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For correspondence:
Dr Giorgio Guidetti
Section of Clinical Otorhinolaryngology
Department of Neuropsychosensorial Pathology
Università degli Studi di Modena e Reggio Emilia
via del Pozzo 71
41100 - Modena
tel. 059-422777
e-mail: guidetti.g@policlinico.mo.it
ABSTRACT
We analyzed 150 subjects with an average age of 52,
differentiated on the basis of the otoneurologic examination, into:
normal (without alteration of the vestibular function: 28 cases ), peripheral
vestibular pathologies (with monolateral deficit in
labyrinth reflectivity in thermic tests: 73 cases), with central
pathology (22 cases ) and with mixed pathologies (27 cases ). All
subjects underwent a static posturographical test, both with closed and
open eyes, first standing directly on the platform, then with the support
of a cushion laid on the platform itself. The cushion used,
manufactured by the Ks company of Avellino with natural SMR (standard Malaysian
rubber), presents features which buffer, or at any rate
disturb, the foot's afferences, especially the proprioceptors. For
each test, surface and length of the body oscillations or sway were
measured, and the percentage of the interference of the foot support
factor on postural control was calculated with specific formulas. All
tests highlighted a marked difference between normal and pathologic
subjects. All subjects felt a strong destabilization during the tests
performed with the cushion, confirmed by a marked worsening of
postural performance in posturographic tests too, both with closed and
open eyes. The cushion employed in this study proved to be a valuable
tool for the assessment of footing interference on static postural
control. Its employment with closed eyes could be an effective
rehabilitation tool, especially in cases of monolateral vestibular
pathologies presenting compensation difficulties, to enhance the
activity of the healthy vestibular hemisystem, and in cases of
proprioceptive input impairment in other areas, to facilitate a
functional recovery with an increase in the relative compensatory
influence of vestibular information.
INTRODUCTION
Posture control and, more generally, the functioning of balance, are
guaranteed by a complex system that involves:
· Peripheral information from specific receptors (mainly labyrinth,
retinal and proprioceptors, but also acoustic and tactile ones)
· The elaboration of these information by the Central
Nervous System
· Reflex or voluntary motor output based on this information.
The pathologies of the vestibular component are those potentially more
destabilizing, but also the alteration of other input is able to
provoke disturbances to the posture and/or balance, although of minor
significance (7,8). The foot sole afferences are considered of primary
importance for the control of static posture (2,5). These are of two
types: exteroceptive and proprioceptive (3).
The cutaneous exteroreceptors, both capsulate (Ruffini, Pacini and
Meissner corpuscles) and non capsulate (Merkel cells and free nerve
endings) have got different features for adjustment and for
frequential sensitivity and
allow an evaluation of the time-space dynamic of cutaneous events,
providing information on the type of footing, the distribution of
forces and the speed of adjustment. The proprioceptors are also of
various types:
- Bound muscle ones indicate the length of the muscle (static response),
the speed of variation in length (dynamic response) and the state of
muscle contraction
- The tendonal organs of Golgi are considered mainly a recorder of
tendonal tension and therefore of muscle's contraction.
- The corpuscles of Vater-Pacini are receptors of vibrating stimuli,
especially of frequencies over 100 Hz, and whose role is still
little known
- Other corpuscles: these have not yet been well identified, but are
responsible for the perception of vibrating stimulus for frequencies
under 100 Hz.
- Articulation receptors are of various types and act as mechanical
receptors for either slow adjustments (extension receptors), that
signal the direction and speed of movement and the position of the articulation,
or else for fast adjustment, they are sensitive to acceleration. The
disturbance to the foot afferences involves the necessity of an adjusting
re-programming within the system, with a relative increase in the
interference of other peripheral input. In order to analyze such
interference clinically, various complementary posturographic tests
have been suggested (6,7) such as a vibratory muscular stimulation of
100 Hz (4,5), a controlled ischemia of the lower limbs (2) and of
footing on a soft surface (9), all of which are however not standardized
and often distressing for the patient.
We wanted to evaluate the degree of interference of the information
from the sole of the foot on static postural control, using a
technique welcomed by the patient, and with instruments easily to find
and of low cost.
INSTRUMENTS AND METHOD
We studied the interference of the inputs from the sole of the foot in
150 subjects, 59 male (39.3%) and 91 female (60.7%), of an average age
of 52 (minimum 18, maximum 85, s.d. 16.1 years)
On the basis of the initial otoneurological test, with
videonistagmographic and electronistagmographic recording, the
subjects were divided into :
· Normal (NORM), that is, without alteration of the vestibular
function: 28 cases (18.7%)
· peripheral vestibular pathologies (PER), that is with a monolateral
deficit of the labyrinth reflectivity in thermal testing: 73 cases
(48.7%)
· with central pathology (CENTR), that is with evidence of the
involvement of the Central Nervous System of different areas and type
and that anyway involves an alteration of the voluntary oculomotor
control (slow and saccadic eye movements) and/or of reflexes (NOC,
rotoacceleratory stimulation with and without visuo-vestibular
integration, calorie tests): 22 cases (14.7%)
· with mixed pathology (MIX), that is with both peripheral and
central pathology: 27 cases (18.0%).
All the subjects underwent then a static posturographic
routine test with the S.Ve.P. Amplifon platform, built and standardized
according to the norms of the French Association of Posturology (1).
The following tests were carried out in a Romberg position (that is in
an upright position, with arms by the sides and feet's points opened
wide apart of 30°), each
lasting 51.2 sec, with a frequency of 5 Hz:
· with open eyes (OE) standing directly on the platform
· with closed eyes (CE) directly on the platform
· with open eyes (OE) standing on the cushion set on the platform
· with closed eyes (CE) standing on the cushion set on the platform.
The following factors were also considered for every test:
· the surface (S) of oscillation or sway, expressed in mm,
represented by the confidence ellipse containing 90% of the sample
positions, indicating the precision of the system
· the length (L) of the oscillations, expressed in mm2 , represented by
the total distance from the center of pressure of the subject, which
indicates the energy spent.
The percentage of interference from the foot was evaluated both
with open eyes and with closed eyes, using the Podalic Interference Index (PII), both relative to the S (PIIS) and to the L (PIIL)
of the sway, calculated in the following way:
|
S with cushion |
| PIIS = -----------------------x 100 |
|
S without cushion |
 |
|
L with cushion |
| PIIL = -----------------------x 100 |
|
L without cushion |
The cushion used is square, sides 52 cm, height 5 cm. It is
manufactured by Ks of Avellino, in natural SMR (standard Malaysian
rubber). This is vulcanized 1,4 cis. poly-isoprene. The vulcanization causes a reversible elasticity, for the creation of transversal ties
between the matter chains which prevent sliding so that the position
is maintained. This rubber has the following physical properties:
1) E (elastic energy as by Hooke' s law applied to Young's module)
2) Coefficient of isothermal compression and deformation equal to and
corresponding to the elastic energy.
3) G (sliding module)
4) SIGMA (Poisson, module that represents the variation in the
possible length in relation to the initial length)
SIGMA = DELTA L / L = 0,5
__________________________ _ -2
5) Breaking point load = 300 Kg.cm
6) Extension to breaking point = 590%
These characteristics mean that the pressure put on the material is
expressed by rebound exactly as elastic force. This causes a buffer,
or marked disturbance, of the activity of tactile endings on the sole
of the foot and, above all, of proprioceptors, in particular of those
for rapid adjustment that need a directional vector and a depolarization
interval.
RESULTS
In all the tests done, a very significant difference was observed
between the NORM and the subjects with pathologies (PATH meaning PER,
CENTR and MIX) (table 1)
tab. I : surface (S) e length (L) of the postural oscillations and
value of p in the t-test, in the different conditions tested, in
normal subjects (NORM) and in those with a pathology (PATH).
The differences are more marked between the NORM and the MIX (table II).
Table II: surface (S) and length (L) of the postural oscillations in
the different conditions tested, in subjects with peripheral
vestibular (PER), central (CENTR) or mixed (MIX) pathologies.
All the subjects examined felt a marked sense of destabilization during the tests with the cushion, confirmed by a marked difference in
(t-test), both with open eyes and with closed eyes , between the values
of S and L with or without a cushion (table III).
Table III: Podalic index (PII) relative to the surface (S)
and to the length (L) of postural oscillation in the different
conditions tested, in all subjects examined.
There are no significant statistic differences between the FII of the
NORM and of the PATH, nor among the different types of PATH (table IV).
Table IV: Podalic interference index (PII) relative to the
surface (S) and to the length (L) of the postural oscillation in the
different conditions tested, in the various groups of subjects
examined.
The destabilizing interference of the cushion seems to be greater in
female subjects than in the male ones (table V).
Table V: Podalic interference index (PII) relative to the surface
(S) and to length (L) of the postural oscillation in the different
conditions tested: comparison (p relative to the t-test) with the
values obtained in male subjects (M) and female (F).
DISCUSSION
The computerized static posturographic test confirmed its reliability
as a method of study for postural control as long as it is used as a
standardized
system according to the international norms. In every test, a marked
difference between normal subjects and those with a pathology was
observed. The cushion used in this study proved to be an optimal means
for the evaluation of the interference of the sole of the foot on
static postural control. Although it obviously represents an element
capable of reducing the sensitivity of readings of body sway, its use
in fact allowed us to show that the interference of the sole of the
foot plays a large part in the static postural control, both in
normal subjects and in those suffering from a peripheral and/or central
vestibular pathology. The disturbance of this input, caused by the
characteristics of SMR rubber, provokes a marked worsening of both the
precision of the static postural system and of the energetic
expenditure called for by it, as much in the normal subjects as in
those with peripheral and/or central vestibular pathology.
CONCLUSION
The technique we used to disturb the information coming from the sole
of the foot proved to be effective, provoking a marked worsening of
the postural performance both in normal subjects and in those with a
peripheral and/or central vestibular pathology. This tells us on the
one hand that the input from the sole of the foot are of notable
importance for postural control itself and on the other hand, it
suggests that the natural rubber (SMR) cushion could be used for the
rehabilitation of balance problems. The patient standing upright on
this type of cushion and with closed eyes , is forced, in order to
maintain his postural control, to trust himself almost entirely to the
information coming from the labyrinth. This kind of rehabilitative
technique is therefore useful mainly in cases of monolateral
vestibular deficiency with a difficulty of compensation, in order to
favour the vicariant activity in the healthy vestibular hemi-system. A
logical use could be found at any rate in cases of alteration of the
input from proprioceptors of other areas, making easier a functional
re-programming where the influence of compensatory vestibular
information could be increased. Such experience in the future, in
particular with older subjects with multi-area pathologies, are
certainly foreseeable.
BIBLIOGRAPHY
1) Association Française de Posturologie: Normes 1985. AFP Edit.,
Paris, 1986
2) Association Française de posturologie: Huit leçons de
posturologie. AFP Edit., Paris, 1986
3) Brodal A.: Neuroanatomia clinica. Edi Ermes Edit., Milano 1983
4) Endom H., Magnusson M., Pyykko I., Schalen L.: Presentation of a
posturographic test with loading of the proprioceptive system. Acta
Otolaringol., suppl.455, 58-61 , 1988
5) Fusco M.A.: Testo atlante di posturologia plantare. Massimo
Marrapese Editore, Roma, 1998
6) Guidetti G.: Posturography in vestibular work-up of the patients. A
review. Acta ORL belgica, 46, 45-51, 1992
7) Guidetti G.: Diagnosi e terapia dei disturbi dell'equilibrio.
Marrapese Editore, Roma, 1996
8) Lackner J.R.: Some proprioceptive influences on the perceptual
representation of body shape and orientation. Brain, 111, 281-297,
1988
9) Norré M.E.: Posture in otoneurology., Acta ORL belgica, 44,
55-364, 1990 10) Pyykko I., Hansson G.A., Schalen L., Henriksson N.G.,
Wennmo C., Magnusson M.: Vibration-induces body sway. in: Claussen
C.F., Kirtane M. : Computer in der Neurootologie. 139-155,Verlag
Edit.Publ., Berlin, 1983
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