1- What is it?
Posturography is a non-evasive technique that quantifies an individual's balance behavior in upright stance. As mentioned in previous articles (What is Balance?), balance is achieved and maintained by a complex set of sensorimotor control systems, which includes the visual, somatosensory and vestibular systems. It is through their integration in real time by the central nervous system that the body’s center of mass is maintained over its base of support.
Posturography is commonly divided into static and dynamic. Static is the study of the individual’s posture during unperturbed quiet erect posture, and dynamic during external perturbations usually by means of foam cushion or a movable surface. Most frequently, posturography techniques are used to objectively analyze the balance and postural response in different situations of increasing complexity, such as examinations with eyes open or closed, on firm or foam surfaces, with or without visual conflicts, among others conditions [1].
The PhysioSensing software (Figure 1) comes with the Body Sway protocol, a tool which allows the creation of a personalized posturography that measures several characteristics of postural control. This protocol allows selection of the following input parameters:
Visual system: eyes opened or closed;
Proprioceptive system: firm or foam surface;
Stance position: comfortable stance, two feet together, tandem, semi-tandem, stand on left or right leg;
Upper extremities: arms alongside body, hands on hips, arms crossed on chest or hands behind head;
Knee flexion angle: 0°, 30°, 60° or 90°;
Test time: values between 5 to 120 seconds;
Trials number: 1, 2, 3, 4 or 5 trials.
Figure 1 – (Left) Body Sway interface selection. (Right) Example of posturography examination with PhysioSensing solution.
2- What is measured?
The most common measure used in posturography is the center of pressure (COP). This is the location of the point of application of the ground reaction vector on the support’s surface. The ground reaction force corresponds to the sum of all the acting force on the plantar surface, representing all the muscle and gravitational forces acting at a period of time. Using technology like force and pressure plates (Figure 2), it is possible to quantify the small corrections that are performed to oppose the destabilizing effect of gravity, also known as body sway, during quiet standing. To find more about this take a look at this article.
Figure 2 – PhysioSensing force and pressure plate solutions.
The body sway can be translated into center of pressure values in the mediolateral (ML) and anteroposterior (AP) directions. There are two ways to visualize the COP data, through a statokinesigram graph (Figure 3), which represents the COP displacement in both directions during the posturography examination, and through stabilogram graphs (Figure 4), which shows the COP displacement over time for each direction.
Figure 3 – (Left) Illustration of mediolateral and anteroposterior displacements (left side), and representation of them in a statokinesigram (right side).
Figure 4 – Example of stabilograms for mediolateral (top) and anteroposterior (bottom) directions.
Several parameters can be derived from the statokinesigram and the stabilograms of the COP. Some examples of well-known parameters calculated in posturography are [2] (Figure 5):
COP Displacement or Length: total length of the center of pressure path. The COP path is the series of data points traced out by the movement of the COP.
AP and ML Range: Distance between maximum and minimum COP values in the anteroposterior and mediolateral direction (mm).
Mean COP Velocity: Distance travelled by center of pressure divided by test time (mm/s or °/s).
COP Ellipse Area: Area of the prediction ellipse with 95% of the COP values (mm²). It can be calculated with the principal component analysis method.
Figure 5 – (Left statokinesigram) Indication of AP and ML range, which correspond to the maximum and minimum values in the stabilograms. Illustration of COP data in detail (in the middle), in which each COP displacement (D1, D2, D3) can be observed. COP Length is the sum of all those displacements. Velocity can then be calculated by dividing each variation of displacement by the time interval between acquisitions. (Right statokinesigram) Representation of COP ellipse area with 95% of the COP values.
With PhysioSensing’s Body Sway protocol it is possible to obtain more than 30 parameters derived from COP data. Figure 6 shows an example of a clinical report of a posturography exam with four trials.
You may also like read about 12 Protocols for Balance Assessment with force/pressure plate.
Figure 6 – Example of Body Sway report with all the parameters obtained and graphs (statokinesigram, stabilograms and power spectral desnity from Fourier analysis).
3- Importance of posturography
Several conditions like stroke, Parkinson’s disease, multiple sclerosis, cerebral palsy, vestibular dysfunctions, knee and foot lesions, traumatic brain injury, among many others will affect balance. Thus, it is important to have tools such as posturography to help health professionals identify if there is a balance problem and the specific nature and/or the cause of the problem. The main value of a posturography exam is the objective information it provides, allowing to assess the patient [3]:
• Different sensory systems involved in balance (vestibular, visual and somatosensory);
• Changes of automatic and voluntary motor responses;
• Postural strategies;
• Deviations from the center of gravity;
• Changes of limits of stability.
For example, if a patient has difficulty in maintaining balance with eyes closes in unstable surface indicates a sensory pattern of vestibular dysfunction. There are also other patterns than can be found such as surface dependence or combined visual-vestibular deficit. Thus, posturography can help understand the pathophysiological mechanism in patients with balance disorders [4].
There are several studies about the use of posturography instruments in different pathologies. For example, Guntram et al. [5], studied the difference of body sway in elderly people and patients with Parkinson’s disease and detected significant differences of sway parameters in eyes closed examinations. Reid et al. [6] also used posturography to assess the incidence of large-fiber peripheral neuropathy by comparing the results with conventional electromyography (EMG) results. This study showed abnormal sway patterns only in patients who had EMG abnormalities consistent with the pathology, and differed significantly from the control subjects’ results. In Balaguer García R, et al. study [7], it was found that posturography with static and dynamic tests could discriminate between normal and peripheral vestibular disorder subjects, providing complementary information to classic tests like vestibulo-ocular reflex to better understand the functional status of patients with instability.
It is important to point out that it can also help health professionals to guide and evaluate the effectiveness and efficiency of rehabilitation programs to maximize treatment outcomes. As well as, establish baselines that are reproducible, practical and reliable, allowing monitoring of the patient's evolution.
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Bibliography
[1] J. E. Visser, M. G. Carpenter, H. van der Kooij, and B. R. Bloem, “The clinical utility of posturography,” Clin Neurophysiol, vol. 119, no. 11, pp. 2424–2436, Nov. 2008, doi: 10.1016/j.clinph.2008.07.220.
[2] M. Duarte and S. M. S. F. Freitas, “Revisão sobre posturografia baseada em plataforma de força para avaliação do equilíbrio,” Revista Brasileira de Fisioterapia, vol. 14, no. 3, pp. 183–192, Jun. 2010, doi: 10.1590/S1413-35552010000300003.
[3] C. Monteiro, Posturografia dinâmica computorizada. Vertigem do diagnóstico à Reabilitação, Edição José luis Reis., vol. I, Série II, Capítulo X. 2006.
[4] J. M. Furman, “Posturography: uses and limitations,” Baillieres Clin Neurol, vol. 3, no. 3, pp. 501–513, Nov. 1994.
[5] G. W. Ickenstein et al., “Static posturography in aging and Parkinson’s disease,” Front. Ag. Neurosci., vol. 4, 2012, doi: 10.3389/fnagi.2012.00020.
[6] V. A. Reid, H. Adbulhadi, K. R. Black, C. Kerrigan, and D. Cros, “Using Posturography to Detect Unsteadiness in 13 Patients with Peripheral Neuropathy: A Pilot Study,” Neurology & Clinical Neurophysiology, vol. 2002, no. 4, pp. 2–8, Sep. 2002, doi: 10.1162/153840902760213658.
[7] R. Balaguer García, S. Pitarch Corresa, J. M. Baydal Bertomeu, and M. M. Morales Suárez-Varela, “Static Posturography with Dynamic Tests. Usefulness of Biomechanical Parameters in Assessing Vestibular Patients,” Acta Otorrinolaringologica (English Edition), vol. 63, no. 5, pp. 332–338, Sep. 2012, doi: 10.1016/j.otoeng.2012.09.003.
Claudia Tonelo
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