The effects of sensory stimulation on postural stability after whiplash injury

Individuals with chronic neck and shoulder problems caused by whiplash injury
not only suffer from pain in these areas, but they also often tend to have
dizziness complaints, concentration problems, hypersensitivity to sensory
information/stimulation, and a disturbed balance system. These complaints are
collectively known in the literature as whiplash associated disorders (WAD). A
crucial factor in disturbed balance appears to be that the different sensory
modalities that are used for the regulation of balance are not properly tuned.
A key aspect of rehabilitation is aimed at reducing the whiplash associated
sensory complaints. This is known in therapeutic circles as sensory integration
therapy (SI). However, at the moment little scientific knowledge exists on how
the senses work together in the regulation of balance. The aim of this research
is to investigate -using posturography- what the effects are of sensory
manipulations on the regulation of balance in WAD patients. A group of 15 WAD
patients and 15 unaffected controls will perform a number of simple balance
tests. At the same time, movements of the body center of pressure will be
recorded using a force plate.

The aim of this research is to examine the effects of changes in proprioceptive
and visual information on balance control in WAD sufferers. Although clinical
experience suggests more effective balance control due to elevated
proprioceptive information, this has never been quantified using objective
posturographic measures. Balance will be measured by recordings of body sway,
or more technically, the centre of pressure (COP) time-series registered with a
force plate.
The following questions will be addressed:
* Is balance control in the WAD group less efficient than in a control group?
* In the WAD group, will balance control benefit from added proprioceptive
input?
* In the WAD group, will balance control suffer from added visual input?
* What are the combined effects of the WAD syndrome and the availability of
sensory signals on postural control?

Before the experiment begin participants sign the informed consent. Prior to
the recording of the balance, participants (both patients and controls) are
asked to fill out the Dutch equivalent of the following three questionnaires.
1) The Dutch version of the dizziness Handicap Inventory (DHI), which measures
the subjective impact of dizziness on the everyday life of the participants.
2) The Tampa Scale for Kinesiophobia to assess pain related fear of movement.
For unaffected controls the modified version of the TSK will be used.
3) The Beck Depression Inventory.
These questionnaires are standard use in clinical routine and scientific
investigations of chronic pain patients, including WAD.

Upon arrival in the measurement lab and after the forms have been collected by
the experimenter, patients are asked to indicate their level of actual
experienced pain on a Visual Analogue Scale (VAS), on a 100-points scale (0 =
no pain; 100 severe pain).
For the collection of the balance data, participants (patients and controls)
will stand on a forceplate, adopting a natural and comfortable stance position,
with the arms hanging relaxed alongside the body. Participants will be standing
bare footed or wearing socks but no shoes or sandals, in order to maximize the
quality of the posturographic measurements. In some conditions a belt weighing
500 g will be worn around the waist. This belt is part of the occupational
therapist's toolbox when conducting sensory integration therapy.
Two different tasks will be performed. First, static balance capability
(conditions A1 to A4) will be measured. During the static balance conditions
participants will be asked to maintain quiet stance and to look straight ahead.
In the experimental conditions the availability of visual and proprioceptive
information is manipulated, as follows:
- A1: quiet standing (baseline)
- A2: quiet standing + 500 g waist belt
These 2 conditions are repeated, but participants will see a coloured spot (dot
of approximately 5 mm) on a monitor in front of them that gives participants
instantaneous visual information of the position (and changes therein) of their
centre of pressure (COP). Thus, vision is added as an extra source of feedback
for balance control. The instruction will be to keep this dot within the
confines of a circle of a larger radius. This will result in 2 additional
conditions:
- A3: quiet standing + visual feedback
- A4: quiet standing + 500 g waist belt + visual feedback
Second, dynamic balance (conditions B1 to B4) will be measured. During the
dynamic balance conditions participants will be asked to periodically shift
their weight from their left leg to their right leg and back again, which
thereby results in medio-lateral displacements of their COP. In all conditions
participants will receive visual feedback of their COP, similar to conditions
A3/A4. In conditions B1 and B2 the task is to perform a set of rhythmic weight
shifts so that the feedback dot on the screen oscillates rhythmically from left
to right, thereby keeping the dot within the area enclosed by two vertical bars.
- B1: weight shifting (baseline)
- B2: weight shifting + 500 g waist belt
Also, participants have to perform a task, in which they are asked to
move the feedback dot between moving objects (slowly moving squares) and try
not to *collide' with any of the blocks:
- B3: virtual collision avoidance
- B4: virtual collision avoidance + 500 g waist belt
The static balance (A1 to A4) will have a duration of 1 minute each. The
dynamic balance conditions (B1 to B4) will have duration of 2 minutes each.
Each condition will be repeated 2 times. Between each condition, participants
can take a rest upon request, during which they are allowed to leave the force
plate and sit down if they want. All participants will wear headphones to
filter out possible background noise, as this might distract attention from the
task. No verbal cues will be given to the participants during the tests. The
static balance and dynamic balance conditions will be presented in a block, but
within a block the conditions 1 to 4 will be presented in a random order.

See Study design

During the experiment participants will have the opportunity to grab a
handrail, located on the left and right side of the force plate, if they
experience dizziness or discomfort. Subjects will also be closely monitored by
an experimenter. Participants are free to take a small rest (or even abort the
experiment) when they experience too much discomfort, fatigue, or dizziness. We
expect hardly any instances of discomfort, fatigue, or dizziness due to the
very low level of physical activity of the conditions and due to the low
complexity of the visual signal.