Abstract
Background Trunk control is thought to contribute to upper extremity (UE) function. However, this common assumption in neurorehabilitation has not been validated in clinical trials.
Objective The study objectives were to investigate the effect of providing external trunk support on trunk control and UE function and to examine the relationship between trunk control and UE function in people with chronic stroke and people who were healthy.
Design A cross-sectional study was conducted.
Methods Twenty-five people with chronic stroke and 34 people who were healthy and matched for age and sex were recruited. Trunk control was assessed with the Trunk Impairment Scale (TIS), and UE impairment and UE function were assessed with the UE subsection of the Fugl-Meyer Assessment (FMA-UE) and the Streamlined Wolf Motor Function Test (SWMFT), respectively. The TIS and SWMFT were evaluated, with and without external trunk support; the FMA-UE was evaluated without trunk support.
Results With trunk support, people with stroke showed improvement from 18 to 20 points on the TIS, a reduction in SWMFT performance times from 37.20 seconds to 35.37 seconds for the affected UE, and improvement from 3.3 points to 3.4 points on the SWMFT Functional Ability Scale for the function of the affected UE. With trunk support, the SWMFT performance time for people who were healthy was reduced from 1.61 seconds to 1.48 seconds for the dominant UE and from 1.71 seconds to 1.59 seconds for the nondominant UE. A significant moderate correlation was found between the TIS and the FMA-UE (r=.53) for people with stroke.
Limitations The limitations included a nonmasked assessor and a standardized height of the external trunk support.
Conclusions External trunk support improved trunk control in people with chronic stroke and had a statistically significant effect on UE function in both people with chronic stroke and people who were healthy. The findings suggest an association between trunk control and the UE when external trunk support was provided and support the hypothesis that lower trunk and lumbar stabilization provided by external support enables an improvement in the ability to use the UE for functional activities.
Stroke affects the control of the trunk muscles and, therefore, the ability to remain upright, adjust to weight shifts, and perform selective trunk movements to maintain stability during static and dynamic postural adjustments.1,2 The trunk is thought to play an integral role in postural stabilization by supporting controlled movement of the extremities during task performance.2,3 The development of trunk stability and control is considered to be a prerequisite to upper extremity (UE) function and use of the hand.4 It has been hypothesized that proximal stability allows for independent use of the arms and hands in manipulative and purposeful activity.4 However, this common assumption in neurorehabilitation has not been validated in clinical trials.
There is strong evidence that trunk control is an important predictor of overall functional outcome after stroke.5–9 The reported variance of functional recovery after stroke that is explained by trunk control ranges from 45%5,8 to 71%.10 Various studies5–10 have clearly illustrated that trunk control affects many facets of recovery in people with stroke, such as activities of daily living, balance, and gait. However, no research has built upon these findings to investigate the effect of trunk control on the recovery of UE function in people with stroke specifically, even though the UE plays a vital role in the performance of activities of daily living.11,12
Several studies on the use of trunk restraint in people with chronic stroke13–20 have demonstrated that stabilizing the trunk to restrict compensatory trunk movements leads to improved shoulder and elbow movements and thereby results in improvements in reaching to grasp. Our recent systematic review and meta-analysis revealed that trunk restraint has moderate effects in terms of the reduction of UE impairment, increased shoulder flexion, and the reduction of excessive anterior trunk movement during reaching in people with chronic stroke.21 Taken together, the findings suggest a possible relationship between trunk control and UE function. However, in previous studies,13,14,17,18 the trunk was restrained with a chest harness, which eliminated the need for trunk control.
Our aims were to investigate the effect of external trunk support on trunk control and UE function and to examine the relationship between trunk control and UE function in people with chronic stroke and people who were healthy. The trunk support that we used, unlike the trunk restraints used in other studies,13,14,17,18 provided stability to the trunk without restricting normal movement. We hypothesized that a more stable trunk enables improved dissociation of the UE from the trunk for function. Our findings could advance the understanding of how trunk control affects UE function in people with stroke and subsequently inform the design of targeted rehabilitation programs for the trunk and UE to optimize functional outcomes after stroke.
Method
Sample Size Calculation
Sample size was determined with a power calculation based on the between-group (people with stroke versus people who are healthy) difference in performance times on the Wolf Motor Function Test (WMFT), the primary UE function outcome measure. Mean WMFT scores have been recorded for people who are healthy (X̅=1.20 seconds, SD=0.20)22 and for people with chronic stroke (X̅=7.05 seconds, SD=6.85).23 To detect a difference of 5.85 seconds in WMFT performance times between groups and to achieve 85% power in a 2-sided test at a 5% significance level, we determined that 25 participants per group were required.
Participants
For this cross-sectional study, participants were recruited between November 2013 and March 2014 via paper and electronic advertisements and talks at 7 local stroke clubs. Participants were matched for age and sex. Inclusion criteria for participants with chronic stroke were as follows: 18 years of age or older, more than 6 months after stroke, able to understand the purpose of the study and follow simple instructions, and able to sit unsupported for 10 seconds. Exclusion criteria for participants with chronic stroke were as follows: brain stem or cerebellar stroke, presence of neurological or orthopedic pathology, and presence of acute low back pain. Inclusion criteria for people who were healthy were as follows: 18 years of age or older and able to understand the purpose of the study and follow simple instructions. Exclusion criteria for people who were healthy were as follows: history of neurological injury or disease, orthopedic spinal pathology, and orthopedic UE pathology. All participants provided written informed consent.
Outcome Measures
The Trunk Impairment Scale (TIS) was used to evaluate trunk control in the participants.1 The TIS consists of 3 subscales that assess static sitting balance, dynamic sitting balance, and trunk coordination on a scale ranging from 0 to 23 points. A higher score indicates better trunk control.
Upper extremity motor impairment after stroke was measured with the UE subsection of the Fugl-Meyer Assessment (FMA-UE).24 Each of the 33 items of the FMA-UE was rated on a 3-point scale. The maximum score is 66 points. Upper extremity motor function was measured with the Streamlined Wolf Motor Function Test (SWMFT).25 The 6 SWMFT tasks appropriate for people with chronic stroke were lifting the hand from a table to a box, lifting a can to the mouth, lifting a pencil with a 3-jaw chuck grasp, folding a towel, turning a key in a lock, and extending the elbow against a 0.45-kg (1-lb) weight.26 The performance time on the SWMFT tasks was measured with a stopwatch, and a 6-point Functional Ability Scale (FAS) was used to rate the quality of movement during the performance of the tasks.26 Good psychometric properties and good clinical utility that are appropriate for people with subacute and chronic stroke have been demonstrated for the TIS, FMA-UE, and SWMFT.27
Procedure
All assessments were conducted in the research laboratory of the University of Southampton, Southampton, United Kingdom. The participants sat unsupported on a height-adjustable plinth with their thighs fully supported on the plinth, knees at 90 degrees, and feet flat on the ground as the starting position. The assessment of UE impairment (with the FMA-UE) was conducted only for people with stroke. Trunk control was assessed with the TIS, once with no external trunk support and once with an adjustable high-density foam support around the trunk (Fig. 1). The use of an appropriately sized trunk support, which fit snugly at the posterior and lateral aspects of the trunk (up to the level between the tenth and twelfth thoracic vertebrae), provided trunk support but allowed free forward movement and minimal movement in the posterior and lateral directions.
Trunk support.
After the trunk assessment, the UE function of the participants was assessed with and without trunk support (with the SWMFT). People with stroke performed the SWMFT tasks with the unaffected UE and then with the affected UE. The order of testing with trunk support and without trunk support was randomized by use of blocked randomization,28 with a block size of 4, to avoid possible order bias due to practice or fatigue while ensuring equal numbers in the order protocols. People who were healthy performed the SWMFT tasks with the dominant UE and then with the nondominant UE. Hand dominance was determined with the Edinburgh Handedness Inventory–Short Form.29
Data Analysis
Data analysis was performed with IBM SPSS Statistics 20 software (IBM SPSS, Chicago, Illinois). The level of statistical significance was set at a P value of less than .05 for all tests. The Shapiro-Wilk test was used to confirm normal data distribution.
In view of the comparison of 2 groups (people with chronic stroke and people who were healthy) under 2 support conditions (with trunk support and without trunk support), a split-plot analysis of variance (SPANOVA) was used to analyze the results for the TIS and SWMFT performance times because they were interval variables. The affected UE of people with stroke was compared with the nondominant UE of people who were healthy. This design allowed participants with hemiparesis in the nondominant arm to be at less of a comparative disadvantage.30 The main effect of group, the main effect of support, and the interaction effect (interaction between group and support conditions) were analyzed. The results for the SWMFT FAS (ordinal scale) under the 2 support conditions were analyzed with the Wilcoxon signed rank test.
The SPANOVA was used to compare the difference in SWMFT performance times on the basis of sex, hand dominance, the order of testing of trunk support, the type of stroke, and the side of the affected UE for people with stroke and people who were healthy.
The association between the TIS and SWMFT performance times under the condition of no trunk support was determined with the Pearson correlation coefficient because the data were normally distributed. The Spearman rho (ρ) was used to determine the relationship between the TIS and the SWMFT FAS because the SWMFT FAS is an ordinal scale. Because of the normal distribution of FMA-UE data, the Pearson correlation coefficient was used to determine the relationship between the TIS and the FMA-UE.
Role of the Funding Source
This work was partly supported by the European Union under the Seventh Framework Programme, grant agreement #288692, StrokeBack. The funds were used to cover the transportation cost for the participants. Tan Tock Seng Hospital, Singapore, provided funding for the first author's PhD study at the University of Southampton, United Kingdom.
Results
Participants
Twenty-five people with chronic stroke (mean age=65.3 years, SD=12.0) and 34 people who were healthy and matched for age and sex (mean age=60.4 years, SD=12.4) were recruited (Tab. 1). There was no significant difference in age between people with stroke and people who were healthy. All of the participants were able to perform the SWMFT tasks.
Characteristics of Participantsa
Clinical Outcomes
People with stroke demonstrated significant improvement in TIS scores, from 18 points to 20 points (P<.001), significant improvement in SWMFT FAS scores, from a median of 3.3 points to 3.4 points (P<.01), and a significant reduction in SWMFT performance times, from 37.20 seconds to 35.37 seconds (P<.05), for the affected UE with trunk support relative to no trunk support (Tab. 2).
Clinical Outcomes of People Who Were Healthy and People With Strokea
With trunk support, the SWMFT performance times of people who were healthy was reduced significantly, from 1.61 to 1.48 seconds (P<.001) for the dominant UE and from 1.71 to 1.59 seconds (P<.001) for the nondominant UE (Tab. 2).
Comparison of Clinical Outcomes in People With Chronic Stroke and People Who Were Healthy
The results of the SPANOVA revealed a statistically significant difference (F1,57=44.39, P<.001) in TIS scores between people with stroke and people who were healthy, regardless of the support conditions (Tab. 3). The partial eta-squared (ηp2), a measure of effect size, was found to be 0.44 (large effect size). By convention, ηp2 values of 0.01, 0.06, and 0.14 represent small, moderate, and large effect sizes, respectively.31,32 People with stroke had significantly lower TIS scores (X̅=18.00 points) than people who were healthy (X̅=22.62 points). The difference between TIS scores with trunk support and TIS scores without trunk support, regardless of the groups, was significant (F1,57=33.06, P<.001), and the effect size was large (ηp2=0.37) (Tab. 3). Further analysis revealed a large significant interaction effect (between group and support conditions) (F1,57=20.60, P<.001, ηp2=0.27).
SPANOVA Results for TIS Scores and SWMFT Performance Time in People Who Were Healthy and People With Strokea
The results of the SPANOVA revealed a significant difference (F1,57=17.63, P<.001) in SWMFT performance times between people with stroke and people who were healthy, regardless of the support conditions (Tab. 3). The effect size was large (ηp2=0.24). The difference in SWMFT performance times between the 2 support conditions, regardless of the groups, was significant (F1,57=5.59, P<.05), and the effect size was moderate (ηp2=0.09). There was a moderate significant interaction effect (between group and support conditions) (F1,57=4.37, P<.05; ηp2=0.07). Although SWMFT performance times were significantly reduced with trunk support in both groups, the reduction was significantly larger in people with stroke (from 37.20 seconds to 35.37 seconds) than in people who were healthy (from 1.71 seconds to 1.59 seconds) (Fig. 2).
Moderate significant interaction effect between group and support conditions (P<.05, partial eta-squared=0.07). SWMFT-Time=Streamlined Wolf Motor Function Test performance time.
There was no significant difference in SWMFT performance times between people with stroke and people who were healthy on the basis of sex (F1,57=0.08, P=.78), hand dominance (F1,57=0.52, P=.48), or the order of testing of trunk support (F1,57=2.32, P=.14). For people with stroke, there was no significant difference in SWMFT performance times on the basis of the type of stroke (F1,23=0.95, P=.34) or the side of the affected UE (F1,23=0.07, P=.80).
Association Between TIS and Clinical Variables
There was no significant correlation between the TIS and SWMFT performance times (Pearson correlation coefficient r=−.31, P>.05) or between the TIS and the SWMFT FAS (Spearman ρ=.38, P>.05) in people with stroke and without trunk support. A significant moderate correlation was found between the TIS and the FMA-UE (r=.53, P<.01) in people with stroke and without trunk support.
No association was found between the TIS and SWMFT performance times in people who were healthy and did not receive trunk support (r=−.08, P>.05). The coefficient of correlation between the TIS and the SWMFT FAS in people who were healthy was not calculated because all achieved the maximum score of 5 on the SWMFT FAS.
Discussion
In the present study, we investigated the effect of providing external trunk support on trunk control and UE function and examined the relationship between trunk control and UE function in people with chronic stroke and people who were healthy by using clinical scales.
With trunk support, there were significant improvements in trunk control (TIS) in people with stroke and significant improvements in the performance of UE tasks (SWMFT performance times) and UE function (SWMFT FAS) in both people with stroke and people who were healthy. The significant reduction in the SWMFT performance time of 1.83 seconds with trunk support in people with chronic stroke was considered a clinically important difference. The minimal clinically important difference for WMFT time was reported to be 1.5 seconds to 2 seconds for people with chronic stroke.23 However, it is important to recognize that the SWMFT did not distinguish between tasks accomplished by UE movements and those accomplished by UE movements assisted by trunk movement because no kinematic analysis was conducted in the present study. We plan to conduct a kinematic analysis of the trunk and UE during performance of the SWMFT tasks to understand the mechanisms underlying the changes in outcome measures in a future study. A significant interaction effect (between group and support conditions) was demonstrated for the TIS and SWMFT performance times. The findings demonstrated that a higher TIS score was associated with better UE function and supported the common assumption that a stable trunk enables the dissociation of the UE from the trunk for function.
In the present study, we did not investigate the mechanisms associated with the improved UE function. However, we propose possible explanations for the significant reduction in SWMFT performance times and the improvement in SWMFT FAS scores when the trunk was supported. It is possible that a stabilized trunk enabled improved movement of the proximal and distal segments of the UE to occur against a background of stabilized core muscles of the body. This notion is supported by a study demonstrating a significant improvement in the functional reaching ability of the UE in people with stroke after an intervention consisting of trunk stability exercise.33 These data suggest that trunk stability has an effect on the stability of the shoulders which, in turn, improves the movement of the elbow, wrist, and fingers.34 A stable trunk provides a solid foundation for the torque generated by the extremities.35 Performing a reaching movement on a stable surface is different from the challenges faced when attempting to reach for objects while balancing on an unstable surface. Studies have demonstrated that unstable conditions can lead to decreased force output and muscle activation of the extremities.36,37
Previous trunk restraint studies13–21 demonstrated that the restriction of compensatory trunk movements by a physical restraint can lead to improved shoulder and elbow movements and thereby result in improvements in reaching to grasp. The present study demonstrated an improvement in UE function (SWMFT performance times and SWMFT FAS scores) with external trunk support that was not constraining. Taken together, the results indicate that stabilizing or physically restricting the trunk improves UE function. This effect may be explained by considering the concept of degrees of freedom (DOFs).
There are a minimum of 26 DOFs for UE movement38 and 3 DOFs each in the upper trunk and the lower trunk.39 In other words, the motor system has to manage at least 32 DOFs during a reaching task in an unsupported seated condition. Our external trunk support aided in the stabilization of the trunk, limiting trunk excursion or reducing the number of DOFs, especially in the lower trunk. This scenario could have led to a decrease in the overall demand on the motor system to reorganize the DOFs of the UE into a coordinated pattern of reaching movement and thus might have led to improvements in SWMFT performance times and SWMFT FAS scores. This notion is congruent with the finding, in a recent systematic review, that the manipulation of mechanical DOFs of the trunk via trunk restraint during reaching enhances the recovery of UE function after stroke.40
The improvements in SWMFT performance times and SWMFT FAS scores might have been due to the design (“C-shaped”) of the trunk support and its height (up to approximately the T10–T12 vertebral levels). The external support might have assisted the pelvis in tilting more anteriorly, thus facilitating a more extended position of the lower lumbar region. This alteration might have led to postural improvement for UE task performance. This postulation is supported by studies demonstrating that trunk posture and alignment affect UE performance.3,41 A neutral trunk posture and alignment significantly improved UE performance relative to flexed3,41 and laterally flexed3 trunk postures. Taken together, the findings of the present study and previous studies3,41 support the hypothesis that a stable trunk with good postural alignment enables the dissociation of the UE from the trunk for function.
No association was found between the TIS and SWMFT performance times or between the TIS and SWMFT FAS scores in people with stroke; this result may have been due to the relatively small sample size. However, the observation of an improvement in UE function with trunk support demonstrates a link between trunk control and UE, which is supported by a significant moderate correlation between trunk control and UE impairment (FMA-UE).
On the basis of our results, it can be suggested that incorporating external trunk support may offer an opportunity for better movement reeducation and facilitate better retraining of the UE. However, this concept must be explored further, and appropriately designed intervention studies are needed to examine the effect of providing external trunk support on UE function during rehabilitation after stroke.
The results of the present study must be considered in light of methodological limitations. All of the assessments with the TIS, FMA-UE, and SWMFT were administered by the principal investigator. This design may have introduced an element of observer bias to the study. Another potential limitation of the present study was the standardized height of the trunk support; the superior part of the trunk support was at different contact points on the posterior and lateral aspects of the trunk for the participants. However, the height of the trunk support was designed so that none of the participants would experience restrictions as they performed lateral flexion of the trunk during the TIS assessment. For addressing this limitation, however, trunk supports with different height dimensions could be created. We acknowledge that the use of external trunk support would invalidate the administration of the TIS. The reason for the inclusion of trunk support in the experimental procedure was to simulate the presence of someone with a “better” TIS score (ie, with better trunk control) in the same session and then to investigate its effect on UE function.
Another limitation that might have confounded the observed improvements in the outcome measures was the Hawthorne effect. To minimize any presence of the Hawthorne effect or performance bias, we did not inform the participants of the hypothesis of the study. Eliminating the Hawthorne effect completely in the present study would have been challenging because providing a sham condition would have been difficult, but this goal is an important consideration for future studies.
Because the present study was cross-sectional, a causal relationship cannot be drawn from the results unless future randomized controlled trials are conducted to verify the association reported here.42 In the present study, we measured trunk control not from a kinematic perspective but with a clinical scale based on the TIS. In a future study, we plan to capture kinematic data to shed light on the mechanisms associated with the improvements in UE function with external trunk support.
The observed improvements in trunk control and UE function with trunk support were immediate effects; carryover was not assessed because it was not the aim of the present study. It remains unknown whether a period of UE training with external trunk support for people with stroke will yield sustainable gains in the observed improvements in trunk control and UE function. In the future, we may conduct a randomized controlled trial to investigate the effectiveness of trunk support in improving UE function.
Future researchers may consider investigating the effect of trunk support on trunk control and UE in patients with trunk ataxia due to neurological disorders, such as cerebellar stroke or brain stem stroke. Gaining a deeper understanding of the mechanisms underlying trunk stability and trunk control may provide insights into a new therapeutic approach for the management of trunk ataxia and UE in neurorehabilitation.
External trunk support improved trunk control in people with chronic stroke and had a statistically significant effect on UE function in both people with chronic stroke and people who were healthy. The findings suggest an association between trunk control and UE when external trunk support was provided and support the hypothesis that lower trunk and lumbar stabilization provided by external support enables an improvement in the ability to use the UE for functional activities.
Footnotes
Mr Wee, Dr Hughes, Dr Warner, Dr Cranny, Dr Mazomenos, and Dr Burridge provided concept/idea/research design. Mr Wee, Dr Hughes, Dr Warner, and Dr Burridge provided writing. Mr Wee, Dr Warner, Mr Brown, Dr Cranny, and Dr Mazomenos provided data collection. Mr Wee and Dr Warner provided data analysis. Mr Wee and Dr Hughes provided project management and study participants. Mr Wee and Dr Burridge provided fund procurement. Mr Brown, Dr Warner, Dr Cranny, and Dr Mazomenos provided facilities/equipment. Mr Wee, Dr Hughes, Dr Warner, and Dr Burridge provided consultation.
The Institutional Review Board of the University of Southampton, United Kingdom, approved the study (Ethics Number 7547).
This work was partly supported by the European Union under the Seventh Framework Programme, grant agreement #288692, StrokeBack.
Mr Wee acknowledges Tan Tock Seng Hospital, Singapore, for funding his PhD study at the University of Southampton, United Kingdom.
- Received October 28, 2014.
- Accepted February 17, 2015.
- © 2015 American Physical Therapy Association
References
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