The relationship between sitting stability and functional performance in patients with paraplegia

Objectives: To compare sitting stability between patients with high and low thoracic spinal cord injury (SCI), to determine the factors that can predict sitting stability, and to examine the relationship between sitting stability and functional performance. Design: Cross-sectional assessment was performed on subjects with paraplegia. Setting: Rehabilitation hospital affiliated with a medical university. Participants: Convenience sample of 30 adults with complete chronic thoracic SCI. Interventions: Not applicable. Main Outcome Measures: (1) Postural sway during quiet sitting over 30 seconds was recorded as static sitting stability, and composite maximal weight-shift during leaning tasks over 30 seconds was measured as dynamic sitting stability; (2) age, body weight, trunk length, trunk strength, postonset duration, injury level, and presence of spasticity were examined as predictive variables for sitting stability; and (3) the time for completion of upper- and lower-body dressing and undressing and transfer was measured as functional performance. Results: A significant difference in composite maximal weight-shift was found between high and low thoracic SCI subjects (t=2.90, P<.01). Injury level and trunk length were 2 important predictive factors for dynamic sitting stability, and they explained 43.5% of the variance. Only the completion time of upper-body dressing and undressing correlated significantly with static (r=.465, P=.01) and dynamic (r=-.377, P<.05) sitting stability. Conclusions: The subjects with low thoracic SCI showed better dynamic sitting stability than those with high thoracic SCI. Injury level and trunk length, not trunk flexion or extension strength, predicted the outcome of dynamic sitting stability. Measures were not precise enough to predict functional performance from the viewpoint of injury level and sitting stability. The underlying premise that a reduction or increase in trunk strength is indicative of poorer or better sitting stability in SCI individuals is questioned, and implications for problem identification and treatment planning are discussed.