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178
Statokinesigram
–5.2 cm
–2.0 cm
Ref.: centre of gravity position
Ref.: platform
43.5
D
S
A
I
26.1
3.7
–3.7
–26.1
–43.5
43.5
(mm)
26.1
3.7
–3.7
–26.1
–43.5
X mean
–5.9 mm
X mean
–50.0 mm
–2 s
–2 s
Stabilogram
a
b
Fig. 17.4 ( a , b ) Patient suffering from PPV after WI. The SKG with OC-HER ( a ) is abnormal;
the SBG ( b ) shows a prevalence of the oscillation on the anterior-posterior axis
P.L. Ghilardi et al.
179
Nevertheless, it must be considered that the fi ndings may be altered or modifi ed
because of the combined actions of more than one degree of lesion.
Beside a defi nition of the postural damage, static PG allows visualizing and
quantifying the extent of the disease and the effects of therapy on postural behaviour in patients with VSR defi ciency.
This observation has to be kept in mind in the case of patients suffering from postural
abnormalities following Wl in whom the posturographic test performed in EC-HER
plays an important role for evaluating the signifi cance of the cervical proprioceptive
input at the base of the vertiginous symptoms. In this framework, PG seems to be very
useful for monitoring both postural defi ciencies and the subsequent therapy.
Increased values of slow-sway component magnitude are evidenced in patients
with WAD despite of neck pain as assessed by Röijezon et al. [ 18 ].
In addition to the increase of postural sway that is more evident in anteroposterior direction (Ruhe A review), a recent work has evidenced that, during balance
tasks with closed eyes and one-legged stance, the relative mean activity of the anterior scalene, sternocleidomastoid, neck extensors and upper trapezius muscles,
expressed as mean relative activity related to maximum voluntary electromyography (%MVE) measured by surface electromyography, was signifi cantly increased
in WADs compared with healthy controls [ 19 ].
17.2 Tetra-ataxiametric Posturography
Tetrax system (Tetrax-IBS equipment by Sunlight Medical Ltd., Tel Aviv, Israel)
25–27 (CE patent n. 93741CE02; FDA establishment registration n. 3006701790)
consists of four independent mobile force plates, two for each foot. The plates are
positioned in order to measure any equilibrium disturbance from the two forefeet
and two heels. Each plate contains a strain-gauge force transducer, which is sensitive to vertical force. Tetrax provides independent output from the four balance
plates and, by taking the average of all four measurements, provides a description
of body sway in terms of displacement of the patient’s centre of pressure. Subjects
are requested to stand quietly on the platforms in a quiet room in four different conditions: eyes open and eyes closed on a solid surface and eyes open and eyes closed
on a foam pad in order to reduce somatosensorial and visual information [ 20 – 22 ].
The system measures the changes and fl uctuations of the vertical force exerted
by the corresponding heel or forefoot during the default 30-s experimental time and
emits four separate wave signals at a sampling rate of 34 Hz. On the basis of these
fl uctuations, the system computes a general stability score (ST), normalized for
body weight according to the following equation:
ST t n an an bn bn cn cn dn dn=−−+−−+−−+−−{[()()()( )]}
S
112 12 12 1212//WWN.
where a , b , c and d are the four pressure transducers, W is body weight, t is experi-
mental time and n is the number of signals sampled at 34 Hz.
Tetrax provides both quantitative and qualitative sway analysis.
17 Static Posturography and Whiplash
180
17.3 Quantitative Sway Analysis
General stability (ST) is, therefore, calculated as an index, which refers to a mean
of oscillations, recorded by each plate: the higher the value, the lower the stability.
It is the quotient of the sum of the amplitudinal changes (body sway), recorded in
microvolts and divided by body weight. While it is not a direct measurement of
postural stability, the fl uctuations of the vertical ground reaction force normalized
for body weight have been found to correlate with both the static and dynamic parts
of Berg’s balance test and with the anteroposterior centre of pressure (COP) velocity [ 28 ]. In fact, the ST score provides information about the adequacy of postural
adjustments. A lower ST indicates smaller fl uctuations and therefore better postural
control, and it has also been seen to be signifi cantly correlated to the equilibrium
score of the Equitest posturography system. The weight distribution index (WDI) is
calculated on the basis of the relative recorded weight at each of the four supports:
the higher the WDI, the higher the abnormal distribution of the weight that had to
be theoretically equally divided between the four supports.
17.4 Qualitative Sway Analysis
Fourier analysis of sway frequencies is a mathematical treatment of wave signals of
body oscillations on the horizontal plane produced by the patient in order to maintain an upright position.
The Tetrax system combines the signals from the left and right leg to result in
one sway frequency with a sampling rate of 34 Hz, as described by Kohen-Raz [ 23 ,
24 ]. The four signals recorded at the four sensors are analysed with the Fourier
transformation, and then Tetrax recalculates an average of the results obtained providing a unique parameter.
Fourier analysis is then carried out to determine which signal frequencies are
most common. Fourier analysis of sway frequency distribution shows that a normal
postural performance is characterized by a high intensity at the low range, and this
appears to indicate that posture is controlled with minimal effort, not involving any
activity of the semicircular canals, which are considered to be insensitive to body
displacements below 0.2 Hz.31 Fourier analysis of sway frequencies is divided into
eight frequency bands (F1–F8). Posturography with an interactive balance system
was recorded by means of equipment with four sensors; therefore, Fourier transformations were derived from four independent wave signals and were presented in the
form of a spectrum, broken down into the following eight frequency bands: F1
0.01–0.1, F2 0.1–0.25, F3 0.25–0.35, F4 0.35–0.50, F5 0.50–0.75, F6 0.75–1.00, F7
1.00–3.00 Hz and F8 above 3.0 Hz.
Previous studies on the Fourier spectral analysis of postural sway by Tetrax (25,
26, 30–33) have shown that typical ranges of postural frequency (i.e. frequency
bands) express the different levels of activity of postural subsystems, the systems
that affect postural sway. Study of postural frequency can provide insights into the
individual’s use of these postural subsystems, which include the vestibular,
P.L. Ghilardi et al.
181
somatosensory and other subsystems to maintain postural stability. Thus, spectral
analysis of postural sway might be a valuable tool in clinical diagnosis. Tetrax posturography has been shown to have a high test-retest reliability.
Dehner et al. [ 25 ] investigated the balance control in patients with acute QTF
grade II whiplash injuries of the cervical spine by means of Tetra-ataxiametric posturography in 40 patients with acute QTF grade II whiplash injuries and 40 healthy
matched controls. The stability index ST and the Fourier analysis FA (0.10–1.00 Hz)
were established for eight standing positions and sum scores were calculated. The
pain index was established using a visual analogue scale ranging from 0 to 100. A
follow-up examination was conducted for the patients after 2 months. The patients
with acute whiplash injuries of the cervical spine achieved signifi cantly poorer
results for both ST and FA than the healthy controls. There were no differences
between the eight standing positions for both ST and FA. After 2 months, 17 patients
had no change in the pain development, 21 patients showed an improvement in pain
intensity and two patients had deteriorated. The subgroup of patients with improvement in pain intensity showed a signifi cant improvement in balance control concerning the FA compared to patients with unchanged pain intensity. Authors
concluded that patients with acute whiplash injuries have a reduced balance control
as compared to matched controls. This study gives an indication that post-traumatic
neck pain is associated with impairments of postural control.
Kohen-Raz (unpublished data) coordinated a multi-country study in 90 chronic
WAD patients (Israel, Germany and Czech Republic) about Tetrax and WI. The
research was pointed to document backward displacement of COG following WI as
previously reported. Backward displacement is characterized, in Tetrax analysis, by
increasing of weight on the heels particularly evident during retrofl exion of the
head. Heel weight displacement is due to whiplash-induced disruption of head-totrunk coordination that is necessary to maintain stability of ground projection of
COG during head movements: in normals when the head moves backward, the
trunk and the pelvis moves forward in order to counteract head displacement, while
in WAD patients this kind of coordination is lost. WAD patients were compared to
90 healthy subjects from the same countries. A Student’s t -test confi rmed a signifi -
cant ( p < 0.05) weight displacement on the heels in WAD patients with respect to
normals in the three countries when patients retrofl exed their head.
17.5 Trunk Sway Measurement
In 2003 Allum et al. [ 26 ] proposed the use of body-worn sensors measuring angular
velocity (gyroscopes) or the acceleration of the trunk to effectively quantify balance
during stance and gait tasks to track improvements in postural control during recovery from an acute unilateral peripheral vestibular defi cit (UVL) and, successively, in
order to detect potential elderly fallers [ 27 ]. Postural control was quantifi ed using
simple measurements of trunk sway: amplitudes of trunk sway angle and angular
velocity, in the roll and pitch directions as well as task duration, were examined for
a battery of stance and gait tasks. Sjostrom et al. [ 28 ] used the same device in WAD
17 Static Posturography and Whiplash
182
patients. Trunk sway occurring during clinical stance and gait tasks was compared
between a group of subjects with a chronic whiplash injury, resulting from an automobile collision, and a normal collective. Twenty-fi ve subjects with history of
whiplash injury and 170 healthy age-matched control subjects participated in the
study. Trunk sway angular displacements in chronic whiplash patients were assessed
for a number of stance and gait tasks similar to those of the Tinetti and Clinical Test
of Sensory Interaction and Balance (CTSIB) protocols. Data analysis revealed several signifi cant differences between the two groups. A pattern could be identifi ed,
showing greater trunk sway for stance tasks and for complex gait tasks that required
task-specifi c gaze control such as walking up and down stairs. Trunk sway was less,
however, for simple gait tasks that demanded large head movements but no taskspecifi c gaze control, such as walking while rotating the head. They concluded that
subjects who have a chronic whiplash injury show a characteristic pattern of trunk
sway that is different from that of other patient groups with balance disorders.
Balance was most unstable during gait involving task-specifi c head movements
which possibly enhance a pathologic vestibulo-cervical interaction.
Vonk et al. [ 29 ] used trunk sway measured during several stance and gait tasks in
18 patients suspected of malingering in order to differentiate these from 20 patients
who had suffered unilateral vestibular loss 3 months earlier, 20 patients with documented whiplash injuries and 34 healthy controls. Classifi cation results ranged from
72 to 96 % and were equally accurate for task or criteria variables based on 90 %
sway values. The tasks yielding the best discrimination were standing with eyes
closed on a foam and fi rm surface, standing with eyes open on a fi rm surface, standing on one leg and walking tandem steps. The criteria yielding the best discrimination were standing with eyes open on a fi rm surface, the difference between standing
with eyes closed on foam and fi rm surfaces, the difference between walking tandem
steps and standing on one leg with eyes open and the difference between roll and
pitch velocity when walking eight tandem steps. We conclude that discriminating
suspected malingering balance disorder patients is possible using variables or criteria based on objective measures of trunk sway during several stance and gait tasks.
Findling et al. [ 30 ] showed a greater trunk sway for stance tasks and complex
gait tasks (e.g. walking up and down stairs) in patients with whiplash injury with
and without mild traumatic brain injury while they showed equal reductions in
trunk sway with respect to controls for simple gait tasks (e.g. walking while rotating
the head).
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P.L. Ghilardi et al.
185
D.C. Alpini et al. (eds.), Whiplash Injuries,
DOI 10.1007/978-88-470-5486-8_18, © Springer-Verlag Italia 2014
Different stable postures are possible according to the relative position of the three
principal muscle-joint systems – ankles, knees and hips – between the body’s COG
and the base of support (Fig. 18.1 ).
When external perturbations happen, the COG oscillates differently according to
the postural movement strategy adopted by each individual, depending on the
amplitude of the body’s displacement and on individual structural patterns.
The ankle strategy is most effective for small COG movements: the body acts
like a rigid mass and rotates about the ankle joints. This is possible by contracting
the ankle, thigh and lower trunk muscles.
The hip strategy, in contrast, is mostly used for large COG movements: the
body sways, moving the hips forward and backward with little ankle movement.
This generates horizontal reaction forces against the support surface opposite to
the direction of hip movement. The stepping strategy operates in order to avoid a
fall when the destabilizing force shifts the COG beyond the limits of stability
(Fig. 18.2 ) [ 1 , 2 ].
S. Barozzi • F. Di Berardino
Department of Clinical Sciences and Community Health,
University of Milan, Milan, Italy
Audiology Unit, IRCCS “Ca’ Granda” Ospedale Maggiore Policlinico, Milan, Italy
B. Monti
Private ENT Center “Otorinolaringoiatri Associati”,
Corso Stati Uniti 39, 10129 Turin, Italy
D. C. Alpini (
*)
ENT-Otoneurology Service, IRCCS “Don Carlo Gnocchi” Foundation,
Milan, Italy
e-mail: dalpini@dongnocchi.it
1 8
Dynamic Posturography
S. Barozzi, B. Monti, D. C. Alpini, and F. Di Berardino
186
Subject standing in
vertical position with
lower limbs in extension
Subject standing
with flexed knees
Subject standing on
hips with lower
limbs in extension
Fig. 18.1 Position of centre of gravity in different standing postures
Ankle
strategy
Hip
strategy
Fig. 18.2 Different strategies to
counteract displacements of COG
S. Barozzi et al.
187
18.1 Equitest: Description of the System
The Equitest system (NeuroCom International, Inc; Clackamas, Oregon) [ 3 , 4 ] is a
dynamic posturography device which allows different movements of the support
surface and different conditions of integration of sensory inputs (Fig. 18.3 ).
The Equitest system consists of:
• A platform provided with pressure-sensitive strain gauges located in each quad-
rant. It can translate horizontally forward or backward and rotate about an axis
colinear with the ankle joint.
• A movable visual surface which encloses the patient’s visual surrounding and
rotates about an axis colinear with the ankle joint.
• Computer, monitor and printer which analyse, visualize and print data. The
Equitest standard protocol consists of two tests: (1) the sensory organization test
(SOT) and (2) the motor control test (MCT).
Fig. 18.3 The Equitest system
18 Dynamic Posturography