Posturography
Posturography is the technique used to quantify postural control in upright stance in either static or dynamic conditions. Among them, Computerized dynamic posturography (CDP), also called test of balance (TOB), is a
Clinical applications for CDP were first described by L.M. Nashner in 1982, and the first commercially available testing system was developed in 1986, when NeuroCom International, Inc., launched the EquiTest system.
Working
Static posturography is carried out by placing the patient in a standing posture on a fixed instrumented platform (
Components of balance
Types of tests
The test protocols usually include a Sensory Organization Test (SOT), Limits of Stability Test (LOS), a Motor Control Test (MCT) and an Adaptation Test (ADT). The SOT test was developed by Nashner and is a computerized system that is made up of dual movable force plates and movable visual screen (EquiTest).[3] During the test the patient is instructed to stand still and quietly with eyes open or closed depending on which of the six tests is being administered. The patient performs multiple trials per test; a description of these tests can be found in the table below.[4] The SOT test is based on the fact that there are three sensory systems mainly involved in maintaining balance (vision, vestibular, and proprioceptive).[5][6] Minute spontaneous body sways are measured as well as reactions provoked by unexpected abrupt movements of the platform and the visual surroundings. Differences in these sways and reactions to system perturbations help to determine the patients ability to effectively use visual, vestibular, and proprioceptive input to maintain posture.[7] Wrisley et al. (2007) found that there are learning effects associated with the SOT test and therefore it could be used clinically to assess, improve and track changes in balance.
Condition | Vision | Surface | Visual Surround |
---|---|---|---|
1 | Eyes Open | Stable | Stable |
2 | Eyes Closed | Stable | Stable |
3 | Eyes Open | Stable | Sway-Referenced |
4 | Eyes Open | Sway-Referenced | Stable |
5 | Eyes Closed | Sway-Referenced | Stable |
6 | Eyes Open | Sway-Referenced | Sway-Referenced |
Condition | Patterns of abnormality on SOT analysis[8] | ||||||||
---|---|---|---|---|---|---|---|---|---|
Vestibular abnormalities | Multisensory abnormalitiesa | Extrasensory abnormalitiesb | |||||||
1 | Scores in 4, 5 and 6 are equal or better than in 1, 2, 3. | ||||||||
2 | |||||||||
3 | |||||||||
4 | |||||||||
5 | |||||||||
6 | |||||||||
Conclusions | Inability to make effective use of vestibular information | Inability to suppress the influence of inaccurate visual information ("visual preference") | Inability to make effective use of vestibular information AND to suppress the influence of inaccurate visual information | No effective use of either visual or vestibular information (dependence on somatosensory input for balance) | No effective use of either visual or vestibular information AND vision dependence | Dependence on visual and somatosensory inputs | |||
a Vestibular and extravestibular pathology
b Anxiety, simulation, exaggeration, etc. |
SOT results are subdivided in an Equilibrium Score, a Sensory Analysis, a Strategy Analysis and COG Alignment. The sensory analysis calculates 4 different scores: somatosensory (SOM), visual (VIS), vestibular (VEST) and visual preference (PREF) (otherwise known as "visual dependence",[9][10] an excessive reliance on visual information even when it is inappropriate). The scores are respectively calculated as ratios of the 6 different scores of the equilibrium score:[11]
MCT results include instead the Weight Symmetry, both for forward and for backward translations, Latency Scores for forward and backward translations, and Amplitude Scaling, which refers to the capacity of the participant to generate a response force adequate to the entity of the perturbation.
The limits of stability (LOS) is defined as the distance outside the base of support that can be traveled before a loss of balance occurs. The LOS test is frequently used to quantify this distance and has been suggested as a hybrid between static and dynamic balance assessment.[12] During this test the patient stands on the platform as directed above in the SOT test. The patient watches their movements on a screen so they can see each of the eight LOS targets. The patient begins with their COP directly in the center of the targets (displayed as a figure as a computerized person). At the onset of the test, the patient attempts to lean in the direction of the indicated perimeter target, without lifting their feet, and hold there until the test is complete.
According to necessity of the diagnostic workup, CDP can be combined with other techniques, such as electronystagmography (ENG) and electromyography.
The main indications for CDP are
See also
Sources
- Nashner LM et al. Adaptation to altered support and visual conditions during stance: patients with vestibular deficits. J Neurosci. 1982 May;2(5):536-44. Medline abstract
- Monsell EM, et al. Technology assessment: computerized dynamic platform posturography". Otolarynogol Head Neck Surg 1997, 117:394-398. Medline abstract
- Goebel, JA (Editor). Practical Management of the Dizzy Patient. Lippincott Williams & Wilkins Publ. 2000.
References
- ^ Hoffman, S.; Chaffin, M., Vertical ground reaction forces and center of pressure excursion during two-handed push exertions.
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- ^ Blaszcyk, J. W.; Lowe, D. L.; Hansen, P. D. (1994), Ranges of postural stability and their changes in the elderly, Gait and Posture, pp. 11–17