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188
18.1.1 Sensory Organization Test
The SOT assesses the ability of a subject to use visual, vestibular or somatosensory
information to maintain upright stance under different sensory conditions [ 5 , 6 ]. Tests
conditions are meant to isolate the function of each equilibrium subsystem by reducing the contribution of others or by presenting confl icting sensory inputs. Thus, during
the test, the platform and the visual surrounding are fi xed or rotated proportionally to
any forward or backward sway of the subject (sway-referenced support and swayreferenced visual surrounding) according to the following six combinations (Fig. 18.4 ):
1. Normal vision (fi xed support)
2. Absent vision (fi xed support)
3. Sway-referenced vision (fi xed support)
Fig. 18.4 The sensory
organization test
S. Barozzi et al.
189
4. Normal vision (sway-referenced support)
5. Absent vision (sway-referenced support)
6. Sway-referenced vision (sway-referenced support)
Information from a sense subjected to sway referencing suggests that the
orientation of the body’s COG relative to gravity is not changing when in fact it is.
Normally, individuals ignore a sway-referenced sensory input and maintain balance
by using other sensory inputs.
In addition to sway referencing, eyes-closed conditions are used to further isolate
the somatosensory and vestibular systems. The original test scheme does not reduce
or confound the contribution of the vestibular system. Head extension may also be
useful because it places the utricular otolith organs in a disadvantageous position
[
7 , 8 ]. Head extension also enhances cervical proprioceptive input; therefore, it could
be favourably employed in testing balance of whiplash-injured patients. To highlight
the importance of dynamic posturography to detect clinical equilibrium disturbances,
Fitzpatrick et al. [ 9 ] in a study on perturbed stance, showed that feedback control
alone does not allow stable balancing with large disturbances. In the same way, Horak
et al. [ 10 ] in 2002 observed that disturbance compensation, which is incomplete (only
partial) with small disturbances, increases with increasing stimulus magnitude.
A computerized system evaluates COG sways and calculates, for each test, the
equilibrium score, comparing the patient’s maximum anterior to posterior COG
displacement to the theoretical maximum displacement of 12.5°.
The Equitest analysis programme also calculates:
• The composite score, the average of all conditions’ scores (Fig. 18.5 )
• Sensory analysis, which allows identifi cation of a sensory dysfunction and/or an
abnormal sensory preference by calculating the ratios of different sensory
conditions (Fig. 18.6 )
Equilibrium score
Sensory conditions
Composite
Fall
NN NN
SS SS
100
75
50
25
123456
84
Fig. 18.5 The composite score
18 Dynamic Posturography
190
• The strategy of movement adopted to maintain upright stance (ankle strategy, hip
strategy) (Fig. 18.7 )
• The COG alignment (Fig. 18.8 )
Sensory analysis
Fall
Hlp 25 50 75 An
k
Ankle dominat
Hip dominat
100
75
50
25
Fig. 18.7 The strategy
analysis (ankle dominant)
100
75
50
25
SOM
VIS
VEST PREF
Sensory analysis
0
Fig. 18.6 The sensory
analysis
S. Barozzi et al.
191
18.1.2 Motor Control Test
The MCT studies automatic postural responses to unexpected movements of the
base of support: small, medium and large backward translations; small, medium and
large forward translations. Each trial is analysed in terms of latency, amplitude and
symmetry of response. When the support surface is unexpectedly translated forward
or backward, the body initially remains stationary and becomes offset relative to the
base of support. The stiffness of ankle joints initially resists to the sway but is
insuffi cient to stabilize the COG sway.
In backward translations, when the ankle strategy is used to counteract the
forward displacement, a sequential activation of distal to proximal extensor muscles
is adopted (gastrocnemius, hamstrings, paraspinal muscles). These muscle
activations help to stabilize knee and hip joints so that the body moves as a coordinated unit about the ankle joint [ 11 ].
When the hip strategy is used, we observe an activation of the fl exor
muscles of the hip joint (quadriceps and abdominals) that moves the body
backward [ 12 ].
In forward translations, when the ankle strategy is used, we assist with a
sequential activation of distal to proximal fl exor muscles (tibialis anterior, quadriceps and abdominals).
In the hip strategy, the hip joint moves forward to activate paraspinal muscles and
hamstrings. In the MCT the platform is also tilted abruptly up and down to evaluate
adaptation to disruptive balance forces [ 13 ].
COG alignment
Fig. 18.8 The COG
alignment
18 Dynamic Posturography
192
Toes-up rotations of the support surface stimulate proprioceptors in the gastrocnemius muscles of both legs and elicit muscle forces which tend to destabilize posture [ 14 , 15 ]. The adaptation test assesses the patient’s ability to ignore these
disruptive somatosensory inputs within fi ve trials (Fig. 18.9 ).
4
4
2
4
200
150
100
50
200
160
120
80
200
160
120
80
0
200
150
100
50
0
25
20
15
10
5
0
25
20
15
10
5
0
SML
M
Amplitude scaling Amplitude scaling
Adaptation – Toes Down
Adaptation – Toes UP
L
24 44
ML
ML
Left Right
Left Right
Left
Patient: P.
Referred by:
Sway–Referenced Gain: 1.00
Age:
ID:
Right
Left
Right
∗ = Left
∗
∗
∗
∗
∗
= Right
ML
1000
Operator ID:
File: 930107A.EQ
T
Date: 01 Mar 1993
Time: 10:11
Latency (msec)
Forward translations
Latency (msec)
Backward translations
Weight symmetry
Backward translations
Weight symmetry
Forward translations
SML
S
M
L
S
M
L
200
1000 200
123 4 5
123 4 5
Fig. 18.9 The motor control test
S. Barozzi et al.
193
18.2 Dynamic Posturography in Whiplash Injuries
The Equitest is a modern device which provides an objective assessment of
balance function in its entirety. With the composite score we have an individual
global equilibrium measure which can be compared to the average score of clinically normal individuals of the same age.
Several studies made in the normal population confi rmed the confi dence and the
repeatability of computerized dynamic posturography results.
Many patients with “whiplash syndrome” experience unrelenting neck stiffness
and pain. This abnormal muscular tension is postulated to be causally related to a
central disorder of postural control, which has evolved secondary to injury of the
inner ear labyrinthine structures.
Moving platform posturography was used by Chester [ 16 ] to demonstrate the
presence or absence of a static or dynamic equilibrium disorder in 48 patients who
had experienced the oscillation forces induced by a rear-end automobile collision.
Other vestibular tests were used to document dysfunction of the semicircular canals
and the otolith structures. A high percentage of patients were found to have faulty
inner ear functioning, leading to ineffi cient muscular control of balance and erect
posture. Active perilymph fi stulas were identifi ed at surgery in seven patients.
Kogler et al. [ 17 ] investigated a total of 32 healthy subjects (16 men, 16 women,
age range 21–58 years), and ten patients age range 27–62 years (mean 44 years)
with neck problems and associated balance problems since a whiplash injury were
tested for postural control using the Equitest. The normal subjects were initially
split into four-age groups in order to estimate the effects of age on performance.
The postural stability was evaluated for dependence of support surface conditions
(stable or sway-referenced), visual input (eyes open or closed) and head position
(neutral, left rotated, right rotated, extended backwards or fl exed forward). As
expected, visual cues as well as stable support surface improve postural stability
( p < 0.001). Postural stability is statistically different in the head-extended- backward
condition compared with the other four head positions ( p < 0.001 in all cases) in
both patients and controls. Eliminating this test condition from the analysis, only a
slight ( p < 0.05) difference between head forwards and head turned left remained.
This pattern of results remained if the normal subjects were only split into two age
groups instead of four. Finally, the patient group exhibited signifi cantly lower postural performance than all the groups of normal subjects ( p < 0.01), but none of the
normal groups differed signifi cantly from each other. It is concluded that the postural control system is signifi cantly challenged in the head-extended-backward condition in both normal subjects and patients with previous whiplash injury and
persistent neck problems. The patient group differed statistically from all groups of
normal subjects. This suggests that neck problems impair postural control and that
the head-extended position is a more challenging task for the postural system to
adapt to.
Our experience in evaluating whiplash injuries has showed that in the SOT the
composite score can separate, in a confi dent manner, normal subjects at a conventional neurotologic evaluation from pathological ones. The only discordance was
given by benign positional vertigo results which can be normal at SOT.
18 Dynamic Posturography
194
The opportunity to have available, objective and repeatable data is important in
medical-legal cases following whiplash injuries [ 18 ].
For this purpose computerized dynamic posturography can detect patients
who exaggerate symptoms of unsteadiness when test results are physiologically
inconsistent. In our experience, in case of deliberate exaggeration of symptoms, we
found one or more of the following inconsistent patterns:
1. Composite scores lower than 42 % in subjects who do not have ataxia and
ambulate without the use of balance aids.
2. Better performances under more diffi cult conditions (4–5–6) then under easier
ones (1–2–3).
3. Declining performances during successive trials, with a percentage of equilib-
rium in the fi rst trial at least two standard deviations greater than the third.
4. Sinusoidal sway traces of COG.
5. Dispersion of the x–y plots of the initial COG alignment.
6. Sudden falls after periods of relative stability in the SOT.
7. Abnormal adaptation in toes-up and toes-down rotation. In our experience,
the 70 % of patients with cervical distortional trauma and with an abnormal
composite score and consistent test show vestibular dysfunction patterns on SOT
sensory analysis (the sensory ratio of conditions 5/1 is abnormal).
With somatosensory and visual inputs misleading and unavailable, such as in
condition 5, the upright position is allowed by otolith vestibular function which
controls the extensor antigravity muscles. Therefore, vestibular inputs assessed by
sensory analysis are prevalently from the otolith rather than from the canal organs.
For this reason in patients with peripheral vestibular disorders, Equitest results do
not always agree with caloric tests.
So, the abnormal vestibular function found in most patients with cervical trauma
can be explained by a defi cit in the extensor antigravity muscles [ 19 ].
The motor control strategy most commonly observed in sequences of whiplash
injuries is the ankle strategy. This is evident in the strategy analysis where points
fall along a nearly vertical line on the right of the plot. This fi nding means that
patients are abnormally dependent on ankle movements even when the amplitude of
sway approaches the limits of stability.
In patients who underwent whiplash injuries, trauma directed to the cervical
spine usually reverberates along the whole column causing a hypofunction of the
erector muscles and a prevalence of the fl exors which moves forward the body’s COG.
In order to resist the tendency of falling forward and to move the COG inside the
base of support, some corrective postural arrangements are used: forward trunk
fl exion on the hip with consequent hip stiffness or fl exion on the knees.
The choice of a strategy for balancing COG movements depends on personal
past experiences, on the individual history of previous accidents and pre-existent
muscle and joint impairments.
Therefore, although the ankle strategy is the most common pattern in cervical traumas, this does not mean that it must be found in all patients with whiplash injuries.
In interpreting Equitest results, the strategy analysis can infl uence the choice of
rehabilitative treatment; in cases of prevailing ankle strategy, we adopt exercises
S. Barozzi et al.
195
aimed at potentiating the extensor muscles and only afterwards exercises with the
purpose of recovering hip mobility.
In MCT the evaluation of latency offers interesting considerations: latencies
within normal ranges are observed either in forward or in backward translations
only in a limited number of patients with whiplash injuries. In our experience 86 %
of patients have abnormal latencies either in forward (10 %) or in backward translations (12 %) or in both (64 %). Response-strength scores and weight symmetry have
always been normal. In whiplash injuries abnormal latencies can be explained as
disorders in the afferent somatosensory pathways.
References
1. Johansson R, Magnusson M, Àkesson M (1988) Identifi cation of human posture dynamics.
IEEE Trans Biomed Eng 35:858–869
2. Johansson R, Magnusson M (1991) Human postural dynamics. Crit Rev Biomed Eng 18:
413–437
3. Black FO, Nashner LM (1982) Workshop III – information processing in the normal and
abnormal human postural control systems. Am J Otol 3(4):384–389
4. Black FO, Wall C 3rd, Nashner LM (1983) Effects of visual and support surface orientation refer-
ences upon postural control in vestibular defi cient subjects. Acta Otolaryngol 95(3–4):199–201
5. Nashner LM (1983) Analysis of movement control in man using the movable platform. Adv
Neurol 39:607–619
6. Black FO, Nashner LM (1984) Vestibulo-spinal control differs in patients with reduced versus
distorted vestibular function. Acta Otolaryngol Suppl 406:110–114
7. Nashner LM, Black FO, Wall C 3rd (1982) Adaptation to altered support and visual conditions
during stance: patients with vestibular defi cits. J Neurosci 2(5):536–544
8. Forssberg H, Nashner LM (1982) Ontogenetic development of postural control in man: adapta-
tion to altered support and visual conditions during stance. J Neurosci 2(5):545–552
9. Fitzpatrick R, Burke D, Gandevia SC (1996) Loop gain of refl exes controlling human standing
measured with the use of postural and vestibular disturbances. J Neurophysiol 76(6):3994–4008
10. Horak FB, Dickstein R, Peterka RJ (2002) Diabetic neuropathy and surface sway-referencing
disrupt somatosensory information for postural stability in stance. Somatosens Mot Res
19(4):316–326
11. Dietz V (1992) Human neuronal control of automatic functional movements: interaction
between central programs and afferent input. Physiol Rev 72(1):33–69
12. Magnusson M, Johansson K, Johansson BB (1994) Sensory stimulation promotes normaliza-
tion of postural control after stroke. Stroke 25:1176–1180
13. Gabell A, Simmons MB (1982) Balance coding. Phys Ther 68:286–288
14. Brandt T (1988) Sensory function and posture. In: Posture and gait, vol 812, International
congress series. Exerpta Medica, Amsterdam, pp 127–136
15. Norré ME (1990) Posture in otoneurology, vol I. Acta Otorhinolaryngol Belg 44:55–181
16. Chester JB Jr (1991) Whiplash, postural control, and the inner ear. Spine 16(7):716–720
17. Kogler A, Lindfors J, Odkvist LM, Ledin T (2000) Postural stability using different neck posi-
tions in normal subjects and patients with neck trauma. Acta Otolaryngol 120(2):151–155
18. Storaci R, Manelli A, Schiavone N, Mangia L, Prigione G, Sangiorgi S (2006) Whiplash injury
and oculomotor dysfunctions: clinical-posturographic correlations. Eur Spine J 15(12):1811–
1816, Epub Mar 22
19. Madeleine P, Prietzel H, Svarrer H, Arendt-Nielsen L (2004) Quantitative posturography
in altered sensory conditions: a way to assess balance instability in patients with chronic
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18 Dynamic Posturography
The Cervico-Cephalic Interaction
19
D.C. Alpini, V. Mattei, D. Riva, and F. Di Berardino
19.1 Introduction
While the first function of posture is an antigravity function, the second one is to
provide an interface with the external world for perception and action. For this
reason, body posture is built up by a set of assembled segments with own mass that
are linked together by flexible joints controlled by the neuromuscular system.
Posture based on the superimposed segments (the head, the trunk and legs) is under
the specific automatic central and peripheral control preserving the specific
orientation of each segment with respect to gravity and/or to the adjacent segment.
The central organization of posture involves interactions between external forces,
the mechanical properties of the body and the neuromuscular forces.
Head stabilization appears to be a necessary motor control [1] in order to provide
a stable orientation platform (regarding both gravity and environment landmarks)
necessary for an adequate progression of body movement. Input from different
systems are essential to control posture and head stabilization and it has been
postulated [2] that high motor and sensory mechanism are necessary both for
simplest conditions like standing (posture control) [3] and walking (head control).
D.C. Alpini (*) • V. Mattei
ENT-Otoneurology Service, IRCCS “Don Carlo C. Gnocchi” Foundation,
Milan, Italy
e-mail: dalpini@dongnocchi.it
D. Riva
International Society of Proprioception and Posture, via Valgioie 87,
10146 Torino, Italy
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
D.C. Alpini et al. (eds.), Whiplash Injuries,
DOI 10.1007/978-88-470-5486-8_19, © Springer-Verlag Italia 2014
197
198
D.C. Alpini et al.
Adequate posture and head controls are specific tasks of the vestibular system
[4], and they are particularly important in daily activities. Body is not a rigid block
but a flexible system formed by multiple segments tied together by the muscles surrounding the joints. When a movement is performed by a standing subject, like
walking, the geometry of the body is changed. Dynamic posture, in fact, can be
considered as superimposed modules from feet to the head, each linked to the next
by a set of muscles which have their own specific central and peripheral regulation
serving to maintain the module reference position. The reference position of each
the modules can be regulated independently from that of the others. Dysfunction of
cervical receptors in neck disorders has been shown to lead to disturbances in postural stability, causing a disruption of the intricate coordination between eye, neck
and trunk movements. These changes in cervico-cephalic coordination may underlie clinical symptoms reported by people with WAD that involve changes in function during walking [5].
The aim of the chapter is to describe specific instrumental tests able to investigate alteration of cervico-cephalic control provoked by whiplash.
19.2 CranioCorpoGraphy (CCG)
Head destabilization seems to be the specific target to investigate equilibrium dis-
turbances in whiplash patients. Since 1968, CranioCorpoGraphy (CCG) has been
used as a simple procedure to evaluate head-trunk stabilization in vestibular disorders [6]. It has proved to be one of the most efficient, quick, objective and quantitative tests for screening equilibrium function for nearly 20 years, and the West
German Labour Security Surveillance Board introduced it for occupational medi-
cal ability testing in 1983. CCG records light tracings from light bulbs on the
forehead, the occiput and both shoulders through a camera mounted from above
(Fig. 19.1).
The recording is displayed on film (Fig. 19.1b) from an instant camera fixed
above the head of the patient and directed towards a mirror on the ceiling. The results
are radar-like images, and the investigator evaluates a complete movement pattern
during stepping by visually inspecting the craniocorpogram. This enables the clinician to differentiate between vertigo of central and of peripheral origin [7, 8].
CranioCorpoGraphy (CCG) has been successively digitalized (dCCG) on the
basis of the optoelectronic technology [9]. Digital CranioCorpoGraphy (dCCG) is a
non-invasive assessment based on a 50 Hz CCD camera for acquiring the position
of four markers placed on the subject who walks on the spot (Fukuda Stepping test)
(Fig. 19.2).
A digital stepping analyzer (DSA.) recognizes these markers and identifies their
2D positions in the horizontal plane. These rough data are then transferred to a
workstation through a universal asynchronous receiver transmitter (UART) for processing and following elaborations. The UART allows a sampling rate of 25 Hz, and
so it fixes the maximum sampling rate of the whole system [9].
The output is a report that gives both analogue and quantitative information. The
subject performs the test blindfolded in a semi-darkened and sound-proofed room