Hemiparesis is the most frequent neurological impairment after stroke which balance abnormalities is the most frequent. Decreased muscle strength, range of movement, abnormal muscle tone, motor coordination, sensory organization, cognition, and multisensory integration can contribute to balance disturbances at different levels.
- Sensory Modalities and Integration
Somatosensory, visual and vestibular elements are sensory modalities and mainly involved in postural control integrated by the CNS.
In healthy people, these sensory modalities are required to maintain postural control with 70% somatosensory afferent, 20% vestibular afferent and 10% visual input. In a given situation, the nervous system gives one priority to one system over another to control balance in orthostatic position. Sensory reweighting is the ability to choose the appropriate sensory input (i.e in darkness, balance control depends of vestibular and somatosensory system).
In patient with stroke, balance impairments and decrease ankle proprioception are positively correlated and explained the increasing of falls. Additionally, abnormal interactions between three sensory modalities could explained abnormal postural reactions. Moreover, the vision impairment can provide an inappropriate and inaccurate information which can lead to compensatory responses over time. Therefore, sensory integration and sensory reweighting might be impairment.
- Biomechanical constraints
The most important biomechanical constraints is the quality and the size of the base of support. Thus, impairment of range of movement, tone, strength and muscle control as a result of stroke can influence the base of support, hence, postural control. It has been shown that more balance impairments a patient have and less low-limb strength he has. In addition, poor trunk control negatively influences balance.
- Movement strategies
The human body has sensori-motor postural strategies included hip, ankle and step strategies in order to maintain postural control. These strategies involve muscles synergies, movement patterns, joint torques and contact forces. Balance control can be reactive or anticipatory and this depends of the CNS to predict and detect instabilities in order to active strategies. Delays in postural responses may be caused by a slow increase in muscle activity or changes in spatiotemporal coordination of synergies. Patient with stroke have strategies not often efficient for stability, hence, increasing risk of falls.
- Cognitive processing
Greater attentional demands can be required from patients with stroke in tasks of static postural control, particularly as task difficulty increases. Inadequate allocation of attention can lead to a greater falls risk.
- Perception of verticality
Adequate perception of verticality is important for postural control. Nondisabled persons are able to identify gravitational verticality within 0.5° without using visual feed- back. Postural perception of verticality can be abnormal in a stroke patient in presence of a visuospatial neglect. Additionally, pusher syndrome (resistance to support weight on non-paretic side, so, fear of falling toward the non-affected side) has a perception of body posture altered but interestingly, the visual and vestibular inputs are not disturbed in order to determine the vertical.
- Stroke test/ scale
Previous studies and clinical placements have involved exposure to a number of the tests typically associated with stroke patients. The International Classification of Functioning (ICF) has the advantage to be international and understandable anywhere. I use this one in order to provide a global view of the study case. I observed the Berg Balance Scale as involved to test a number of static, dynamic and functional tasks of daily routine specifically for stroke population. I watched the Time Get Up and Go test which provide aspects of balance in frail elderly population with cognitive impairment. I research about the Functional Reach Test and the link with dynamic stability but I never used. Indeed, I think better scale exits to test this component like 4 Meter Walk test or Time Get Up and Go test. I employ the Falls Risks Assessment Tool involved to assess risks fall and find the best strategies for the study case. I make use of Short Physical Performance Battery as a scale more for elderly people and stroke people on order to provide an idea of disability of the study case involved balance tests, chair stand and gait speed. I used also Barthel Index in order to provide an assessment about patient daily routine.
Jehanne Crouzier 