Instrumented Wobble Board for Testing Functional Ankle Instability
Nicolaj Mentz Larsen
1
, Niclas Hvolby Andersen
1
, Mathilde Hansen
1
and Uffe Laessoe
1,2
1
Department of Physiotherapy, University College of Northern Denmark, Selma Lagerloffsvej, Aalborg, Denmark
2
Research and Development Department, UCN, Aalborg, Denmark
Keywords: Ankle Sprain, Chronic Ankle Instability, Ankle Disc, Assessment.
Abstract: Lateral ankle distortion is one of the most frequent sports injuries. In approximately 40% of the incidents, the
individual will develop chronic ankle instability. Ankle instability is not detected consistently using traditional
balance measures and alternative approaches are warranted. It was hypothesized that an instrumented wobble
board may serve as a tool to detect people with functional ankle instability.
Twenty-two young people with perceived ankle instability and a gender and age-matched control group were
included in the study. The participants were standing on one leg for 30 seconds on an instrumented wobble
board - with and without visual performance feedback. The primary outcome measures were the standard
deviations of the tilt angle in the medio-lateral and the anterior-posterior directions.
The tilt variation in medio-lateral direction was significantly larger in the instability group: with feedback
1.65 (0.72) vs. 1.14 (0.31) and without feedback: 1.95 (1.01) vs. 1.20 (0.35). Similar, but not statistically
significant, differences were seen in anterior-posterior direction.
Participants with chronic ankle instability display increased tilt variation when challenged in one-leg stance
on a wobble board. The tilt inclination measured by an instrumented wobble board may serve as a
supplementary objective measure for the clinical identification of people with functional ankle instability.
1 INTRODUCTION
Lateral ankle distortion is one of the most frequent
sports injuries and may be associated with recurrent
distortions, pain and other symptoms (Hertel, 2002).
In approximately 40% of the incidents, the individual
will develop chronic ankle instability, which is
defined as recurrent distortions and episodes of
instability over a period exceeding six months
(Hubbard, 2007).
Chronic ankle instability may appear as a
mechanical or a functional instability, or as a
combination of these types (Levin et al., 2012).
Mechanical ankle instability refers to laxity of the
joint after an injury to the stabilizing structures
(Munn et al., 2009). Functional ankle instability
(FAI) is also a widely used term, but the definition of
this condition is not as well established (Delahunt et
al., 2010). In the present study, FAI is defined as one
or more episodes of lateral ankle sprain followed by
experiences of instability.
It is not clear what causes the functional
instability, but it is proposed that the condition may
be a result of a dysfunctional sensorimotor system
(Hertel, 2002). A recent review provides guidelines
for the examination and treatment of ankle instability,
but this review also states that the role of the neuro-
muscular elements in subjective instability is
controversial and needs further study (Martin et al.,
2013).
Functional impairment in people with chronic
ankle instability has not been detected consistently by
the use of traditional instrumented outcome measures
for evaluating balance (McKeon and Hertel, 2008).
The use of other measures than postural sway, more
closely linked to functional ankle stability, has
therefore been suggested (Hupperetset al., 2009). In
the present study, we used an instrumented wobble
board (also called ankle disc). Standing on one leg on
a wobble board represents a task that requires
dynamic stability of the ankle.
The aim of this study was to investigate whether a
test on an instrumented wobble board could identify
impairment in ankle stability. It was hypothesized
that the performance, while standing on one leg on a
wobble board, would be less stable for people with
self-reported functional ankle instability.
Larsen, N., Andersen, N., Hansen, M. and Laessoe, U.
Instrumented Wobble Board for Testing Functional Ankle Instability.
DOI: 10.5220/0006919901190123
In Proceedings of the 6th International Congress on Sport Sciences Research and Technology Support (icSPORTS 2018), pages 119-123
ISBN: 978-989-758-325-4
Copyright © 2018 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved
119
2 METHODS
The study was designed as a case-control study to
evaluate the construct validity of the test. A
convenience sample of 22 people with functional
ankle instability was recruited for the case group
through public announcement.
Inclusion criteria were: aged 18-30 years; several
episodes of lateral ankle distortions or experiences of
instability within the previous six months and a
minimum score of 11 on a questionnaire on functional
ankle instability (IdFAI) (Gribble et al., 2014).
Exclusion criteria were: previous fractures of lower
extremities; pain, edema or movement restrictions
within the last six weeks. The control group was an
age and gender matched group of 22 healthy people
with IdFAI score below 11. All participants reported
physical activity for at least four hours a week.
The study was conducted in accordance with the
guidelines of the regional research ethics committee
of Northern Denmark and informed consent was
obtained from all participants in accordance with the
Declaration of Helsinki.
2.1 Outcome Measures
Questionnaire
The case group was characterized by the
“Identification of Functional Ankle Instability
questionnaire” (IdFAI). This questionnaire is
developed to detect whether individuals meet the
minimum criteria necessary for inclusion in a FAI
population (Simon et al., 2012). It defines functional
ankle instability as the tendency of the foot to ‘give
way’. This is described as a temporary uncontrollable
sensation of instability or rolling over of one’s ankle.
The reliability of the questionnaire has been
established in other studies (Gurav et al., 2014). The
questionnaire consists of ten questions, which are
ranked on the experienced severity of the impairment.
The questions address one ankle only.
Instrumented Wobble Board
The ankle stability was evaluated while the
participant was standing for 30 seconds on one leg on
an instrumented wobble board, SensBalance Mini
board (Sensamove, Netherland). This tool is a
wooden wobble board with two accelerometers
placed horizontally in anterior-posterior plane (AP)
and medio-lateral plane (ML) respectively. Any tilt in
the direction of the sensor is detected as an
acceleration signal with reference to the earth’
gravity. In this way the accelerometers reflect the tilt
movements of the board.
It is possible to get a continuous feedback on the
balance performance from a monitor where a dot on
a target represents the tilt of the wobble board. With
no tilt, the dot will be in the center of the target. In
this way a visual performance feedback may be
provided for the participant.
Several levels of difficulties may be chosen for the
board. In this study, the maximum tilt of the board
was 15 degrees and the accelerometer sample
frequency was 22 Hz.
The custom software presents the averaged tilt of
the wobble board by a 0-100% score in a user
interface. These averaged figures may be misguiding,
however, as an otherwise stable position in a five
degrees tilt position will give a low score.
Furthermore, they are not representative for the
ongoing corrections representing the ankle stability.
The data representing the wobble board angular tilt in
AP and ML direction for all samples was therefore
exported from the SensBalance custom software to
MS Excel for further analysis.
The standard deviation of the tilt positions during
the 30 seconds of testing was calculated for the two
directions and this variance measure represented the
outcome measure for the stability performance.
2.2 Procedure
The participants were allowed time to get accustomed
to standing on the wobble board. They were asked to
stand on the board on one leg with bare feet. The case
group stood on the leg with the impaired ankle and
the control group stood on their dominant leg.
They were tested with open eyes under two
conditions. One condition provided continuous target
feedback from a monitor placed in 1.5 meters height
1.5 meter away. In the other condition, they were
asked to look at the same spot, but with no target
feedback. The sequence of the tests was randomized.
If they lost their balance, they were allowed another
try up until three trials.
2.3 Data Analysis
The baseline data for the two groups was compared
by independent T-test and Chi-test to evaluate the
match of the control group to the case group on age,
gender, BMI and IdFAI.
The performance scores (i.e. the standard
deviation of the wobble board angular tilt) were
presented by mean and sd. for the anterior-posterior
and medio-lateral directions. The group performance
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was compared by Mann-Whitney U-test as some data
displayed lack of normally distribution.
Correlations between the IdFAI scores and the
stability scores were evaluated for the common score
of the two groups by Spearman’s correlations
coefficients. The statistical analyses were done in
SPSS and the level of statistical significance was set
at 0.05.
3 RESULTS
The two groups were comparable with respect to age,
gender, height and weight. The IdFAI score was
higher in the case-group (Table 1).
Table 1: Group characteristics.
Control
Case group
Gender (female/male)
17 / 5
18 / 4
Age (years)
23.6 (1.8)
23.6 (2.1)
Height (m)
1.72 (0.11)
1.72 (0.08)
Body mass (kg)
71.2 (13.5)
70.9 (10.2)
IdFAI score
2.6 (2.1)
17.6 (4.3) *
Mean values and SD. p<0.01
3.1 Performance
The case group showed increased instability when
standing on the wobbleboard compared to the control
group. This was, however, only statistically
significant in the medio-lateral direction. The
difference was seen in the condition with visual target
feedback as well as in the condition without target
feedback. There was no difference between the two
feedback conditions in either group (Table 2).
3.2 Correlation with Id FAI
There were only weak correlations between the FAI
score and the instability measures, and these
correlations were significant only for the medio-
lateral instability in the two tasks (Table 3).
The instability measures in the two directions
antero-posterior and medio-lateral correlated
significantly. In addition, these instability measures
correlated for the two conditions with and without
target feedback.
4 DISCUSSION
4.1 Identification of Stability
Impairment
Compared to a healthy control group, the participants
with chronic ankle instability displayed increased
instability when challenged in one-leg stance on a
wobble board.
It is uncertain what causes functional ankle
instability (FAI), but it may occur due to a
dysfunctional sensorimotor system. Damage to
capsular and ligamentous structures may result in
impaired proprioception and consequently reduce the
ability to maintain postural control and balance
(Hertel, 2002). Larger deviations in the tilt of the
wobble board is seen with reduced sensory input
(closed eyes) and this suggests that a large standard
Table 2: Instability while standing on wobble board.
Control group
Case group
Performance with target feed-back
Anterior-posterior tilt variation
0.97 (0.26)
1.20 (0.55)
Medio-lateral tilt variation
1.14 (0.31)
1.65 (0.72)
Performance with no target feed-back
Anterior-posterior tilt variation
0.96 (0.24)
1.24 (0.61)
Medio-lateral tilt variation
1.20 (0.35)
1.95 (1.01)
Group mean values and SD representing the variation in tilt (degrees) of the wobble board (i.e. standard
deviation of the angular tilt during 30 seconds of testing).
* p<0.05
Instrumented Wobble Board for Testing Functional Ankle Instability
121
Table 3: Correlations between the IdFAI questionnaire and the instability measures.
AP_target
ML_target
AP_no-target
ML_no-target
IdFAI
0.14
0.32*
0.28
0.34*
ML_no-target
0.43**
0.51**
0.62**
AP_no-target
0.64**
0.53**
ML_target
0.77**
Spearman’s correlations coefficients (r)
* p<0.05; **p<0.01
deviation of the tilt angle reflects reduced postural
capacity (Williams and Bentman, 2014).
The instability and higher adjustment activity
observed in the case-group in the present study was
most likely a consequence of impaired ankle control,
but the study design allows no unequivocal
conclusion in this respect.
Although a statistically significant difference was
observed in the performance of the two groups, no
strong correlation between idFAI and the stability
performance was seen. This may mainly be ascribed
to a high variation in the performance of the case-
group. Some of the participants with high idFAI score
performed just as well or better on the wobble-board
as participants from the control group. A possible
explanation could be, that more individuals in the
case-group had experiences with the wobble board, as
this tool is often used for rehabilitation after an ankle
sprain. The control of the wobble board tilt is
naturally related to ankle stability, but also other
aspects of balance control may influence this
performance. Still, the test may provide objective data
to supplement the self-reported condition of the
individual.
As lateral ankle distortion may be associated with
recurrent distortions (Hertel, 2002) athletes with
functional ankle instability should be identified in
order to offer them training and restore function
(Oliveira et al., 2013). The use of traditional
instrumented outcome measures for evaluating
balance may not always be sufficiently challenging in
order to detect ankle instability (McKeon and Hertel,
2008). Measures, more closely linked to functional
ankle stability, may therefore be warranted to identify
ankle instability (Hupperets et al., 2009). The
unstable support surface of a wobble-board will
increase the level of difficulty of maintaining postural
control in a standing position and the ankle stability
control will be particularly challenged in this task
(Ogaya et al., 2011; Shumway-Cook and Woollacott,
2007). Compared to a test on a stable balance
platform or a force plate the test on a wobble board
represents a more difficult stability challenge, and
this may avoid a possible ceiling effect when testing
an individual with minor impairment.
4.2 Instrumentation of Wobble Board
Different types of instrumented wobble boards have
become commercially available on the market, and
these tools may prove helpful in the assessment of
balance impairment and ankle instability (Williams
and Bentman, 2014). According to the findings in the
present study, the user-interface of such instruments
should provide a presentation of variability measures
for the evaluation of the performance. Furthermore, it
must be emphasized that there is a need for a
standardization of the procedures for wobble board
testing. To compare different recordings, the length
of the testing sequence, the visual fixation, the
placement of non-supporting leg etc. must be
standardized.
The development of new technologies provides
new possibilities for clinical testing. With respect to
instrumented wobble boards, one cheap option may
be suggested here. With a smartphone is attached to
the wobble board the accelerometer sensors in the
smartphone will measure the movements of the
wobble-board. This data may be sufficient for further
analysis by an app.
The participants were tested during two
conditions: with and without target feedback. It is
well known that the balance is depending on visual,
proprioceptive and vestibular input and that the
balance is more challenged with closed eyes (Isakov
and Mizrahi, 1997). It was expected that a similar
difference could be seen between conditions with and
without visual target feedback. This was not evident
in this study, however. In both conditions, the
participants had open eyes and the difference in target
feedback had apparently no discriminating influence
on the performance in either of the two groups.
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5 CONCLUSION
Participants with chronic ankle instability display
increased tilt variation when challenged in one-leg
stance on a wobble board. The tilt variation measured
by an instrumented wobble board may serve as a
supplementary objective measure for the clinical
identification of people with functional ankle
instability and as a measure for performance
improvement.
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