Proposal of standardization of Horus ® computerized posturography in adults Proposta de normatização da posturografia computadorizada Horus ® em adultos

1/8 Ferreira et al. CoDAS 2020;32(6):e20190118 DOI: 10.1590/2317-1782/20202019118 This is an Open Access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Study conducted at: Disciplina de Otorrinolaringologia, Cabeça e Pescoço, Faculdade de Ciências Médicas Universidade Estadual de Campinas – UNICAMP – Campinas (SP), Brasil. 1 Disciplina de Otorrinolaringologia, Cabeça e Pescoço, Faculdade de Ciências Médicas, Universidade Estadual de Campinas – UNICAMP – Campinas (SP), Brasil.


INTRODUCTION
The vestibular system is not the only source of sensorial information used to guide and maintain posture.Visual and somatosensory information, as well as the correct sensory integration originating in the brainstem, participate actively in maintaining body balance.This representation is compared with a map of prior knowledge of postural situations and efferences are then emitted for a postural adjustment (1) .Thus, the importance of a diagnostic method to evaluate these data individually becomes evident.This way, each system supplies diverse and equally important information.
Posturography complements the classic series of tests for diagnosis of vestibular impairment, which was redundant in the investigation of the vestibular ocular reflex (VOR) (2) .It is a complementary test for individuals presenting complaints related to body balance not diagnosed by conventional tests, such as electro-oculography with rotational and caloric testing and vestibular evoked myogenic potential (VEMP).Its clinical relevance consists primarily of diagnosing the presence of a disorder in body balance and, later, establishing if this disorder results from a problem in sensory input or integration, inefficient motor response, or a combination of both.It provides complementary information to the other tests, since it assesses, through different conditions, the participation of the visual, vestibular, and somatosensory systems in maintaining body balance.On the other hand, even patients who have posturography within normal limits may experience oculographic changes.Therefore, posturography is not a substitute for conventional vestibular tests, but it complements their findings and is prescribed in specific situations where investigation of the vestibulospinal reflexes (VSR) and sensory analysis of the balance disorder are relevant (3) .
Posturography analyzes the center of pressure (CoP) using a force platform.The CoP corresponds to the vertical projection of the center of body mass 2 .When a healthy individual remains erect and static on a force platform, small CoP oscillations are observed (4,5) .Quantification of these oscillations is essential to determine the parameters of normality (5) .
Anthropometric factors of each individual (weight and height), age, the position of the feet, and distance between the patient and the visual field can influence the CoP (4) .Elderly people present decreased proprioception and muscle strength, which directly affect balance and can increase the chance of falls (6) .The individual's 40 cm visual field is associated with better postural stability concerning the visual target positioned 3 meters away (4) .The closer the feet are, the smaller the area of the stability limit, and the greater the difficulty in standing upright (4) .Thus, it is vitally important to establish normality parameters considering these variations.
Therefore, this study aims to describe a proposal for standardizing the Horus® computerized posturography platform for adults without alterations in body balance, through descriptive analysis by age group and sex.

METHODS
This is a cross-sectional observational study approved by the Research Ethics Committee of Universidade Estadual de Campinas (number 78240017.0.0000.5404).All participants were informed about the procedure and signed the Informed Consent Form.The sample consisted of 61 adult individuals between 20 and 59 years old, with no complaints regarding body balance.All participants were submitted to the clinical evaluation protocol of the Otoneurology Sector of the Discipline of Otorhinolaryngology, Head and Neck of Universidade Estadual de Campinas, which includes anamnesis, ENT (Ear, Nose, and Throat) physical examination and cranial nerve exams, static and dynamic balance tests (Romberg and Fukuda respectively), coordination tests (diadochokinesis with alternate pronation and supination of the upper limbs and index-nose test), research for spontaneous and semi-spontaneous nystagmus, head impulse test, and head-shaking nystagmus.All participants were evaluated by the same team.The participants were chosen randomly among hospital staff, students, and passers-by in the previously set 12-month period between July 2017 and July 2018.The study included individuals without vestibular diseases and able to collaborate with the performance of posturography, which requires the integrity of vision and the ability to fix one's gaze at a predetermined point.Individuals with vestibular, neurological, or orthopedic diseases, using medication that could influence vestibular function, individuals who did not agree to sign the Informed Consent Form, or did not wish to participate in the study were excluded.Athletes, dancers or any individual potentially presenting balance performance well above average were also excluded.
Participants were submitted to six sensory conditions on the Horus® dynamic posturography platform (chart 1).This device, consisting of a force platform containing four sensors, arranged in a rectangular position at the four corners, was developed and is marketed in Brazil by Contronic (7) .It provides information from the center of pressure (CoP), mediolateral stabilogram, anteroposterior stabilogram, statokinesigram, and rehabilitation module, and is useful for diagnosis and vestibular rehabilitation.However, it still does not have known parameters of normality for the conditions tested.The stable surface corresponds to the platform surface itself, on which the patient stands barefoot and without support, and the unstable surface is tested using a medium-density pad.A 42-inch LED TV set was positioned 1 meter away from the patient's eyes, on the same horizontal plane of vision, following the manufacturer's orientation, with the projection of a fixed point and optokinetic tunnel to provide visual conflict.The stability limit area (SL) and 95% confidence ellipse area (CE), path length (PL), and average speed (AS) variables were analyzed.
Figure 1 shows the equipment and the way the test is carried out, always by two examiners to avoid the risk of falling.
The Horus® posturography platform is a static type, as it allows measuring the anteroposterior and lateral excursion of the body in individuals standing in an orthostatic position, stationary on a force platform.As the CNS uses a combination of sensory modes in maintaining posture and since the vestibular system responds more to changes in acceleration and orientation in space, posturography is believed to be a limited method for analysis of the spinal vestibular function (8,9) .However, it enables analysis of the patients' SL area -their ability to voluntarily move the center of mass with precision, speed, and velocity in all directions until their maximum body displacement limit is reached.Moreover, this posturography system allows dynamic tests to be performed by using a medium-density pad on the platform to simulate a proprioceptive conflict and simulates a visual conflict through visual stimulation using image projections on a widescreen.
Force platforms are currently indispensable in the study of balance and posture, especially for patients with dizziness complaints.Although there are several devices available in the market, the parameters analyzed are usually similar and equally useful for diagnosis and vestibular rehabilitation (VR) (10) .
The protocol employed by our service used configurations available in the platform software and others established by the service in particular, based on other protocols already described (11) .
Initially, the stability limit was marked.The participant was instructed to move their body in an anteroposterior and lateral direction using the ankle strategy, without moving their feet or trunk.The movement happened slowly until the individual reached his/her limit of stability, respecting the following sequence: forward and return to the starting position; to the right and return to the starting position; to the left and return to the starting position; backward and return to the starting position.Participants were instructed to perform the complete sequence of movements only once.If there was any movement of feet or torso, the test was restarted.After that, the six conditions were tested for 30 seconds each.Only one record of each condition was made, as allowed by the equipment.
The variables were also analyzed by age and sex and the equilibrium score (ES) and sensory integration test (SIT) were calculated for each condition and balance index (BI).The ES analysis considered that the goal in each of these conditions is the maintenance of static equilibrium.The participant was instructed to remain as stationary as possible on the platform, even in the face of cushion instability and visual conflict.Quantification of the results obtained ranged from 100% (no displacement recorded by the platform's sensors) to 0%, which corresponded to a fall in either direction.Based on the ES for each condition, the SIT was performed, consisting in the quantitative analysis of body equilibrium calculated using the ratio between the ES of two conflicting situations, to establish the most requested equilibrium functions in these situations, and the ES was found by the calculations described below: • somatosensory function: average of condition 2/average of condition 1 • visual function: average of condition 4/average of condition 1 • vestibular function: average of condition 5/average of condition 1 • visual dependency: average of condition 3 + 6/average of condition 2 + 5 • equilibrium index: arithmetic mean of conditions 1 to 6 In eyes-open conditions, there is the contribution of visual information.In situations where the cushion is used, proprioceptive information is distorted, requiring more from visual and vestibular information.When using the cushion with eyes closed, maintaining posture fundamentally depends on vestibular information (11) .The visual conflict with an optokinetic tunnel provides distorted, but not absent, visual information (12,13,14,15) .
The Horus® software generated reports containing information about the SL area, the 95% CE area, PL, and AS in the six sensory conditions.The 95% confidence ellipse area is defined as the 95% distribution area of the samples from the Center of Pressure.The length of the trajectory corresponds to the average displacement of the individual in the anteroposterior and laterolateral directions.The average oscillation speed is determined by the total distance divided by the 30 seconds of each test, according to information provided in the manufacturer's manual.
Posturography results were collected using data from the Center of Pressure by the balance platform for each stimulus, aiming to establish limits of normality for posturography parameters.Each parameter was analyzed both separately and jointly, to observe the performance of participants.
The descriptive analysis involved the presentation of frequency tables for categorical variables and position and dispersion measures for numerical variables.The Chi-square test was used for comparison of proportions.The Mann-Whitney test was used to compare measures between genders and age groups.The level of significance adopted for statistical tests was 5%.All confidence intervals constructed throughout the survey were defined with 95% statistical confidence.The SAS (Statistical Analysis System) System for Windows program, version 9.4 (SAS Institute Inc., 2002-2012, Cary, NC, USA.) was used for statistical analysis.

RESULTS
Sixty-one patients without vestibular complaints or changes in body equilibrium and chosen in the period set for the study were evaluated, 38 (62.3%) female and 23 (37.7%) male, 40 (65.57%) in the 20 to 40 years age group and 21 (34.43%) in the 41 to 59 years age group.The proportions of the groups by sex and age group were homogeneous, with a p-value of 0.1047 by the Chi-square test.
Tables 1 and 2 present anthropometric data.Table 3 describes the stability limit area discriminated by gender and age group.Table 4 shows the description of the CE, PL, and AS variables area for the six conditions tested.
Figure 2 describes possible normal values of the equilibrium score for the six conditions tested and the balance index, and figure 3 describes normal values of the sensory integration test.The minimum value would be the cutoff point between the healthy and the sick and can be useful for clinical analysis.The maximum value is not relevant for this analysis, as it represents an above-average performance.

Chart 1 .Figure 1 .
Figure 1.Schematic illustration of the functional diagram and positioning of the feet on the platform Source: User Manual -Horus -System for Posturography and Postural Rehabilitation.Pelotas: Contronic; 2016.

Captions: C1 -Condition 1 :
Eyes open with fixed target on firm surface.C2 -Condition 2: Eyes closed on firm surface (Romberg).C3 -Condition 3: Eyes open with visual conflict on a firm surface.C4 -Condition 4: Eyes open with a fixed target on an unstable surface.C5 -Condition 5: Eyes closed on an unstable surface.C6 -Condition 6: Eyes open with visual conflict on an unstable surface.

Figure 2 .
Figure 2. Normality values of the balance score for the tested conditions and balance index in both genders and age groups Caption: C1 -Condition 1: Eyes open with fixed target on firm surface.C2 -Condition 2: Eyes closed on firm surface (Romberg).C3 -Condition 3: Eyes open with visual conflict on a firm surface.C4 -Condition 4: Eyes open with a fixed target on an unstable surface.C5 -Condition 5: Eyes closed on an unstable surface.C6 -Condition 6: Eyes open with visual conflict on an unstable surface.

Figure 3 .
Figure 3. Normality values of the sensory integration test for both genders and both age groups

Table 2 .
Descriptive values of height and body mass by age group

Table 4 .
Descriptive values of the 95% confidence ellipse area (EC), the path length (CT) and the average speed (VM) of the Horus® conditions for both genders and age groups