This post is part of our Stroke Series in which we share recent studies and perspectives on the use of motion analysis technology for the rehabilitation of stroke patients.
Survivors of strokes often suffer from instability and sway in posture. This is also common in elderly people due to neurological degeneration. Researchers from the University of Tokyo on Japan assessed the instability of post-stroke patients to further monitor and understand the postural control system. The study included subjects with hemiparesis due to stroke as well as elderly and young healthy subjects for comparison between age and pathology.
The subjects were asked to stand on a force platform and stand quietly for set time intervals. The force plate tracked the movement of the COM overtime, providing data on how a patient would sway during the trial. From the force plate data, COP, COM and COM acceleration were analyzed. A key metric, COP-COM was calculated, which is the distance between the COP and COM at any given time. While the COP and COM on their own cannot be definitively associated with instability, the COP-COM metric has been found to be affected by control system changes such as the effect of neurological impairment.
For the mediolateral axis (side-to-side) It was found that the COP-COM metrics and COM acceleration were of greater value in the post-stroke group compared to the healthy patients of both age groups, indicating that instability in the side-to-side direction is increased by stroke related impaired postural control. For the anteroposterior direction (front to back), the COP-COM and acceleration metrics were increased for both the post-stroke and healthy elderly group compared to the healthy young group. From these results, researchers concluded that instability in the front to back direction can be increased with age and not just the occurrence of a stroke. The results of this study provide further insight on the effects of a stroke on postural control, as it seems the stroke may affect stability side-to-side, while instability front to back is due to age and not pathology.
Researchers noted that the COP-COM calculation may be too complex to apply to a clinical assessment but had found that this metric was highly proportional to the COM acceleration. The results of this study demonstrate the potential for COM acceleration as an indirect and convenient method for the monitoring and assessment of postural control in patients. Furthermore, it is clear that the neurological damage from stroke has direction
Such analysis allows for further understanding of the outcome of strokes and can thus be used to improve the rehabilitation for post-stroke patients.
Force platforms similar to those used in this study are sold by BTS Bioengineering. Utilization of INFINI-T plates or integration of a PODIUM system enables the acquisition of COM and sway data in addition to the functional protocols designed for motion analysis.
This post was based on the following article, referenced:
Yu, E., Abe, M., Masani, K., Kawashima, N., Eto, F., Haga, N., et al. (2008). Evaluation of Postural Control in Quiet Standing Using Center of Mass Acceleration: Comparison Among the Young, the Elderly, and People With Stroke. Archives of Physical Medicine and Rehabilitation 89(6), p. 1139