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Postural Alignment Is Altered in People With Chronic Stroke and Related to Motor and Functional Performance

Verheyden, Geert, PhD; Ruesen, Carolien, MSc; Gorissen, Monique, MSc; Brumby, Victoria, MSc; Moran, Rachel, MSc; Burnett, Malcolm, MSc; Ashburn, Ann, PhD

Journal of Neurologic Physical Therapy: October 2014 - Volume 38 - Issue 4 - p 239–245
doi: 10.1097/NPT.0000000000000054
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Background and Purpose: Trunk control is impaired after stroke but little is known about how changes in posture relate to other deficits. We examined spinal postural alignment in people with chronic stroke and explored the relationship between postural alignment and clinical measures.

Methods: Twenty-one subjects with stroke and 22 age-matched healthy comparison subjects participated in this observational, cross-sectional study. Data collection included measurements of thoracic, lumbar, sacral, and overall postural alignment in the sagittal plane in both sitting and standing. Measurements were made in different postures, including: upright, flexed forward, and extended backward. Clinical outcome measures included the Trunk Impairment Scale and its subscales, Fugl-Meyer Scale, Berg Balance Scale, Barthel Index, and Stroke Impact Scale.

Results: Significant deviations in postural alignment for participants with stroke compared with comparison subjects were apparent in sacral alignment (P < 0.02) and overall postural alignment (P < 0.01) in standing. These measurements were also significantly correlated with clinical outcome measures poststroke. Participants with stroke who had a more forward leaning posture when upright scored worse on the coordination subscale of the Trunk Impairment Scale (r = −0.61) and Berg Balance Scale (r = −0.64). Participants with greater anterior pelvic tilt when flexed forward and more overall inclination when flexed forward and extended backward scored better on the Trunk Impairment Scale, its subscales, and Berg Balance Scale (r = −0.6-0.7).

Discussion and Conclusions: People with chronic stroke have altered postural alignment in standing compared with subjects without neurological deficits. Investigating interventions focusing on increasing anterior and posterior pelvic tilt seem warranted.

Video Abstract available. See video (Supplemental Digital Content 1, http://links.lww.com/JNPT/A76) for more insights from the authors.

Department of Rehabilitation Sciences, KU Leuven, Leuven, Belgium (G.V., M.G.); Faculty of Health Sciences, University of Southampton, Southampton United Kingdom (G.V., C.R., V.B., R.M., M.B., A.A.); and Department of Rehabilitation, Radboud University Medical Centre, Nijmegen, the Netherlands (C.R.).

Correspondence: Geert Verheyden, PhD, Neuromotor Rehabilitation Research Group, Tervuursevest 101—Bus 1501, 3001 Leuven, Belgium (Geert.Verheyden@faber.kuleuven.be).

Part of this manuscript was presented at the European Stroke Conference held in Hamburg, Germany, in May 2011.

The authors declare no conflict of interest and no source of funding.

Supplemental digital content is available for this article. Direct URL citation appears in the printed text and is provided in the HTML and PDF versions of this article on the journal's Web site (www.jnpt.org).

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INTRODUCTION

People with stroke have impaired postural control; for example, in sitting, these individuals have more displacements of the center of pressure in both the anterior-posterior and medial-lateral directions.1,2 Studies have investigated this impairment in relation to functional ability, and several authors demonstrated that initial trunk performance, evaluated with the Trunk Impairment Scale (TIS), Trunk Control Test, or Postural Assessment Scale for Stroke, is an important prognostic factor for functional outcome after stroke.3–6 In our previous work,7 we already concluded that trunk control, clinically evaluated with the TIS and the Trunk Control Test, is still impaired in people with chronic stroke, and that this impairment was significantly related with measures of balance, gait, and functional ability.

Weakness of the trunk muscles or impairment of proprioception has been proposed as factors that may underlie the poor trunk control observed in people with stroke. Tanaka et al8 showed that there is a weakness of trunk flexion and extension muscles in participants with hemiplegia after stroke, and this might be a consequence of the insufficient use of high threshold motor units, disuse atrophy, and the fact that trunk muscles are bilaterally innervated. Karatas et al9 also found trunk muscle weakness and showed a correlation between this muscle weakness and the Berg Balance Scale (BBS) score at discharge from a rehabilitation program. Hacmon et al demonstrated that deficits in intersegmental trunk coordination during walking are related to clinical balance and gait function in chronic stroke.10 Another factor that might play a role is trunk position sense, assessed by measuring trunk repositioning error, and in a recent study,11 this was impaired in participants with chronic stroke and appeared to be related to clinical measures of balance and posture.

Beyond strength, coordination, and sensory function, the sagittal shape of the spine may also have implications for trunk control. Proper alignment of the spine is important for a good balance between external loads on the trunk and adequate trunk muscle function.12 Furthermore, the curvature of the lumbar and thoracic spine determines the length of the lever arm and, therefore, influences the function of the paraspinal muscles.13,14 In addition to the motor and sensory deficits that accompany stroke, many stroke survivors are positioned during the day in a wheelchair or in bed, wherein postural alignment may not be optimal. All these factors could contribute to differences in spinal alignment in people after stroke and in turn would influence pelvic positioning, which would further negatively impact postural alignment.

To the best of our knowledge, no previous study measured spinal curvature or alignment in participants after stroke and evaluated whether there is a relation between alterations in postural alignment and deficits in trunk, motor, and functional performance. Hence, the aim of the present study was to investigate whether there is a deficit in postural alignment in people with stroke and whether this is significantly related to trunk control, balance, upper and lower limb function, functional independence in activities of daily living, and participation. We hypothesized that people after stroke have an altered postural alignment, in both sitting and standing, in comparison with age-matched healthy comparison subjects, and more specifically a decreased lumbar lordosis and thus an increased posterior pelvic tilt. In addition, our hypothesis was that postural alignment alterations are related to motor and functional performance in people after stroke, especially clinical measures of trunk control.

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METHODS

Participants

Twenty-one people with stroke and 22 age-matched comparison subjects with no known neurological or orthopedic deficits participated in this observational, cross-sectional study. As this was an exploratory study, no previous data were available to calculate an accurate sample size. Participants were recruited from local stroke groups and a rehabilitation center in Hampshire, United Kingdom. Inclusion criteria were as follows: a diagnosis of stroke for more than 6 months, able to give informed consent, and able to sit and stand unsupported for 1 minute. Participants were asked to invite their partners to participate in the study as a control participant. Exclusion criteria for both groups were as follows: any acute episode of neck and back problems and other musculoskeletal, neurological, cognitive, or communication problems that would interfere with the protocol. Ethical approval for the study was granted by the University of Southampton (United Kingdom), Faculty of Health Sciences Ethics Committee.

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Procedure

At the beginning of the single assessment, an informed consent was signed, and demographic characteristics such as age, gender, and, for the participants with stroke, also time poststroke and affected side were documented. Postural alignment of all participants was measured using a hand-held, electromechanical measurement device (SpinalMouse, Idiag AG, Switzerland; for figures of the device, visit www.idiag.ch/en/products/spinalmouse/usage-applications) that has been shown to be a reliable and valid noninvasive, computer-assisted measurement of spinal alignment.15–18 We assessed alignment of the thoracic, lumbar, sacral spine, and overall postural alignment in both sitting and standing. During the measurement, no external support for balance was provided and subjects used no upper extremity support. We conducted measurements in the sagittal plane in neutral upright (starting), flexed forward, and extended backward positions. In each of the positions, the device was rolled once, hand-held on the paravertebral region from the spinous process C7 until S3, which had been previously identified by palpation and marked with a palpation pencil.

For the neutral upright standing position, participants were instructed to stand upright in a comfortable posture. For the upright flexed forward position, participants were asked to bend forward and bring the fingertips toward the floor without losing balance. For the upright extended backward position, participants were asked to cross both arms on the chest (participants with stroke holding the affected arm if necessary) and to lean backward with the trunk while looking forward and without losing balance. Once participants achieved the upright, flexed forward or extended backward position, they were asked to remain in this position and the measurement was conducted once. Subsequently, participants were allowed to relax. The same instructions were given for the sitting position. Instructions and posture demonstrations given to the participants were standardized for consistency by following predefined instructions read to each participant by the demonstrating researcher.

The alignment of individual sections of the spine (thoracic, lumbar, and sacral) as well as the overall (forward or backward) alignment of the spine (between T1 and S1) were calculated by the device. From the superficial shape of the spine detected by the measurement device, a recursive algorithm computes information concerning the relative position of the vertebral bodies between T1 and S3. A segmental localization (angle in comparison with the horizontal) of all vertebral bodies as the projection of their midpoints on the superficial contour of the back is obtained as final result. From the different individual angles obtained, total angles for the different sections of the measured spine are reported. Results in the sagittal plane are angles (in degrees) of thoracic alignment (kyphosis), lumbar alignment (lordosis), and sacral alignment (anterior or posterior pelvic tilt), with a fourth variable being the overall sagittal alignment (inclination) of the spine. A positive value indicates an angle toward kyphosis, anterior pelvic tilt, or forward inclination. A negative value indicates an angle toward lordosis, posterior pelvic tilt, or backward inclination. In both sitting and standing, a value of 0 indicates a neutral upright position.

Following the measurement of postural alignment, all participants with stroke were assessed with several clinical outcome measures to evaluate motor and functional ability. Trunk control and sitting balance were evaluated with the TIS, a reliable and valid clinical tool to measure motor impairment of the trunk.19 The TIS consists of 3 subscales; Static Sitting Balance evaluating static sitting, Dynamic Sitting Balance measuring lateral flexion initiated from the upper (shoulder girdle) and lower part (pelvic girdle) of the trunk, and Coordination evaluating rotation from the upper and lower part of the trunk. The Fugl-Meyer Scale (FM) was used to evaluate upper and lower limb function and has an excellent inter- and intrarater reliability and construct validity.20 To evaluate balance, we used the BBS, a standardized assessment of balance in participants with stroke, with strong psychometric properties.21 The Barthel Index was used to measure independence in basic activities of daily living. It is a widely used tool with good psychometric properties.22,23 Finally, the stroke participant group was asked to complete the Stroke Impact Scale, a self-report, reliable and valid outcome measure. It is a stroke-specific scale that measures not only physical disability such as hand function and mobility but also emotion, memory, and social participation.24 For all clinical measures used, a higher score indicates better performance.

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Data Analysis

Descriptive data analysis was performed for relevant variables. The Kolmogorov-Smirnov test was used to evaluate normality of data. In addition, we observed histograms to evaluate whether there was a normal distribution, and on the basis of this information, we used the independent t test (2-tailed) to investigate differences in all measured variables between people with stroke and comparison subjects. We used P < 0.05 as the level of significance for this exploratory study. To investigate whether there was a relation between postural alignment and functional ability in people after stroke, we calculated Spearman correlation coefficients between the alignment measures and ordinal clinical outcome measures for our participants with stroke. Correlation coefficients, wherein the relationship may be either positive or negative as indicated by “(−),” were interpreted as very weak (correlation between 0 and (−) 0.19); weak (between (−) 0.2 and (−) 0.39); moderate (between (−)0.40 and (−) 0.59); strong (between (−) 0.6 and (−) 0.79); and very strong (between (−) 0.8 and (−) 1).25 Statistical analyses were conducted using the statistical software program IBM SPSS Version 20.

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RESULTS

Participants

Demographical and clinical characteristics of both groups are shown in Table 1. There were no significant differences between the groups for gender (χ2 = 1.865; P = 0.172) or age (t = 0.44; P = 0.659). The mean time poststroke was 7 years (range: 1−28 years), meaning that we analyzed a chronic population. Participants had moderate to high scores for the clinical outcome measures shown in Table 1, indicating persistent deficits of motor and functional performance.

Table 1

Table 1

The measurements for people with stroke and comparison subjects in standing and sitting are shown in Tables 2 and 3, respectively. When measured in standing (Table 2), people after stroke in the upright position had a more forward leaning alignment than comparison subjects (mean, 5.43° vs 0.73°; P = 0.002). When measured in a forward flexed position, people after stroke showed less anterior pelvic tilt (mean, 59.48° vs 77.27°; P = 0.001) and were less forward inclined (mean, 85.71° vs 104.09°; P = 0.003) than comparison subjects. When measured in a backward extended position, people after stroke showed less posterior pelvic tilt (mean, 0.52° vs −10.23°; P = 0.014) and were less backward inclined (mean, −6.38° vs −18.68°; P = 0.000) than comparison subjects.

Table 2

Table 2

Table 3

Table 3

In sitting (Table 3), there was only a significant difference between groups in total inclination when measured in the upright and backward extended position. As with standing, people with stroke had a more forward leaning positioning in sitting in the upright position; a mean of 10.76° compared with 7.18° for comparison subjects (P = 0.041). People with stroke also had an average overall inclination of −3.19° backward compared with an average of −12.45° in comparison subjects in the backward extended position (P = 0.001). We found no significant differences in the thoracic and lumbar spinal region measurements between the 2 groups in either standing or sitting.

The correlation coefficients between measurements and the results of the clinical outcome measures are presented for the stroke group in Tables 4 and 5. In standing (Table 4), some variables showed significant correlations with clinical measures. Because of the exploratory nature of the study, we will focus on correlations from (−) 0.6 onward only.

Table 4

Table 4

Table 5

Table 5

In the upright position, the overall postural inclination was strongly, negatively correlated with the coordination subscale of the TIS (r = −0.61) and BBS (r = −0.64). Thus, people with a forward leaning posture when standing upright had a lower score on selective rotation of the trunk and functional balance. In the forward flexed position, we found strong, positive correlations between pelvic tilt and total TIS (r = 0.62) and the dynamic sitting balance and coordination subscales of the TIS (r = 0.70 and 0.73, respectively). This means that participants with stroke who had more anterior pelvic tilt when flexed forward had better trunk control and more selective movement capabilities toward lateral flexion and trunk rotation. A similar pattern was noted in the overall inclination in the forward flexed and backward extended position. Participants with stroke with more overall forward inclination in the flexed position scored better on the dynamic sitting balance subscale (selective lateral flexion) of the TIS (r = 0.65). People after stroke with more backward inclination in the upright position scored better on the coordination subscale (selective rotation) of the TIS (r = −0.64) and functional balance as measured by the BBS (r = −0.60).

In sitting (Table 5), there were less significant correlations found between the measured variables and the clinical measures, and no correlation was considered strong.

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DISCUSSION

We examined postural alignment in people with chronic stroke and hypothesized that postural alignment would be altered in people with stroke, in both sitting and standing, in comparison with healthy, age-matched comparison subjects; we anticipated a decreased lumbar lordosis and increased posterior pelvic tilt in participants with stroke. Furthermore, we hypothesized that alterations in postural alignment poststroke would be related to clinical measures of trunk, motor, and functional performance. Our results revealed significant differences in postural alignment between people with stroke and comparison subjects in measurements of pelvic tilt and overall spinal inclination in standing but not for degree of lumbar lordosis. In upright standing, participants with stroke had a more forward leaning posture. In the flexed forward and extended backward position, they showed less pelvic tilt and overall trunk inclination. These findings relate to a previous study by Messier et al,26 who suggested that the pelvis is more fixed after stroke and, therefore, there is less anterior tilt of the pelvis after trunk flexion. We are able to confirm this previous finding, and our study adds new knowledge by identifying a deficit in the backward, extension direction as well.

In participants with stroke, the altered pelvic tilt and overall inclination in standing was strongly correlated to several clinical outcome measures. Stroke participants with a more forward leaning posture in upright standing had significantly lower scores on trunk control and functional balance. According to Legaye and Duval-Beaupere,12 the sagittal posture assumed by the spine is important for a good balance between external loads on the trunk and adequate trunk muscle function. Thus, an altered sagittal posture could be linked to disrupted trunk muscle function. Overall, our results indicate that participants who were capable of more flexion and extension movement of the trunk, particularly the lower part of the trunk, had a better motor and functional performance, in both sitting and standing.

The relationship between poor balance, trunk control, and an altered pelvic tilt may indicate a postural control deficit within the core stability of people with chronic stroke. Pelvic control is important for trunk stability, and the lack of active muscle stabilization might lead to poor control of lumbopelvic position. The deep trunk muscles, in particular, have been shown to contribute to the stability of the lower spine,27,28 and as core stability requires the intrinsic control of musculature surrounding the sacral-pelvic region, our results may suggest that this control is lacking in the chronic phase after stroke and is reflected in postural control and movement deficits in our sample.

Contrary to our hypothesis, in sitting, there were less significant differences in postural alignment between people with stroke and comparison subjects. Also, there were fewer significant correlations found between measurements acquired in sitting and clinical outcome measures. This difference between the results in sitting and standing might be explained on one hand by the fact that sitting is more stable, therefore, there is less demand on trunk muscle function, and on the other hand by the fact that weakness of the lower extremity in people with stroke, when sitting, has significantly less influence on axial posture and postural control. Future research could examine more closely the relation between trunk control and lower limb activity.

We believe that our study showed that altered postural alignment was related to trunk control and functional balance. But in our opinion, this is only one component of a multifactorial problem. On the one hand, “peripheral” factors that might also play an important role are trunk muscle weakness and trunk position sense.8–11 On the other hand, “central” factors such as the perception of verticality might also contribute to postural control of the trunk.29 Furthermore, Spinazzola et al30 have suggested that postural instability of the trunk poststroke may be more strongly associated with right hemisphere lesions on the basis of the presence of a postural representational system in the right hemisphere. All these factors may contribute to adequate trunk function, and, therefore, it may be important to consider them when developing stroke rehabilitation programs to address deficits of postural control and balance.

From the clinical perspective, our results suggest that there may be value in physical therapy interventions that focus on improving lower trunk mobility in the chronic stage after stroke. The trunk is the central core of the body related to balance and mobility. Proximal control is required for distal mobility, balance, and functional activities. Training selective trunk muscles as part of a rehabilitation program for participants with stroke results in an improvement in trunk control and also has a carryover effect on balance and gait.31,32 In addition, it is well known that for a reaching task, the estimation of object location in the environment and the following reaching and grasping occurs with respect to the central reference frame of body posture.33 However, the question remains whether impaired reaching is caused by postural changes, by task (ie, grasp/reach) difficulties, or by impaired planning of the reaching trajectory. Future research could test these hypotheses, that is, studying reaching abilities during compensation of the altered pelvic posture and overall inclination in the sagittal plane. The present study has shown that especially pelvic tilt and overall spinal inclination is related to postural and functional performance. Increasing range of pelvic tilt may improve trunk control and as a result may lead to better trunk stability and balance or improvements in ability to perform upper limb activities.

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Limitations

A number of limitations warrant caution when interpreting our results. A relatively small sample size was used because of the fact that this was an exploratory study. A second limitation is that only 16 questionnaires of the Stroke Impact Scale were returned. This further limits the analysis of the impact of stroke on the participation in daily life. The wide range of number of years poststroke (1-28 years) is a third limitation. Narrowing this range or including more participants in different stages after stroke could give more detailed and clinically applicable information. Our participants were all approached via a rehabilitation center and local stroke clubs and, therefore, may not be representative for all people with chronic stroke. Another factor that limits the generalization of our results is that the participants who were not able to sit or stand unsupported for 1 minute were excluded from the study; this could have introduced an area of sampling bias as participants who were more severely impaired were excluded. Furthermore, due to time constraints, one measurement in each position was taken in order to allow us to evaluate a wide range of functional ability with clinical measures. Finally, our conclusions are based on the application of a noninvasive methodology for which only limited literature is available. Reliability and validity data for measurement devise are available, but no specific psychometric data exist for people with stroke. We see a clear need for further research concerning what exactly is measured with the electromechanical device used in this study, how segmental measurements are interrelated, and what the relation is between postural control and these measurements.

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CONCLUSIONS

Our results indicate that people after stroke, in comparison with age-matched comparison subjects, have altered sacral postural alignment and reduced overall inclination in the sagittal plane during standing. These alterations are present when standing upright as well as in a forward flexed and backward extended position. Our findings show that these alterations are strongly related to motor and functional performance poststroke.

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ACKNOWLEDGMENTS

The authors thank the Parkinson's UK Bath local branch that kindly donated the SpinalMouse equipment.

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Keywords:

balance; mobility; postural alignment; stroke

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