Observations of four children with severe cerebral palsy using a novel dynamic platform. A case report

Abstract

The aim was to evaluate effects on bone mineral content (BMC) in children with severe cerebral palsy (CP) standing on a self-controlled dynamic platform (vibrations, jumps and rotation), assess reactions expressed and record negative effects. An experimental design was used. Four children with severe CP participated. Two children used the platform for 8–9 months while two children were controls (period I). After 1 year, the former users were controls (period II). Dual-energy X-ray absorptiometry was performed. Children in period I (Child 1/Child 2) were exposed to whole body vibration for 330/394 min on 28/25 occasions and showed a percentage change in BMC values at the lumbar spine of +35/+23% (versus controls, Child 3/Child 4, −9/+7%), left legs −9/ −12% (vs. −2/ −12%) and right legs +61/+34% (vs. −18/+10%). Children in period II (Child 3/Child 4) were exposed for 524/635 min on 57/64 occasions. The corresponding percentage change in BMC values at the lumbar spine was +10/+10% (+21/+5%), left legs +26/+22% (0/+5%) and right legs +26/+17% (+15/ −1%). The children's reactions were perceived positive. No negative effects were recorded. Standing on a self-controlled dynamic platform may be an enjoyable method to increase BMC in children with severe CP.

Full text

Correspondence: Ylva Dal é n, Department of Neurobiology, Care Sciences, and Society, Division of Physiotherapy, Karolinska Institutet, Stockholm, Sweden.
E-mail: ylva.dalen@jumpandjoy.se
(Rece ived 29 December 2011 ; accept ed 11 May 2012 )
(GH) secretion. Insuffi cient nutrition causes a reduc-
tion in circulating IGF-I in spite of adequate GH-
levels. Thus children with poor nutrition do not grow,
even if they have a normal production of GH (4).
The primary requirement of bones is to provide
rigid leverage for muscle pull while remaining as light
as possible (5). This means that the shape and archi-
tecture of the bone needs to adapt to use. This adap-
tation is driven by dynamic, rather than static loading
(6). The most common fracture site in these children
is the distal femur, and the risk of fracture increases
with previous fractures (7). The immature skeleton
is more responsive to mechanical loading (3), and
normally, bone density reaches peak values at differ-
ent sites of the body around the age of 19 – 30 years
(8). It is a challenge to create an environment
where mechanical loading is made possible, also for
children with severe disabilities.
ORIGINAL ARTICLE
Observations of four children with severe cerebral palsy using a novel
dynamic platform. A case report
Y LVA DAL É N
1 , MARIA S Ä Ä F
2 , SVEN NYR É N
2 , EVA MATTSSON
1 ,
YVONNE HAGLUND- Å KERLIND
3 & BRITA KLEFBECK
1
1 Department of Neurobiology, Care Sciences, and Society, Division of Physiotherapy, Karolinska Institutet, Stockholm, Sweden,
2 Department of Molecular Medicine and Surgery, Karolinska University Hospital, Karolinska Institutet, Stockholm, Sweden, and
3 Department of Women ’ s and Children ’ s Health, Karolinska University Hospital, Karolinska Institutet, Stockholm, Sweden
Abstract
The aim was to evaluate effects on bone mineral content (BMC) in children with severe cerebral palsy (CP) standing on
a self-controlled dynamic platform (vibrations, jumps and rotation), assess reactions expressed and record negative effects.
An experimental design was used. Four children with severe CP participated. Two children used the platform for 8–9
months while two children were controls (period I). After 1 year, the former users were controls (period II). Dual-energy
X-ray absorptiometry was performed. Children in period I (Child 1/Child 2) were exposed to whole body vibration for
330/394 min on 28/25 occasions and showed a percentage change in BMC values at the lumbar spine of +35/+23% (ver-
sus controls, Child 3/Child 4, −9/+7%), left legs −9/−12% (vs. −2/−12%) and right legs +61/+34% (vs. −18/+10%).
Children in period II (Child 3/Child 4) were exposed for 524/635 min on 57/64 occasions. The corresponding percentage
change in BMC values at the lumbar spine was +10/+10% (+21/+5%), left legs +26/+22% (0/+5%) and right legs
+26/+17% (+15/−1%). The children’s reactions were perceived positive. No negative effects were recorded. Standing on a
self-controlled dynamic platform may be an enjoyable method to increase BMC in children with severe CP.
Key words: biomechanics , mechanical loading , musculoskeletal , orthopaedics , paediatrics
Advances in Physiotherapy, 2012; 14: 132–139
ISSN 1403-8196 print/ISSN 1651-1948 online © 2012 Infor ma Healthcare
DOI : 10. 3109 /140 38196.2012.6 93948
Introduction
Dynamic mechanical loading of the skeleton is diffi -
cult to obtain in children with severe cerebral palsy
(CP). They are unable to attain an upright position
and are consequently restrained from playful, dynamic
loading of the skeleton, which is stimulating for healthy
children. Dynamic weight bearing is an important fac-
tor for increasing bone strength and bone structure,
and the lack of dynamic weight bearing contributes to
osteoporosis, which leads to an increased risk of frac-
tures and hip dislocation in these children (1,2).
Malnutrition and anti-epileptic medicine have
also been reported to contribute to osteoporosis in
these children (3). An analysis of insulin-like growth
factor-I (IGF-I) in the blood can indicate whether a
child has a suffi cient nutrition. Circulating IGF-I in
the blood is produced mainly in the liver and normal
levels depend on both nutrition and growth hormone
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Whole body vibration in children with severe CP 133
with CP. A 3-month period of home-based exposure
to vibration on a side-alternating platform increased
total body BMD and BMC ( p ⫽ 0.001). Ruck et al.
(25) performed a randomized controlled study expos-
ing 10 children with CP to vibration. That study
showed an increase in mobility but a decrease in dis-
tal femur diaphysis vBMD. Several animal studies
(26 – 28) show the possibilities of improvement of the
skeletal architecture by using WBV. However, the
effect of WBV on BMC has not been studied in chil-
dren using a standing shell.
In order to optimize the effects of standing, a
vibrating platform with supplementary functions has
been constructed (Figure 1).
The aim of the present study was to assess the
children ’ s expressed feelings, to record any negative
effects and to evaluate the effects on BMC in chil-
dren with severe CP standing on the dynamic plat-
form with WBV.
Material and methods
The study design was experimental, including two
periods of 8–9 months, with baseline and end-of-
period measurements in both periods. The parents
of fi ve Swedish children with severe CP, four boys
and one girl, responded to an advertisement on the
website of the National Association for Disabled
Children and Youths (RBU). The parents of one
Dual-energy X-ray absorptiometry (DXA) is the
most commonly employed technique for measuring
bone mass. The radiation is very low (1 – 4 μ Sv), but
both precision (0.8 – 2.5% in children) and accuracy
are high (9). From the DXA measurements, body
composition, areal bone mineral density (BMD g/
cm
2 ) and bone mineral content (BMC, g) can be
derived.
The skeleton and hip anatomy at birth is mostly
normal in children with CP, but lack of weight bear-
ing, in combination with spastic muscles, contributes
to osteoporosis and also to dislocation of the hip (10).
This may lead to pain, contractures, problems sitting
or standing, fractures, pelvic obliquity, scoliosis and
‘ windswept hip ’ (11). Gunter et al. performed a study
with a 7-month weight-bearing regimen (jumping on
the fl oor) in 33 non-disabled pre-pubertal schoolchil-
dren that showed a 3.6% increase in BMC at the hip
compared with controls and a sustained gain of 1.4%
was maintained after 7 years (12).
In children with severe CP, standing devices are
commonly used to obtain an upright position and are
intended to contribute to stretching the muscles (13)
and increasing bone mass, but the amount of weight
bearing in the devices varies greatly between indi-
viduals (14). Furthermore, standing in passive devices
does not seem to affect BMD in the lower limbs,
where most fractures occur (15). A standing device
called the standing shell was invented in Sweden in
the 1980s. The standing shell is an individually
moulded plaster cast formed around the legs and
back of the child and fastened in front with straps,
and is commonly used in clinical practice in Sweden.
The Swedish National Health Care Quality Program
for prevention of hip dislocation and severe contrac-
tures in Cerebral Palsy (CPUP) found that 67% of
a cohort of 276 children aged 3 – 18 years with severe
CP used a standing shell in 2009 (16). The recom-
mended standing time in Sweden is 1 – 2 h daily (17)
but the effects of standing on BMC have not been
completely evaluated (18,19).
Vibration administered locally to muscle groups
has been used by physiotherapists for several decades
to decrease spasticity in children with CP (20,21).
Whole body vibration (WBV) in a standing position
has been reported to decrease spasticity in persons
with CP (22). Ward et al. (23) performed a controlled
study including 20 disabled, ambulant children with
CP, 4 – 19 years of age, who were randomized to stand
on an active, vertically vibrating platform or on a
placebo device for 10 months. That study showed a
mean change in proximal tibia volumetric trabecular
BMD (vBMD; mg/ml) of 6% increase in the inter-
vention group compared with 11.9% decrease in the
control group ( p ⫽ 0.003). Stark et al. (24) performed
a retrospective data analysis including 78 children Figure 1. The novel vibrating platform with a standing shell.
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134 Y. Dalén et al.
child withdrew after the fi rst session of measure-
ments. That child never used the platform.
Participants
Four children aged 4 – 6 years (median age 4 years)
at the start of the study participated. The children
were classifi ed according to the Gross Motor Func-
tion Classifi cation System (GMFCS) developed by
Palisano et al. (29), on a scale of I – V, where V indi-
cates the most severe form of CP. The participating
children were all classifi ed as GMFCS score V. The
degree of spasticity was assessed on hip fl exors and
adductors by the children ’ s ordinary physiotherapist
using the modifi ed Ashworth scale, according to
Peacock & Staudt (30). Possible scores range from
0 ⫽ hypotonic, 1 ⫽ nor mal, 2 ⫽ mild, 3 ⫽ moderate
and 4 ⫽ severe, to 5 ⫽ extreme spasticity. Results of
the assessments obtained from the children ’ s medical
fi les showed that the participating children had a
spasticity level of 2 – 3 in their hip fl exors and/or
adductors and they were all given Botulinum toxin
in muscles infl uencing the hip region as recom-
mended in the ordinary orthopaedic routines for
each child. One child was gastrostomized (Child 2)
due to problems with oral feeding.
The children ’ s social function was assessed by the
Pediatric Evaluation of Disability Inventory (PEDI),
developed by the PEDI research group (Boston Uni-
versity, 635 Commonwealth Avenue, Boston, MA,
USA). Scaled scores provide an indication of the per-
formance of the child along the continuum (0 – 100)
of relatively easy to relatively diffi cult items. For a
description of the children, see Table I.
Methods
Anthropometric measurements were undertaken at
Astrid Lindgren ’ s Children ’ s Hospital, Karolinska
University Hospital, in Stockholm, Sweden. Recum-
bent body height was measured with a rigid measuring
tape. Weight was measured by placing the lightly
clothed child in a digital weight chair. Values for height,
Table I. Anthropometric data of each child at the beginning of the study.
Height
(SDS)
Weight
(SDS)
BMI
(SDS)
IGF-I
(SDS)
GH,
μ /ml ICD 10
PEDI
Scaled
score
Child 1 ⫹ 0.01 ⫺ 1.72 ⫺ 2.54 ⫺ 0.112 5.2 G 809 dyskinetic 47.3
Child 2 ⫹ 1.10 ⫹ 0.78 ⫹ 0.25 ⫺ 0.717 0.1 G 808 spastic 32.9
Child 3 ⫺ 1.20 ⫺ 1.23 ⫺ 0.08 ⫺ 2.185 0.8 G 808 spastic 30.0
Child 4 ⫺ 3.38 ⫺ 3.33 ⫺ 0.22 ⫹ 0.121 1.7 G 803 dyskinetic 41.8
Height, weight, body mass index (BMI), insulin-like growth factor-I (IGF-I) shown as age-matched standard deviation score (SDS).
Growth hormone ( μ /ml), International Classifi cation of Diseases (ICD 10), and Pediatric Evaluation of Disability Inventory (PEDI, scaled
score 0 – 100).
weight and BMI were compared with age-matched
Swedish healthy children expressed as SDS (standard
deviation score) using an electronic calculator (31).
DXA (Hologic 4500; Hologic Inc., Bedford, MA,
USA), was used to assess the BMC at the lumbar
spine and in the whole body. From the latter mea-
surement, regions of interest (ROI) of the entire right
and left legs including hip regions were used to
retrieve BMC values.
The DXA equipment was tested by repeated mea-
surements with a coeffi cient of variation of 0.8% for
the total body and 2.5% for the lumbar spine. The
DXA measurements were performed under sedation
using Stesolid (Inpac AS, Lierskogen, Norway).
A platform was constructed. It was controlled by
the children through a manoeuvre panel with colour-
ful push buttons that allows children to rotate the
platform 90 ° right or left, to raise and lower the plat-
form by 0.2 m, and to create vibration and sounds.
The frequency of the vibration can be set at a range
from 20 to 64 Hz; the peak-to-peak displacement is
0.3 mm in an unloaded setting, causing tender vibra-
tions, allowing children to stand with straight legs in
their standing shells. Direct, vertical vibrations were
used. Since the vibrating platform was a prototype,
caution was necessary and the study was divided into
periods I and II. As the results of period I did not
raise any concerns, period II commenced with a
more structured design.
Period I . Child 1 and Child 2 used the platform for
8 or 9 months while Child 3 and Child 4 were con-
trols. The platform was used at the children ’ s school
at the convenience of the personnel and the child.
No instruction was given as to how often each child
was to be placed in the platform. The children could
choose to vibrate at a continuous variable frequency
in the range of 20 – 64 Hz and the duration of vibra-
tion was digitally recorded. They could choose to use
the other functions (rotation and raising and lower-
ing) as they wished.
Period II . Child 3 and Child 4 used the platform for
8 or 9 months, while Child 1 and Child 2 were controls.
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Whole body vibration in children with severe CP 135
Again the platform was used at the children ’ s school,
but during this period, the personnel were instructed
to put the children in the platform two to three times
a week. The exposed children in period II were not
able to control the vibration in contrast to the ex-
posed children in period I, but they could chose to
use the other functions as they wished. The vibration
was set to 10 min using a stopwatch and the frequen-
cy was set to 50 Hz.
In periods when the children were not exposed
to vibration, they used their standing shells on a daily
bases, which is normal routine.
Parents and personnel interpreted the feelings
shown through the facial expressions of the child
when using the platform and were asked to report
any negative effects from the use of the platform .
Prior to the study, written informed consent was
obtained from the parents, and information was pro-
vided to the children ’ s paediatricians. The study was
approved by the local ethics and radiation protection
committees at Karolinska University Hospital in
Stockholm, Sweden. The Swedish Medical Products
Agency was informed.
Statistics
The results, presented as median (and range), were
not statistically analysed due to the few partici-
pants.
Results
Between period I and period II, the DXA measure-
ment equipment was upgraded and the digital detec-
tors and software were replaced. This increased the
sensitivity to areas of low bone mass and the detected
values changed considerably as larger areas of bone
were included. This had an obvious effect on BMC
detection in these children with extremely low bone
density. Thus, the absolute BMC values could not be
compared between the periods as the measurements
before and after the upgrade were too dissimilar.
Height (cm), weight (kg), lean body mass (lean,
g), total body mass (total, g) and percentage (fat %)
before and after periods of exposure of WBV in each
child are shown in Table II.
Height and weight standard deviation scores
showed no major changes before and after periods of
exposure of WBV (data not shown).
Table III shows BMC values before and after
periods of exposure and control in each child. Table
IV shows BMD values before and after periods of
exposure and control in each child.
Children in period I (Child 1/Child 2) were
exposed to WBV for 330/394 min on 28/25 occasions
(Table V) and showed a percentage change in BMC
values at the lumbar spine of ⫹ 35/ ⫹ 23% (versus con-
trols, Child 3/Child 4, ⫺ 9/ ⫹ 7%), left legs ⫺ 9/ ⫺ 12%
(vs. ⫺ 2/ ⫺ 12%) and right legs ⫹ 61/ ⫹ 34% (vs.
⫺ 18/ ⫹ 10%) (Figure 2). Children in period II (Child
3/Child 4) were exposed for 524/635 min on 57/64
occasions (Table V). Corresponding percentage change
in BMC values at the lumbar spine was ⫹ 10/ ⫹ 10%
( ⫹ 21/ ⫹ 5%), left legs ⫹ 26/ ⫹ 22% (0/ ⫹ 5%) and
right legs ⫹ 26/ ⫹ 17% ( ⫹ 15/ ⫺ 1%) (Figure 3).
The vibrating platform seemed to be well accepted
by the children. Citations of the parent ’ s and person-
nel ’ s interpretation of the children ’ s facial expres-
sions when using the platform are presented in Table
VI. No negative effects were recorded.
Discussion
The present pilot study showed a tendency of increas-
ing BMC values at the lumbar spine and at the right
legs during the ad lib period I (Figure 2) and increasing
BMC at the lumbar spine and both legs during period
II (Figure 3) with more intensive exposure in children
with severe CP. The children, who expressed positive
feelings, seemed to enjoy the exercise (Table VI).
The percentage change in BMC values between
baseline and the end of period I showed four negative
values for the non-exposed children, while the per-
centage change in the exposed children was negative
only for the left leg. In period II, all children showed
positive percentage change in BMC values, i.e. even
the two non-exposed children, who had previously
been exposed to the WBV in period I. In period I,
Table II. Values in height (cm), weight (kg), lean body mass (lean, g), total body mass (total, g) and percentage fat (%) before and after
periods of exposure of vibration in each child.
Height (cm) Weight (kg) Lean (g) Total (g) Fat %
Exp (min)Before After Before After Before After Before After Before After
Child 1 100 104 13.3 13.7 9631 1156 1243 1476 19.8 18.7 330
Child 2 106 113 17.0 19.7 12149 1195 1795 1843 30.4 33.0 394
Child 3 97 103 14.4 14.7 11171 1069 1445 1407 20.4 21.6 524
Child 4 101 105 17.3 20.5 14368 1415 1841 1971 19.4 25.5 635
Amount of minutes of exposure to vibration for each child [Exp (min)].
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136 Y. Dalén et al.
Table III. Values of bone mineral content (g) at the lumbar spine, the entire right leg and the entire left leg before and after periods of
exposure of vibration and periods of control in each child.
Lumbar spine
exposure
Lumbar spine
control
Right leg
exposure
Right leg
control
Left leg
exposure
Left leg
control
Before After Before After Before After Before After Before After Before After
Child 1 8.7 11.8 13.6 15.3 14.7 23.6 65.4 75.3 24.8 22.5 69.3 73.4
Child 2 8.2 10.12 12.2 12.2 31.7 42.5 84.5 83.9 37.1 32.8 87.9 91.8
Child 3 10.6 11.7 9.3 9.3 51.8 65.5 20.8 14.6 50.4 63.4 16.1 14.8
Child 4 12.6 13.9 10.6 11.2 74.4 86.8 40.7 44.6 74.9 91.1 38.5 36.4
the increased BMC values at the lumbar spine and
the right leg in one of the exposed children were
sustained even throughout period II (Figures 2 and
3). The sustained effect is in line with Gunter et al.
(12). The densitometry results varied a lot between
the right and the left leg in the children in both peri-
ods. Herman et al. (14) showed that the weight bear-
ing, measured with electronic load-measuring
footplates, differs greatly in children with severe CP
when standing. We chose to draw attention to the left
and right legs from the BMC measurement as a
region of interest, since most fractures occur in the
legs in this group of children (16).
Poor nutritional status and GH defi ciency infl u-
ences bone mass and linear growth negatively. Chil-
dren in this study had low IGF-I values for their age
in all but one case (the only child with gastrostomy),
indicating poor nutritional status or insuffi cient GH
secretion. It is important to take nutrition into con-
sideration when planning for training and exercise in
children with severe CP, so that energy intake matches
energy consumption. Exercise on the vibrating plat-
form did not seem to affect weight, lean body mass
or total body mass negatively (Table III).
To give the children the opportunity to be more
active and enjoy the exposure to vibration, three
more activities (raising and lowering, rotation and
sound) were available when the children chose to
press those buttons. The educationalists Lev Vygotskij
(1896 – 1934) and Jean Piaget (1898 – 1980) recog-
nized the need for children to be subjected to prob-
lems that stimulated cognitive development through
acts of cause and effect (32). Standing on this plat-
form, the children ’ s action through the pressing of
buttons creates consequences that are obvious to the
child as the movements (vibration, jumps and rota-
tion) are felt in their own bodies. This may cause a
cognitive effect and may contribute to increased
arousal.
In the present study, DXA measurements are per-
formed. We chose to calculate change in BMC (g)
instead of BMD (g/cm
2 ) since children are expected
to grow during the 3 years of the study. In DXA, the
software calculates the area of bone and the calcium
content in every pixel simultaneously. The sum of
calcium in all pixels within the bone area is the BMC,
expressed in unit grams. Thereafter, the software
divides BMC with the bone area to obtain BMD. As
growing bone increases in strength due to increased
size even if the density in each pixel might be stable,
we think the total amount of bone is a better repre-
sentative of increased strength. It is often seen in
children in periods of growth that BMD is stable
while BMC increases (33; Table IV).There is a pos-
sibility that jumps and rotation added to vibration
might also have infl uenced BMC. As the additional
movements were very subtle, with no hard stops or
sharp turns, the chance of an added effect was con-
sidered minimal. The amount of time that the chil-
dren chose to press the vibration button in period I
(medians of 12 and 13 min/occasion) and the fact
that the children stood the set amount of time (a
median of 10 min) in period II, indicates that the
children enjoyed the exposure to vibration (Table II).
Table IV. Values of bone mineral density (g/cm
2 ) at the lumbar spine, the entire right leg and the entire left leg before and after periods
of exposure of vibration and periods of control in each child.
Lumbar spine
exposure
Lumbar spine
control
Right leg
exposure
Right leg
control
Left leg
exposure
Left leg
control
Before After Before After Before After Before After Before After Before After
Child 1 0.38 0.45 0.45 0.46 0.57 0.71 0.50 0.49 0.62 0.67 0.47 0.53
Child 2 0.34 0.38 0.43 0.43 0.57 0.62 0.47 0.53 0.57 0.61 0.47 0.53
Child 3 0.36 0.38 0.37 0.36 0.41 0.46 0.61 0.60 0.42 0.43 0.58 0.71
Child 4 0.45 0.48 0.42 0.40 0.56 0.56 0.67 0.69 0.56 0.62 0.66 0.67
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Whole body vibration in children with severe CP 137
Figure 3. Percentage change (%) in bone mineral content (BMC)
at the lumbar spine, the entire left and right leg, between baseline
and the end of period II in each child exposed or non-exposed to
whole body vibration.
Table V. Number of occasions/month and minutes of vibrations/
occasion, presented as median (and range).
Occasions/month Minutes/occasion
Months of
no use
Child 1 2.5 (1 – 5) 12 (3 – 14) May
Child 2 2.5 (1 – 6) 13 (6 – 23) October
Child 3 7 (4 – 10) 10 (6 – 10) July, August
Child 4 6 (1 – 12) 10 (9 – 10) July
The platform was used from February – March to December.
Months when children did not use the platform are shown.
Figure 2. Percentage change (%) in bone mineral content (BMC)
at the lumbar spine, the entire left and right leg, between baseline
and the end of period I in each child exposed or non-exposed to
whole body vibration.
In a study by Ward et al. (23) compliance to WBV
treatment was only 44%. In that study, the children
could not infl uence the platform activity.
The platform and study design developed between
the two periods. In period I, the children were free to
vary the frequency of the vibration between 20 and 64
Hz and were allowed a standing time of up to 20 min.
This design led to fewer occasions/week in period I
and a more diverse result on BMC (Figure 2). The
children in period II used the platform in a more
structured way, as the personnel were urged to put the
children in the platform two or three times a week.
The vibration frequency was set to 50 Hz, and the
time to 10 min per session (Figure 3). BMC increased
more regularly during the second period and the dif-
ferent results during this period compared with the
previous indicate that WBV treatment may be more
effi cient when used two or three times/week, 10 min/
occasion, which is in line with Chad et al. (34).
In a review, Rubin et al. (35) point out a great
potential for WBV as a non-pharmacological interven-
tion for osteoporosis, given that the deformations that
result from these low-level vibrations are far below
those that may cause damage to the bone. The use of
WBV as a treatment to prevent osteoporosis in chil-
dren with CP has been discussed in several studies
(15,22 – 24). The measures and terms used in research
concerning WBV devices vary greatly, with vertically
oscillating vibrations reported sometimes as G and
sometimes as Hz (23), tilting vibrations reported as
ground reaction force ⫽ tilt angle ⫻ body mass ⫻ 9.81
kg/ms
2 (23), side-to-side alternating vertical sinusoi-
dal vibrations reported around the fulcrum in the mid-
section of the plate, peak-to-peak displacements
increasing from 2, to 4, and up to 6 mm, and frequen-
cies from 12 to 18 Hz (25). This makes it diffi cult to
compare results between studies. Lorenzen et al. (36)
recommend the consistent, standard use of peak-to-
peak displacement (mm), frequency (Hz) and maxi-
mum acceleration (m/s
2 ) in studies describing
vibrations as in this study. However, when a human
being is placed on the platform, variables including
body size and weight, the placement of the weight,
movement, etc. will infl uence the effects of the vibra-
tions on the bone mass (37). The vibrations will be
dampened as they move through the body, so presum-
ably children who are smaller and thinner will get a
higher dose of a set vibration than would heavier
adults (38). These factors make it diffi cult to calculate
the vibration dose each individual body receives.
Conclusion
The children expressed feelings of contentment while
using the platform and seemed to enjoy the exercise.
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138 Y. Dalén et al.
No negative effects were reported. The platform
might therefore be used as a non-invasive and enjoy-
able method to increase bone mass in children with
severe CP, but larger studies are needed to confi rm
these fi ndings.
Acknowledgements
The authors would like to thank the children, parents
and personnel at Reimers Preschool and Joriel
School, both of which have a programme for special
needs education. Many thanks also go to Ylva Jons-
son, Lena Berglund and Anette Fagler at Karolinska
Hospital, for doing the DXA measurements, as well
as to the nurses at Q62 at Astrid Lindgrens Chil-
dren ’ s Hospital, in Stockholm, Sweden.
This project was funded by ALMI Stockholm
AB, the City of Stockholm Inventors Award, Norr-
backa-Eugenia Foundation administered by Swedish
Institute of Assistive Technology, Arts in Hospital
and Care as Culture, and the Agne Johansson Memo-
rial Foundation. The prototype of the platform was
built by the Royal Institute for Technology (KTH)
and L ö fgren Engineering AB.
Confl ict of interest statement
One of the authors (Y.D.) has Swedish, European
and US patents for the platform. For this reason, Y.D.
did not perform any measurements or tests. No other
author has a confl ict of interest in this study. The
sponsors had no involvement in this study other than
funding.
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