knees were in a transverse plane. The greater trochanters of each subject were marked while the subject was standing. These marks were lined up along specific marks on the chair to assure similar positioning for each subject. The subject's feet were fiat on the floor with the feet and knees (mid-pateua) positioned in line with the anterior superior iliac spines. Testing consisted of 3 trials of each of 4 conditions, ordered as follows: symmetrical, lean right, lean left, and lean forward. During the symmetrical condition, subjects were instructed to sit symmetrically with their trunk centered. During the leaning conditions, they were instructed to lean as far as possible in each direction without forward flexion or rotation. The experimenter stood nearby to spot the subject during the leaning trials to prevent falls. Each trial lasted 10 seconds. After completing the first and second trials of each condition subjects were assisted in standing up and sitting back down before the next set of trials. They were allowed to rest as needed. Postural control was assessed using the protocol described above every other week during the patient's hospitalization. Testing for each individual was conducted at the same time on the same day of the week. FIM scores were obtained at discharge from the medical record. Each subject underwent 3 balance testing sessions, and three FIM scores were obtained for each subject, which corresponded in time with the testing sessions. Data Analysis Postural control data for the amount of weight shift a subject was able to perform was recorded as the percentage of body weight shifted, which is the unit of measure for the Balance System. A difference score was calculated and recorded, comparing the percentage body weight shifted from the symmetrical position to the shifted position (right, left, forward). Higher scores were associated with greater weight shift. The symmetrical condition was compared to a neutral position, in which equal weight (50%) would be placed on each set of force transducers. Thus, a subject who was leaning to the left would have greater than 50% of his weight on the left; 50% was then subtracted from the recorded percentage to obtain a difference score. Subjects with symmetrical weight distribution could receive a score of 0. Thus, lower scores signified better symmetry. The recording of the postural control data was the same for both the normal subjects and the subjects with herniparesis. The FIM is scored on a 7-point scale with a score of 1.0 indicating dependent function on a given scale and a score of 7.0 indicating independent function on a given scale. Five of the FIM scales were used: dressing upper body, dressing lower body, transfers, locomotion/walking, locomotion/wheelchair. These scales were chosen because trunk control is considered to be an important aspect of independent function in these skill areas. The postural control data were determined to be ordinal data and thus were analyzed using parametric statistics, lntraclass correlation coefficients (2,1) were determined for each postural control testing condition (symmetrical, lean right, lean left, lean forward) to evaluate test-retest reliability for both the nonpatient subjects and subjects with hemiparesis. These were computed for all three trials and for trials two and three only. The FIM scores were determined to be interval data; therefore, a nonparametric analysis was used to compare the FIM and postural control measures. First, in this analysis, the leans to the left and right were identified as being toward the nonparetic or paretic side. Then, Spearman rank correlation coefficients were calculated between the mean score for each of the four postural control conditions (symmetrical, lean to the paretic side, lean to the nonparetic side, lean forward), as measured on the Balance System, and each of the five selected FIM scores (dressing upper body, dressing lower body, transfers, locomotion/walking, locomotion/wheelchair) for the three time intervals. Friedman's test was used to determine if a significant change occurred over time in the postural control scores and the five selected FIM scores. Alpha was set a priori at.05. Reliability. RESULTS Test-retest reliability for the nonpatient subjects was extremely high (symmetrical ICC =.86, lean right ICC = Arch Phys Med Rehabi! Vol 77, September 1996

3 BALANCE AND FUNCTION IN HEMIPLEGIA, Nichols 867 Table 1: Intraclass Correlation Coefficients for Subjects With Hemiparesis on Balance System ICCs: All 3 Trials ICCs: Trials 2 & 3 Time Time Condition Symmetrical Lean to paretic side Lean to nonparetic side Lean forward , lean left ICC =.92, and lean forward ICC =.96). Testretest reliability for the subjects with hemiparesis was moderate to high with slightly higher ICCs computed when only trials 2 and 3 were used (table 1). This suggests a slight learning effect between trial 1 and 2. Comparison of Balance System to FIM. Table 2 lists the Spearman rank correlation coefficients for the three testing sessions between each of the postural control conditions and the FIM scales. Correlations ranged from.01 to.69. Leaning forward and to the paretic side showed the greatest number of significant correlations with the FIM scores. Friedman's test for change over time. Change over time for both the postural control conditions and the FIM was assessed by using Friedman's test (table 3). A significant amount of change was identified for all of the FIM scales and for the forward lean condition. The other postural control conditions (symmetrical, lean to the paretic side, lean to the nonparetic side) did not show significant change over the course of the study. Although the postural control scores could have been evaluated by using an analysis of variance, Freidman' s test was used for consistency. This may have resulted in slightly more conservative p values but should not have altered the results. DISCUSSION Reliability The results of the pilot study with the nonpatient subjects yielded high test-retest reliability over the three trials, which supports the use of this type of testing protocol for the evaluation of postural control in sitting, using the Balance System. Further test-retest reliability for the subjects with hemiparesis, although lower than that for the nonpatient subjects, was still moderate to high, suggesting that the lower correlations were Table 2: Correlations Between Balance System Measures and FIM Scores FIM Scores Postural Control Condition DU DL T W C Testing Session 1 Symmetrical Lean to Paretic Side.38.49".55*.29.59* Lean to Nonparetic Side Lean Forward.58*.59*.60*.05.57* Testing Session 2 Symmetrical Lean to Paretic Side Lean to Nonparetic Side Lean Forward Testing Session 3 Symmetrical * Lean to Paretic Side.62*.63*.42.51".23 Lean to Nonparetic Side.47.51" Lean Forward.55".69* Abbreviations: DU, FIM dressing upper body score; DL, FIM dressing lower body score; T, FIM transfers bed/chair/wheelchair score; W, Iocomotion/walking score; C, locomotion/wheelchair score. * p <.05. secondary to inconsistent performance on the part of the subjects with hemiparesis and not due to the testing protocol. Subjects with hemiparesis have previously been found to move less consistently than nonpatient peers. 28 Comparison of the Postural Control Measures to the FIM The results from the correlational analysis suggest that there is no relationship between the ability to sit symmetrically or lean to the nonparetic side and functional skills such as dressing, transfers, and mobility (either ambulation or wheelchair propulsion) as measured by the FIM. However, there does seem to be some relationship between the ability to lean forward and to the paretic side and these same functional activities. On admission, leaning forward did not correlate with walking but did correlate with the other FIM scores. This should not be surprising because a forward lean is not a component of walking but is typically a component of dressing, transfers, and wheelchair propulsion. In addition, on admission to the hospital, the ability to lean to the nonparetic side correlated with three FIM scores: dressing lower body, transfers, and wheelchair propulsion. It is interesting that by 2 weeks into intensive rehabilitation there were no significant correlations between the postural control measures and FIM scores. This may best be explained by the focus of therapy that these patients receive as compared to the protocol for postural control assessment used in the present study. The goals of therapy for patients with hemiparesis typically focus on consistent performance of motor skills and not maximal movement in any direction. 29 It is evident from the examination of the intraclass correlational analysis that symmetrical sitting was more consistent during the second testing session, conducted 2 weeks into the rehabilitation stay, than during the first or last testing sessions. Thus, therapy must be emphasizing symmetrical sitting during those first 2 weeks; maximal leaning may actually be discouraged during this time period as it may be unsafe. By discharge, significant correlations were again seen between the postural control measure for lean to the paretic side and both dressing scores (upper and lower body) and wheelchair propulsion; however, the correlation for transfers, although moderate was not significant (r =.42, p =.08). Similarly, the correlations between the lean forward measure and the dressing scores were also significant, but the correlations for transfers and wheelchair propulsion were not significant. This suggests that by discharge from the inpatient rehabilitation program, patients with hemiparesis have learned strategies for controlling their balance that allow them to move farther in the direction of their paretic side. Sandin and Smith 7 found that weekly sitting balance assessments strongly correlated with weekly Barthel Index scores (another measure of function) throughout the rehabilitation stay Table 3: Changes in Scores Over Time Friedman's Test Score Balance System Symmetrical Lean to paretic side,17.92 Lean to nonparetic side Lean forward FIM Scores DU DL T W C Abbreviations: DU, FIM dressing upper body score; DL, FIM dressing lower body score; T, FIM transfers bed/chair/wheelchair score; W, locomotion/walking score; C, locomotion/wheelchair score. p

4 868 BALANCE AND FUNCTION IN HEMIPLEGIA, Nichols for patients with hemiparesis secondary to stroke. The correlations at admission and discharge in our study mirror the Sandin and Smith findings; however, there were no significant correlations at the second testing session. This discrepancy is most likely due to the difference in the balance measures used in the two studies. Sitting balance was assessed in the Sandin and Smith study using a 4-point subjective scale, which rated the patient's response to external perturbations; this type of activity is frequently used in the treatment of neurological patients throughout their hospitalization. This study used a maximal lean protocol and measured the percent change in body weight displacement; as discussed earlier, this type of movement may not be part of the early stages of rehabilitation and may even be discouraged. Change Over Time There was no significant change in the ability to sit symmetrically or to lean to either the paretic or nonparetic side over the course of the study as measured by the Freidman test. There was, however, a significant change in the ability to lean forward and in all of the FIM scores. It seems likely that the lack of change in the former measures and the significant change in the latter measures reflect treatment goals. Acquisition of functional skills is the primary focus of any physical therapy program; further, a forward lean is a component of many functional skills (coming to standing, dressing, wheelchair propulsion, etc). This relationship was partially supported in the correlational analysis in the present study, which found a moderate relationship between our forward lean measure and the dressing scores (upper and lower body) from Test 1 and Test 3 as well as the transfer score from Test 1 only. A stronger relationship was expected; however, the protocol measured the patient's ability to perform a maximal forward lean without loss of balance. Although this type of lean may be important for donning and doffing shoes, it appears not to be necessary for most functional activities (transfers, wheelchair propulsion, ambulation). The same is most likely true for the other postural control measures used in this study. Although the ability to lean to the paretic side was found to correlate to several functional measures (dressing lower body and transfers at time 1, both dressing scores and wheelchair mobility at time 3), this ability did not change over time. Again, this most likely reflects the measure used, suggesting that a maximal lean to the paretic side is not a goal of therapy. It is surprising that the symmetrical sitting measure did not improve over time because this is frequently a reported goal of therapy, yet it showed minimal change in the present study. It may be that treatment is focused on teaching compensatory strategies that do not require maintenance of a symmetrical posture. This is supported by the lack of any significant relationship between the symmetrical measure and the FIM scores. Limitations of the Study The major limitation of our study was in our decision to use maximal leans, which are apparently not required for most functional movements nor incorporated into physical therapy treatment goals. Future study should be directed at the role of controlled partial leans in functional skill acquisition. In addition, the testing protocol required that the subjects place their feet flat on the floor during testing. This permitted subjects to stabilize themselves or push with their feet as the leans were performed. The contribution of foot pressure to the subjects' performance was not assessed but may have contributed to between- and within-subject variability. Future study might incorporate a measure of this foot-ground pressure as well as its contribution to the subjects' postural control. Further, the testing order remained constant for all subjects, which may be a confounding variable. An ordering effect was not expected because the subjects were tested under each condition 3 times, yet randomization would have eliminated this as a confounding variable. Nonetheless, the constant order allowed variation of the lean to the paretic and lean to the non-paretic sides. Finally, the use of the Balance System, which measures vertical force only, does not allow the generalization of these results to other forceplate systems that measure center of pressure; however, this system was chosen for the present study because it is a commercial unit that is presently being used in many clinical settings. Replication of this study with other available balance units is needed to further substantiate the findings. CONCLUSIONS This study is the first to attempt the evaluation of sitting balance by using the Balance System. Consistent results were obtained for both the nonpatient subjects and the subjects with hemiparesis, using the described protocol. Thus, this type of protocol may be effective in evaluating balance function in other patient populations. The exact protocol, however, may not be appropriate for documenting change over time. Only the measure for forward lean demonstrated a significant change over time. Thus, it may be more appropriate to attempt a controlled lean protocol, in which the individual is required to lean to a designated level, rather than the maximal lean protocol used in the present study. The FIM demonstrated a strong ability to document change over time in subjects with hemiparesis secondary to stroke. Thus, it appears to be an appropriate tool for the evaluation of individual patient progress or the relative effectiveness of a given treatment protocol. However, only a poor to moderate relationship was identified between the functional scores of the FIM and the postural control measures used in the present study. Therefore, the abilities measured in the postural control protocol (symmetrical sitting and maximal leans) are most likely not components of the functional tasks measured by the FIM. Again, a controlled lean protocol may more strongly correlate with functional skills such as dressing, transfers, and mobility. References 1. Tangeman PT, Banaitis D, Williams AK. Rehabilitation of chronic stroke patients: changes in functional performance. Arch Phys Med Rehabil 1990;71: Seitz RH, Allred KE, Backus ME, Hoffman JE. Functional changes during acute rehabilitation in patients with stroke. Phys Ther 1987; 67: Mohr JD. Management of the trunk in adult hemiplegia: the Bobath concept. In: Herdman S J, editor. Topics in neurology. Alexandria (VA): American Physical Therapy Association, Fisher B. 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