Effects of upper limb positions and weight support roles on quasi-static seated postural stability in individuals with spinal cord injury
Highlights
► Seated postural stability was quantified in individuals with spinal cord injury. ► Decreased seated postural stability was found in individuals with spinal cord injury. ► Distinct seated postural strategies were used by individuals with spinal cord injury. ► Upper-limb support increased seated stability in individuals with spinal cord injury.
Introduction
Individuals who sustained a spinal cord injury (SCI) experience sensorimotor impairments affecting the upper limbs (U/Ls), lower limbs and trunk. Consequently, the ability to efficiently perform daily activities in sitting that challenge balance and postural control may be altered in individuals with SCI [1]. These individuals need to develop new strategies to address the needs for stability and for trunk mobility while performing functional tasks.
Only a few studies have quantitatively investigated seated stability in individuals with SCI [2], [3], [7] or associated it with functional performance [4], [5] despite its relevance in clinical practice [6]. Shirado et al. [7] studied the long sitting position with and without hand support in individuals with SCI. The unsupported sitting position was found to be the most unstable position for individuals with SCI due to a longer displacement of center-of-pressure (COP) compared to healthy controls. Since the kinetic data were recorded using only one force plate underneath the buttocks and the kinematic data were studied only in the sagittal plane, the forces under the feet [8] and the change in the frontal plane were not accounted for. Moreover, the usual sitting position in a wheelchair or any other seat from which most functional activities are performed, is not with the legs extended but with them flexed (short sitting position), which influences pelvic and trunk position.
Interestingly, Chen et al. [9] compared sitting stability between individuals with complete high (T1–T6) and low (T7–T12) thoracic SCI during unsupported short sitting (quasi-static stability) and weight-shifts during leaning tasks (dynamic stability). Although participants with low thoracic SCI demonstrated better dynamic sitting stability than individuals with high thoracic SCI, no significant difference was revealed between the groups during the quasi-static position (potential ceiling effect). The lack of details regarding the level of the injury of the participants and the unequal number of participants in each group might have also biased the results. Additionally, no standardized U/Ls position across participants during the sitting position was described though the picture showed both U/Ls flexed at approximately 45° in the sagittal plane which may not be sufficient to challenge seated stability and discriminate across individuals with SCI. Once again, the ground reaction forces under the feet did not account for the displacement of the COP. Further studies investigating additional sitting positions and quantifying additional measures of postural stability are needed to further characterize seated stability in individuals with SCI.
The main objective of this study was to compare quasi-static postural stability between individuals with SCI and healthy controls during short-sitting positions performed using five distinct U/L positions and weight support roles. The secondary objective of this study was to evaluate the association between clinical variables and quasi-static seated postural stability measures. It was hypothesized that individuals with SCI would demonstrate reduced seated postural stability compared to healthy controls that would progressively worsen as the U/L positions reduced their ability to support their body weight. It was also anticipated that the severity of the sensorimotor impairments and the time since injury would be associated with the ability to maintain quasi-static seated postural stability among individuals with SCI.
Section snippets
Participants
Fourteen individuals with SCI and 14 gender-matched healthy controls (Table 1) participated in this study. Individuals were eligible to participate if they were able to independently maintain a short-sitting position with feet resting on the floor with no U/L support and had an activity tolerance of at least 60 min. None of the participants reported having a musculoskeletal impairment (other than the consequences of the SCI) or any other condition that might have altered their ability to
Results
Quasi-static COP measures are summarized in Table 2. Between-group differences for a given task and between-task comparisons for a given group are presented in Table 2, Table 3, respectively. The relationship between the seated postural stability measures and the clinical variables are revealed in Table 4.
Differences between groups
Individuals with SCI demonstrated lower stability performance and greater postural control demand compared to healthy controls, irrespective of U/L positions and weight support roles, which confirm the hypothesis that they exhibit reduced stability. The ML instability during supported sittings and the additional AP instability during unsupported sittings suggest the potential role of U/L support while compensating for anterior instability. These results corroborate the lateral COP pattern found
Conclusion
Individuals with SCI experienced reduced seated postural stability compared to healthy controls, regardless of U/L position or weight support roles. In individuals with SCI, bilateral U/L support provided the greatest seated postural stability. Unilateral hand support led to comparable stability performance despite increased control demand, which suggests additional fatigue and a limited ability to maintain this position for a long time. Unsupported sitting positions challenged seated postural
Conflict of interest statement
The authors declared no potential conflict of interest with respect to the authorship and/or publication of this article.
Acknowledgments
We thank all participants for their time and Philippe Gourdou, Pierre Desjardins, Michel Goyette for their technical assistance.
Cindy Gauthier received a Summer Research Award from the Quebec Rehabilitation Research Network. Dany Gagnon, Géraldine Jacquemin, Kei Masani and Milos Popovic are members of the Quebec-Ontario Spinal Cord Injury Mobility (SCI-MOB) Research Group funded by the Quebec Rehabilitation Research Network and the Ontario NeuroTrauma Foundation.
Dany Gagnon holds a Junior 1
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