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BACKGROUND
In clinical practice working as a physiotherapist among children with
disabilities, I experienced a non-violent fracture in a child with severe
cerebral palsy (CP). That experience made me aware of the fact that these
children can develop a fragile skeleton over time, partly due to disuse,
because children with severe CP cannot attain an upright position or run
and jump like other children. A standing shell is commonly used in Sweden
to allow children with severe CP to attain an upright position. One aim of
this is to prevent osteoporosis, and the recommended time in the standing
shell is one to two hours daily. This recommended time is often hard to
achieve in clinical practice, because even though the children often like to be
in an upright position, they seldom want to stand strapped in a standing shell
for such a long time. Through additional studies in special pedagogy I
learned the importance of giving the children an opportunity to influence
their own activity and increase their cognitive development through action,
especially through acts that demonstrate cause and effect. I found no studies
to support the hypothesis that standing in a standing shell for one or two
hours would increase bone density, and I wanted to find out whether it
would. I also wanted to make standing in a standing shell more effective and
enjoyable for the children.
1
INTRODUCTION
Physical activity and movement, the importance of which have been
recognized since before the time of Aristotle (384–322 BCE), are greatly
restricted in children with severe CP; this in turn limits these children’s
abilities to interact with their environment. Interaction with the environment
was first elaborated by Plato (427–347 BCE) as the primary cause of
development in the child. Plato conceptualized the child as an inquiring
explorer whose motivation for learning and development was primarily
internal. The educationalists Lev Vygotskij (1896–1934) and Jean Piaget
(1898–1980) agreed with this view. Piaget (Wadsworth, 2004) wrote, ‘It is
obvious that the teacher as organizer remains indispensable in order to create
the situations and construct the initial devices which present useful problems
to the child’; these problems, he theorized, fuel the processes of invention or
construction which occur inside the mind of the individual. In addition to
having restricted movement, many children with severe CP cannot express
themselves through speech. According to Wadsworth (2004), although
language contributes to intellectual advancement, it is not absolutely
necessary, and action is another way to achieve a higher intellectual level.
Children with severe CP need more and better opportunities to be active and
to explore cause and effect in order to improve and expand their cognitive
development. Independent transfer has been considered the most important
factor in communication skills and cognitive development (Granlund and
Olsson, 1988). Spasticity in different forms and weak muscles may prevent
normal voluntary movements and may also lead to deficient postural control,
making it difficult for the children to attain an upright position and dynamic
weight-bearing on the skeleton. Lack of dynamic weight-bearing and
insufficient nutrition are two important factors that make children with
severe CP prone to fractures, some of which occur spontaneously as a result
of fragile bones (Stevenson et al., 2006, Maruyama et al., 2010). The
importance of weight-bearing for the skeleton is shown by the postnatal
adaptation of the skeleton to the environment outside the womb, in which
the femoral diaphysis decreases volumetrically by about 30% during the first
six months, probably because the baby is no longer kicking the inside of the
uterus and thus no longer engaging in frequent ‘resistant training’ (Rauch
and Schoenau, 2001).
2
CEREBRAL PALSY
CP is the most common cause of severe physical disability in childhood, and
the prevalence of CP in the western world is reported to be between 2 to 3
per 1000 live births (Surveillance of Cerebral Palsy in Europe (SCPE),
2000). CP is defined as ‘a group of permanent, but not unchanging, disorders
of movement and/or posture and of motor function, which are due to a nonprogressive interference, lesion, or abnormality of the developing/immature
brain’ (SCPE 2000). CP is caused by a lesion in the brain right before,
during, or right after the birth. Depending on the origin of the lesion,
whether the origin is the basal ganglia, cerebellum, cerebral cortex,
brainstem, or descending spinal tracts, the symptoms of the consequential
motor disorder vary greatly.
The Gross Motor Function Classification System (GMFCS) is commonly
used in clinical practice to assess motor function and classify children
accordingly (Palisano et al., 1997). It is a classification derived from the
Gross Motor Function Measurement (GMFM), a clinical measure designed
to evaluate change in gross motor function in children with CP, developed
by Palisano et al. (1997). GMFCS was tested for reliability and stability over
time by Wood and Rosenbaum (2000). They found that GMFCS can validly
predict motor function for children with CP. GMFCS uses a 5-level scale,
with levels I (least severe) to V (most severe), that classifies the gross motor
function of children and youth with CP on the basis of their self-initiated
movement, with particular emphasis on sitting, walking, and wheeled
mobility. The purpose of GMFCS is to classify a child’s present gross motor
function, not to judge quality of movement or potential for improvement. It
describes the need for use of assistive devices and how the child functions in
his regular environment (Palisano et al., 1997).
SPASTICITY
Spasticity is a common feature of CP, more prevalent in more severe forms
of CP, which can be increased by anxiety, emotional state, pain, surface
contact, or other sensory input.
Spasticity is hypertonia in which one or both of the following signs are
present:
 Resistance to externally imposed movement increases with
increasing speed of stretch and varies with the direction of joint
movement, and/or
 Resistance to externally imposed movement rises rapidly above a
threshold speed or joint angle (spastic catch). (Sanger et al., 2003).
3
Spasticity is complex; children with CP often have a combination of
multiple symptoms and clinical signs that contribute to their disability, so
there is a need for definitions that take a broader perspective. Sanger et al.
(2003), contributed with additional definitions that were developed at the
National Institutes of Health in April 2001:
Dystonia: A movement disorder in which involuntary sustained or
intermittent muscle contractions cause twisting and repetitive
movements, abnormal postures or both.
Rigidity: Hypertonia in which all of the following are true:
 The resistance to externally imposed joint movement is present at
very low speeds of movement, does not depend on imposed speed
and does not exhibit a speed or angle threshold
 Simultaneous co-contraction of agonists and antagonists may occur
and this is reflected in an immediate resistance to a reversal of the
direction of movement about a joint
 The limb does not tend to return toward a particular fixed posture or
extreme joint angle
 Voluntary activity in distant muscle groups does not lead to
involuntary movements about the rigid joints, although rigidity may
worsen.
Because the variety of symptoms differs from child to child, clinical
assessment of spasticity is difficult to standardize. The Modified Ashworth
Scale (MAS) is commonly used in clinical practice to assess spasticity
(Peacock and Staudt, 1991). It grades the resistance encountered in a specific
muscle group by means of passively moving one limb of a child in supine
position through its range of motion at a non-specified velocity. The MAS
scores are as follows: 0 = hypotonic, less than normal muscle tone, floppy; 1
= normal, no increase in muscle tone; 2 = mild, slight increase in tone,
‘catch’ in limb movement, or minimal resistance to movement through less
than half the range; 3 = moderate, more marked increase in tone through
most of the range of motion, but affected part is easily moved; 4 = severe,
considerable increase in tone, passive movement difficult; 5 = extreme,
affected part rigid in flexion or extension (Peacock and Staudt, 1991). The
MAS was found to be reliable by Ghotbi et al. (2009). To decrease
spasticity, injections with Botulinum toxin in spastic muscles and intrathecal
Baclofen are frequently used. The Botulinum toxin distributions need to be
repeated every 3–6 months.
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HIP DISLOCATION
The hip joint consists of the head of the femur and the acetabular roof of the
pelvis. When the head of the femur migrates in a lateral direction out of the
socket, it is called hip subluxation. A manifest luxation is considered present
when the migration exceeds 80% (Eklöf et al., 1988). Hip X-ray and
assessment of the hip migration index (MI) (Reimers, 1980) are common in
clinical practice and reported to be sufficient in screening for dislocation in
children with CP (Fig. 1). An MI up to 16% in children under four years of
age and an MI up to 24% in children 12 years of age or over is considered
normal; higher figures represent subluxation. An MI of 33% is the cut-off
point for initiating treatment in Sweden (Hägglund et al., 2007a). This means
that 33% of the caput femoris is not covered by the acetabular roof of the
pelvis. Acetabular index (AI) is another common index used to assess hip
dislocation (Fig. 1). Since lateral dislocation of the femoral head is common
without acetabular dysplasia and since acetabular dysplasia occurs later than
the lateral dislocation, MI seems to be the most useful measurement when
evaluating hip dislocation in children with CP (Hägglund et al., 2007a).
Fig.1. Measurement of acetabular index (AI) and migration index (MI=A/B × 100).
Published with permission from the Swedish National Health Care Quality Program
for prevention of hip dislocation and severe contractures in cerebral palsy (CPUP).
Children with CP are born with a normal hip joint, but the natural history of
hip development showed that 46% of children not walking independently
had one or both hips subluxated or had treatment for their hips by the age of
five years (Scrutton et al., 2001). Hip dislocation can start when children are
as young as two years of age and is reported more severe for children in
GMFCS V. The risk for an MI over 40% has been reported in 64% of
children classified as GMFCS V (Hägglund et al., 2007b).
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OSTEOPOROSIS
Bone is living tissue that adjusts to its environment. There are three major
cell types that provide adaptation through bone turnover: osteoblasts (form
bone), osteoclasts (resorb bone), and osteocytes (load sensitive
‘mechanostats’). Bone cells react to the hormonal and nutritional situation
and also to mechanical loading/weight bearing. Bone also consists of two
different macroscopic tissues: trabecular bone (the vertebrae) and cortical
bone (the long bones). The human body consists of up to 20% trabecular
bone, where turnover is faster and thus more quickly influenced by
hormones, for example in the vertebrae. Rubin et al. (2006) showed in sheep
that cortical bone, for example the long bones of the legs, are influenced by
mechanical stimuli such as vibration (Fig. 2).
The natural history of gain in bone mineral density (BMD) in children with
CP is important to understand when discussing changes in BMD over time.
A prospective study over two to three years with 69 subjects with CP
concluded that children with severe CP developed osteoporosis over the
course of their lives. They did not lose bone mineral, but compared to agematched children without disabilities (z-score), BMD increased much less
(Henderson et al., 2005).
Fig.2. Three-dimensional reconstructions of trabecular bone from the distal femur in
control sheep (left) as compared with the same region of experimental sheep (right),
which had been subjected to vibrations for 20 minutes/day of a low-level (0.3G),
high-frequency (30 Hz) mechanical signal. The experimental bones have improved
connectivity and enhanced bone volume fraction, and they are stiffer and stronger
than the control bone. Printed with permission from the author (Rubin et al., 2006).
6
Children with CP are born with a normal skeleton, but as they grow older
and are unable to walk, run, and jump like other children, the skeleton turns
fragile and the risk for fractures increases (Henderson et al., 2002, Stevenson
et al., 2006). Spasticity also induces mechanical forces on the proximal
femur, which can give rise to bone deformities such as acetabular
malformations that facilitate hip dislocation (Shefelbine and Carter, 2004).
Many of the children who sustain a fracture will sustain repeated fractures,
most commonly in the femur (Henderson 1997, Presedo et al., 2007,
Maruyama et al., 2010). The reason for the fracture is sometimes unknown;
fractures can occur spontaneously, contributing to great pain and suffering,
and the fracture diagnosis is often delayed (Presedo et al., 2007, Maruyama
et al., 2010). The risk of fracture is reported highest in non-ambulatory
children with anticonvulsant medication, lower triceps skinfold z-score, and
a prior history of fracture (Henderson et al., 2002, Presedo et al., 2007).
The diagnoses Osteoporosis in children and adolescents requires the
presence of both a clinically significant fracture history and low bone
mineral content (BMC) g or BMD g/cm2 according to Rauch et al. (2008).
Rauch et al. (2008) also recommended that the diagnosis should not be made
on the basis of densitometry criteria alone, as in the adult population, and
further define osteoporosis as:
A clinically significant fracture history is one or more of the following:
 Long bone fracture of the lower extremities
 Vertebral compression fracture
 Two or more long-bone fractures of the upper extremities
 Low BMC or BMD is defined as a BMC or areal BMD z-score that
is less than or equal to -2.0, adjusted for age, gender and body size,
as appropriate (Rauch et al., 2008).
Due to the increased risk of fractures in children who lack dynamic weightbearing on their skeleton, measurements of bone mass in children are
becoming more frequent.
Dual-energy X-ray absorptiometry (DEXA) is the most commonly
employed technique for bone mass determinations. The radiation dose is
low, and precision and accuracy are high. Body composition, BMD, and
BMC can all be derived from DEXA. BMC is considered better to use for
prospective measurements in children, since growth of the skeleton is taken
under consideration. Because the beam in BMD measurements needs to pass
further through large bone, it can falsely seem to indicate higher bone
density in the large bone. The effect can be illustrated by two different-sized
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bottles placed in the sunshine: the larger bottle will cast a darker shadow
even if the two bottles contain the same amount of liquid (Rauch and
Schoenau, 2001). Lately, there have been discussions about whether or not
BMD measurements by DEXA are accurate and reliable in trabecular bone,
considering the presence of both absorptiometrically disparate intra-osseous
bone marrow and the extra-osseous mixture of fat and lean soft tissues. In
cortical bone, the measurements would seem to be more reliable (Bolotin,
2007).
PREVENTION and TREATMENT OF OSTEOPOROSIS IN CP
Nutrition
Children with severe CP have difficulty eating and swallowing, mostly due
to abnormal muscle tone. It is therefore often difficult for them to consume
sufficient nutrients, and malnourishment and growth failure are common in
children with severe CP (Thommessen, 1991). This is more an effect of the
low quantity of food they are able to ingest, rather than the quality of food
they eat (Sullivan et al., 2002). Analysis of insulin-like growth factor-I (IGFI) levels in the blood can indicate whether a child has a sufficient nutrition.
Circulating IGF-I is mainly produced in the liver, and normal levels depend
on both nutrition and growth hormone secretion (Thissen et al., 1999).
Individual nutritional assessment and management is important in the overall
care of children with CP.
Orthopaedic interventions
Orthopaedic interventions aim at improving the functional ability of the
child, and include surgery and orthotic devices. Surgical preventive actions
include muscle prolongation, selective dorsal rhizotomy, and osteotomies,
however, the reoperation rate can be over 50% in children with severe CP
(Shefelbine and Carter, 2004).
Pharmacologic interventions
In Sweden, to our knowledge, pharmaceuticals to increase bone density are
not used for children with severe CP; there are, however, reports from other
countries about the effect of osteoporosis-specific drugs in children with CP
(Bachrach et al., 2010).
Physiotherapy
Physiotherapy aims to prevent impairment and activity limitation. Postural
management equipment and orthotics are often used for positioning in
standing, sitting, and lying, to encourage active movement, maintain muscle
8
length, control or prevent deformity, and increase function. The sorts of
aerobic exercise that create cardiovascular and musculoskeletal fitness in
other children cannot be offered to children with severe CP. Creating
methods to make physical activity available to children with severe
disabilities is a challenge for the future and is in line with Articles 6, 23, and
24 of the United Nations’ Convention on the Rights of the Child (1989).
In the 1980s a multidisciplinary team consisting of a physiotherapist, an
orthopaedic surgeon, and orthopaedic engineers in Uppsala, Sweden,
developed a standing shell (Fig. 3) to allow children with severe disabilities
to be placed in a maintainable upright position. It is mainly prescribed by
orthopaedic surgeons, often on the request of a physiotherapist. The aim of
the standing shell is to create the optimal alignment of body segments in the
individual child:
 to allow weight-bearing in an upright position in order to increase
bone density and prevent hip dislocation and contractures
 to vary the body position, and
 to facilitate postural control in children with severe disabilities
(Ölund, 2003).
A unique standing shell for the individual child is produced by orthopaedic
engineers in an orthopaedic workshop. Symptoms in children with severe CP
vary greatly by type and severity, so the orthopaedic engineer starts by
noting the child’s contractures and spasticity. After that, a plaster cast is
formed around the legs and back of the child. A sheet of polyethylene
plastic, 4 mm to 10 mm thick depending on the need for stability, is then
heated, formed, and adjusted to the cast. The orthopaedic engineer then
manually evaluates the child’s weight-bearing in the standing shell in order
to make adjustments and add the necessary fittings for optimal alignment
and weight-bearing. The standing shell is fastened in front with straps. As
the child grows, the legs of the standing shell are commonly lengthened and
a complete new standing shell is needed about once a year as long as the
child grows. In addition to any orthopaedic results, the standing shell
provides the child with access to dining and work tables, eye contact with
peers, and a variety of social and personal benefits.
9
a.
b.
c.
Fig.3. Three individually moulded standing shells shown from different angles: from
posterior position (a and c) and from lateral position (b). One standing shell (c)
includes a neck support. Handles to be used by caregivers when moving the child in
the standing shell are shown in pictures a and c. The black bars between the legs
secure stability. Decorative patterns on the standing shell are chosen by the child
and/or the parents.
The recommended standing time varies from one to two hours (Ölund,
2003). There is no published study to our knowledge exploring whether time
spent in the standing shell has an effect on bone mass or hip dislocation.
Children seem to enjoy the upright position, but for many children being
strapped in a standing shell for up to two hours per day may be a difficult
goal to achieve.
VIBRATION
Weight-bearing is static in a person standing still, but becomes dynamic with
the addition of a force (as in jumping), measurable by Newtons (N; 1 N =
the power required to accelerate a mass of 1 kg by 1 m/s2). Whole body
vibration (WBV) can cause dynamic weight-bearing in the skeleton of a
standing subject.
Vibration is the rapid linear motion of a particle or of an elastic solid about
an equilibrium position.
Frequency refers to the number of cycles (or waves) that a vibrating object
completes in one second. The unit of frequency is hertz (Hz). A complete
cycle of vibration occurs when the object moves from one extreme position
to the other extreme (peak-to-peak).
Amplitude is the maximum excursion of the wave from the zero or
equilibrium point. The intensity of vibration depends on its amplitude.
10
Peak-to-peak displacement is the distance from a negative peak to a positive
peak. If the waveform is symmetrical, the value is exactly twice the value of
the peak amplitude (Fig.4).
Amplitude
Peak-to-peak displacement
Time
Fig.4. One cycle of vibration. Amplitude and peak-to-peak displacement are shown.
The speed or velocity of a vibrating object varies from zero to maximum
during each cycle of vibration. It moves fastest as it passes through its
natural stationary (zero) position to an extreme position. The vibrating object
slows down as it approaches the extreme, where it stops, and then moves in
the opposite direction, through the stationary position toward the other
extreme. Speed of vibration is expressed in units of metres per second (m/s).
Acceleration is a measure of how quickly speed changes with time. The unit
of acceleration is metres per second squared (m/s2). A heavy object standing
on a vibrating platform will have smaller accelerations compared to a lighter
object since its amplitude will be smaller due to its heavier weight. If the
motors have constant amplitude, the acceleration will increase with weight.
Gravity and Gravitational force (G) are similar concepts that could lead to
confusion. Gravity describes the attractive force that exists between earth or
any celestial body and any object. The unit G describes the acceleration
imposed on a person during occasions of dynamic weight-bearing such as
vibrations or acceleration. One G equals 9.81m/s2.
Root Mean Square amplitude (RMS) is the square root of the average of the
squared values of the waveform. In the case of the sine wave, the RMS value
11
is 0.707 times the peak value. RMS values are important when discussing
power or energy imposed on a human standing on a vibrating platform since
it reflects the mean power of platform acceleration.
There are many ways to describe vibrations in research and the descriptions
are inconsistent among different studies of WBV exercise. Lorenzen et al.
(2009) propose that a standardized terminology including peak-to-peak
displacement (mm), frequency (Hz), maximum acceleration (m/s2), and how
the maximum acceleration was determined should be used in future WBV
research to allow between-study comparisons.
THE VIBRATING PLATFORM
To motivate the children in the standing shell, give them a tool to explore
cause and effect, and make dynamic loading enjoyable, a vibration platform
with additional functions was constructed (Fig. 5). The child in a standing
shell was placed on the platform and securely fastened. At the touch of
colourful buttons, the child could induce vibrations, raising and lowering,
and 90-degree turns to the left and right. The platform remained stationary
unless the child pressed the buttons.
Fig.5. The vibrating platform with a standing shell.
Frequency-weighted acceleration measures vibration accelerations at
different frequencies to correspond to human vibration sensitivity and is used
to calculate the vibration dose imposed on the individual human body.
Because vibration dose is dependent on the weight of the user, to ensure that
the vibration dose for children using the platform was within the limits of the
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European directives, two girls without disabilities, both aged eight years, the
first weighing 26.5 kg and the second 37.5 kg, used the platform with a
frequency of 50 Hz for ten minutes. The frequency-weighted acceleration
dose measured with HealthVib (CVK AB, Aurorum Science Park 1C, Luleå,
Sweden) after 10 minutes was 1.71 m/s2 for the first girl and 1.60 m/s2 for
the second. Converted to an eight-hour period (a working day), the doses
were 0.25 and 0.23 m/s2, well within the limit of 0.50 m/s2 set by EU
directive 2002/44/EG and SS-ISO 2631-1 (see Table 1 and Appendix).
Permission was given by the parents of the girls.
Table 1. Maximal acceleration measured as gravitation force (G), metre/second
squared (m/s2), and root mean square (RMS) of the amplitude value over time
in the platform when unloaded.
Frequency
64
50
40
30
20
m/s2
29.4
23.5
20.1
9.8
4.4
G
3.0
2.4
2.1
1.0
0.5
RMS
1.2
1.0
0.6
0.3
0.1
To assess the figures in Table 1, the Vibro Scanner (NetterVibration,
Fritz-Ullmann-Straße 9, 55252 Mainz-Kastel, Germany) was used.
The new vibrating platform was intended to give the children an opportunity
to promote their bone density while playing and having fun. However, it was
not known whether use of the vibrating platform would influence BMC or
hip dislocation in children with severe CP or whether the children would
tolerate the generated movements and sounds.
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AIMS
The aims of this thesis were to evaluate the effects on bone mass and hip
dislocation in children with severe CP when standing in a standing shell with
and without vibration and to assess the reactions shown by the children
when using the vibrating platform.
METHODS
DESIGN
Study I was a cross-sectional, descriptive study.
Study II was a descriptive, experimental longitudinal study.
PARTICIPANTS
In Study I, 17 families of children diagnosed with severe CP responded to an
appeal on the website of the National Association for Disabled Children and
Youths, and five families were recruited from habilitation centres in the
Stockholm area. All 22 families agreed to participate. Two families
withdrew before the start of the study because of mental stress, one teenager
dropped out, and the parents of one child withdrew because of reluctance
regarding the use of sedation. Eighteen children (11 boys and 7 girls) with
severe CP, median age 10.5 (range 3–18) years participated in Study I. Three
of the children scored GMFCS IV and 15 scored GMFCS V.
In Study II, the parents of five children with severe CP, four boys and one
girl, responded to another appeal on the website above. The girl withdrew
after the first session of measurements because of mental stress associated
with the child’s dysfunctions. For anthropometrics of the participants in
Studies I and II, see Table 2. Variables assessed in the studies are shown in
Table 3.
Table 2. Anthropometrics of the participants in Study I and II. Number of participants
(n), age (years), height (m) in standard deviation scores (Height SDS), body mass
index (kg/m2) in standard deviation scores (BMI SDS), and insulin-like growth factor
I (µg/L) in standard deviation scores (IGF-I SDS). The four participants in Study II
were included in both Study I and Study II. Figures presented are median (range).
Study
I
Participants
(n)
18
II
4
Age
(years)
10.5
(3–18)
4.0
(4–6)
Height SDS
(m)
-2.55
(-4.62 to -0.55)
-1.40
(-2.6 to -0.8 )
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BMI SDS
(kg/m2)
-0.5
(-3.0 to 1.5)
-2.0
(-3.0 to 1.0 )
IGF-I SDS
(µg/L)
-1.73
(-2.68 to 1.53)
-0.42
(-0.97 to 1.64)
Table 3. Variables assessed in Study I and Study II. Height, weight, bone
mineral density (BMD), spasticity, bone mineral content (BMC), hip
migration index (MI), insulin-like growth factor-I (IGF-I), time in
the standing shell, time of exposure to whole body vibration (WBV), and
interpretation of facial expression (facial expression).
Height, weight
Spasticity
BMD
BMC
MI
IGF-I
Time in standing shell
Time of WBV
Facial expression
Study I
●
●
●
●
●
●
Study II
●
●
●
●
●
●
In Study I, time in the standing shell was recorded by parents and
schoolteachers, who filled in a time protocol to record the numbers of
minutes per day the children used their standing shell. The protocol was
recorded twice, one week at a time, with a break of two weeks.
Anthropometric measurements were performed, through which Body Mass
Index (BMI) kg/m2 was calculated. The areal BMD (g/cm2) was assessed
using DEXA on a Hologic 4500 densitometer (Hologic, Waltham, MA) for
subtotal (head excluded) whole body and for the lumbar spine. Both hips of
all children were X-rayed within three months of the BMD measurements.
Femur head position and MI were calculated to evaluate the degree of hip
dislocation (Reimers, 1980). Spasticity was assessed with MAS according to
Peacock and Staudt (1991). The hip flexors and adductors were assessed by
each child’s regular physiotherapist, and assessment results were obtained
from the children’s medical files. The children were categorized into two
groups: non-spastic MAS 0–1 (n = 7) and spastic MAS 2–4 (n = 11). Two
children, who according to the medical files were spastic, were not assessed
because of pain and were included in MAS 2–4. Eight children, two of
whom were classified as spastic, had IGF-I levels 2 SD below the agematched mean, indicating poor nutritional status.
In Study II, four children (also included in Study I), median age 4 (range 4–
6) years, all GMFCS V, participated. Anthropometric measurements were
performed, through which BMI was calculated. Analysis of IGF-I in the
blood was assessed. BMC was assessed using DEXA on a Hologic 4500
densitometer (Hologic, Waltham, MA) for subtotal (head excluded) whole
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body and for the lumbar spine. Both hips of all children were X-rayed within
three months of the DEXA measurements. Femur head position and MI were
calculated to evaluate the degree of hip dislocation (Reimers, 1980). The
children in Study II were included in the CPUP-program (Swedish National
Health Care Quality Program for prevention of hip dislocation and severe
contractures in cerebral palsy) and treated with Botulinum toxin in order to
prevent hip dislocation, thus, spasticity was not assessed.
Study II was divided into period I and period II, with a washout period of
one year between the periods.
Period I
Child 1 and child 2 used the platform for eight or nine months while child 3
and child 4 were controls. The platform was used at the children’s school. No
instruction was given as to how often each child was to be placed in the
platform. The platform was used at the convenience of the personnel and the
child. The children could choose to vibrate at a continuous variable
frequency range of 20–64 Hz. Direct, vertical vibrations were used. Because
the children needed to stand with straight legs, the peak-to-peak
displacement of the vibrations was low (0.3 mm when un-loaded). A
computer registered the length of time vibration was used in each session.
Period II
Child 3 and child 4 used the platform for eight or nine months, with child 1
and child 2 as controls. The platform was used at the children’s school.
During this period, the personnel were instructed to put the children in the
platform two to three times a week. The children were not in control of the
vibration as opposed to period I, but could choose to use the other functions
as they wished. The peak-to-peak displacement of the vibrations was the
same as in period I (0.3 mm when un-loaded). The vibration was set to 10
minutes by a stopwatch and the frequency was set to 50 Hz.
In both periods parents and personnel observed the child when using the
platform and interpreted the feelings shown by the child’s facial expressions.
The studies were approved by the ethics committees at Karolinska
University Hospital and Huddinge University Hospital and the Radiation
Protection Committee at Karolinska Hospital, Stockholm, Sweden. The
Swedish Medical Products Agency was informed of Study II.
16
STATISTICS
In Study I the results are presented as median (range) if not otherwise
indicated. Pearson’s correlation was evaluated according to Domholdt, 2005:
very high, r = 0.90–1.00; high, r = 0.70–0.89; moderate, r = 0.50–0.69; low,
r = 0.26–0.49; and little, if any, r = 0.00–0.25. Path analysis techniques were
used to examine the direct and indirect effects between variables. These
techniques are especially appropriate when theoretical, empirical, and
commonsense knowledge of a problem provides a defensible mapping of the
latent variables present and of their probable causal links. Standardized
regression coefficients (beta weights) make it possible to compare variables
and explore the importance of an independent variable versus a dependent
variable while controlling for other variables.
In Study II data are presented as median (range). Data were not statistically
analysed due to the few participants.
17
RESULTS
STUDY I
The standing shell was used a median of 40 (range 4–164) min/day. Fifteen
children stood once a day during the school week; three children stood twice
a day. Children classified as spastic (n = 11) had a standing time of 38 (4–
164) min/day. Children classified as non-spastic (n = 7) had a standing time
of 49 (8–86) min/day. Age-matched BMD in the lumbar spine was 73% (58–
93%). Three children had sustained four fractures. Hip X-rays showed an MI
of 28% (0–52%) in the most dislocated hip and of 14% (0–31%) in the least
dislocated hip. Children assessed as spastic showed an MI of 31% (11–52%)
in the most dislocated hip at age 7. Children assessed as non-spastic showed
an MI of 12% (0–28%) in the most dislocated hip at age 11. Standing time
showed little if any correlation with whole body BMD (r = 0.04) and lumbar
spine BMD (r = 0.05). Standing time showed a low correlation with hip
migration (r = 0.42). Spasticity (MAS scores of 2–4) in hip adductors and/or
flexors and standing time had a significant and negative effect on hip
migration. The statistical analysis is based on the correlation matrix below
(Table 4). Statistical analysis of the results is presented in Fig. 6.
Table 4. Pearson correlation coefficients between variables eligible for the structural
equation modeling. Weight (kg), Square root transformed standing time (SQRT,
min/day), whole body and lumbar spine bone mineral density (BMD g/cm2)
and hip migration index (percent), n = 18.
Weight
SQRT
Whole body BMD
Lumbar spine BMD
Hip migration
Weight
(kg)
SQRT
(min/day)
1
-0.17
0.49
0.86
-0.56
1
0.04
0.05
0.42
18
Whole
body
BMD
(g/cm2)
Lumbar
spine
BMD
(g/cm2)
1
0.57
0.01
1
-0.41
Hip
migration
%
1
Fig. 6. The model best fit to data. Path coefficients (standardized regression weights)
are presented between the variables hip dislocation (migration percent), spasticity
(MAS 2–4), time spent in the standing shell (square root transformation, SQRT
standing time), and weight (kg). The arrows show how the variables influence each
other. Spasticity and standing time increased hip dislocation. Spasticity decreased
weight. Statistically significant figures are in bold.
STUDY II
Between period I and period II the DEXA measurement equipment was
upgraded and the digital detectors and software were replaced. This
increased the sensitivity to areas of low bone mass and the detected values
changed significantly as larger areas of bone were included. This had a
profound effect on absolute values in measurements of children with
extremely low values. Thus, the absolute values could not be compared
between the periods as the measurements before and after the upgrade were
too dissimilar.
In period I, children exposed to vibration did not get Botulinum toxin
injections.
In period II, injections with Botulinum toxin were given to all four children.
The boys in period I were exposed to WBV a median of 2.5 (range 1–6)
occasions/month, 12.5 (range 3–23) minutes/occasion, and showed a median
difference in BMC from baseline to end of period I of 3.1/1.9 g (controls 0.9/0.7 g) in the lumbar spine, -2.3/10.8 g (controls -0.3/3.9 g) in most
loaded leg, and 8.9/-4.3 g (controls -3.2/-5.1 g) in the least loaded leg. Boys
in period II were exposed 6.5 (range 1–12) occasions/month, 10 (6–10)
min/occasion, and corresponding differences in BMC in lumbar spine and
most and least loaded legs for exposed boys (controls) were 1.0/1.3 g
(2.6/0.6 g), 13.0/12.5 g (0.0/-0.7 g), and 13.7/16.3 g(9.9/3.9 g).
In both periods I and II the children’s reactions were positive. No negative
effects were recorded.
19
DISCUSSION
The time spent in the static standing shell was not shown to influence BMD
in children with severe CP, and standing time seemed to have a negative
effect on the hip joint in children with spasticity. When the loading was
dynamic, as in the vibrating platform in Study II, a tendency towards
increased BMC was seen and no negative effect on hip dislocation or
nutritional status was found. This indicates that the vibrating platform may
be a way of increasing bone density that is non-invasive, enjoyable, and
more effective than standing in a standing shell without vibration. The
children expressed feelings of contentment while using the platform; they
seemed to enjoy the motion and to be happy to be ‘in charge’.
Participating children in both studies showed low values in height, BMI, and
IGF-I compared to age-matched children (Table 2). Eight of the 18 children
in Study I had IGF-I levels lower than 2 SD below the age-matched mean,
indicating poor nutritional status, although partial growth hormone
deficiency could not be excluded. Seven of them were classified as spastic.
In Study I, spasticity showed a significant and negative effect on weight
(beta weight correlation coefficient r = -0.47) (Fig.6), indicating that
spasticity could be very energy-consuming besides making food
consumption more difficult. Children with severe CP are often subject to
training regimens. If their intake of food does not compensate for energy
expenditures due to spastic muscles and exercise, the building of bone
density may suffer. In Study I, spasticity significantly influenced an increase
in hip dislocation (r = 0.48) (Fig.6). This is in line with Henderson and
Greene (1995), who found that two of the most important factors for bone
density are weight-bearing and nutrition. Thus the children with severe CP
who have difficulties eating and walking suffer an increased risk for
osteoporosis and hip dislocation. In designing training and nutritional
regimens for children with spastic CP, this may be important to consider. In
Study II, there was a tendency to an increase in IGF-I values after exposure
to vibration; it would be interesting to verify this in larger studies.
In Study I, hip dislocation showed a significant and negative correlation with
time in the standing shell and spasticity. The spastic muscle force may still
affect the children even when they are strapped in a standing shell (Fig. 7).
Shefelbine and Carter (2004) used a finite element model to mimic typical
loading conditions in children with CP. These loading conditions influence
the development of bone that facilitates hip dislocation (Fig. 7). Hip
dislocation is considered to be caused by spastic muscle forces acting on the
femoral head in the acetabular cavity. Those forces may be stronger when
20
the child is strapped and the joints of the knee and pelvis, the two joints
above and under the hip joint, are prevented from moving. The power of the
spastic muscles still working, but unable to move the retrained lever arms of
the legs, may instead be focused on the hip joint, resulting in dislocation of
the hip (Fig. 7). Thus, discomfort may be the reason why children classified
as spastic used the standing shell more than 10 minutes less than did nonspastic children.
Fig.7. The spinal column, pelvis, and femurs with straps over pelvis and knees.
Arrows show the direction of the muscle power imposed on the hip joint while the
knee and pelvis are fixed.
In Study I, little if any correlation (r = 0.04) was found between time in the
standing shell and whole body BMD (Table 4). This finding accords with
Caulton et al. (2004) who reached the conclusion that longer periods of
standing in non-ambulant children improves vertebral but not tibial
volumetric trabecular BMD and is unlikely to reduce the risk of fracture in
the lower limbs, where most fractures occur in children with CP. The
loading of the skeleton may need to be more dynamic than is possible in the
standing shell only. In Study II, WBV was used to create more effective
loading of the skeleton and this showed a tendency to increased BMC in
children exposed to vibration compared to controls. This is in line with Ward
et al. (2004) who performed a randomized controlled study including 20 preor post-pubertal disabled children. The children were randomized to stand on
21
an active vibrating platform (n = 10) or a placebo platform (n = 10) for 10
minutes/day, five days/week for six months. In children who used active
platforms, tibial BMD increased by six percent, and in children on placebo
platforms, tibial BMD decreased by 12%. However, those children were
ambulant and that study used a different design of vibrations. Verschueren et
al. (2004) also showed that WBV may be a feasible and effective way to
promote bone mass, but that study was in postmenopausal women with low
BMD. Stark et al. (2010) recommended a new physiotherapy concept (‘On
Your Feet’) that included WBV and that showed a significant effect on
BMD, muscle force, and gross motor function in children with bilateral
spastic CP. Rubin et al. (2006), found that low-level mechanical signals at
frequencies of 15 Hz to 90 Hz were anabolic and could be used as a form of
passive exercise to positively influence skeletal status, thus the frequency in
Study II was set within this frequency range.
In Study II, period I, the difference in BMC from baseline to end of period
showed four negative values in children with no exposure to vibration, but
only two negative values in exposed children. In period II all four children
showed positive values in BMC when exposed to WBV (See Study II, Fig.
2). In child 1 a decrease in the most loaded leg was shown during exposure
(period I), but an increase in the least loaded leg was sustained throughout
period II. A sustained effect could also be seen in the lumbar spine of child
1. Sustained effect of treatment is consistent with Gunter et al. (2008) and
Warden et al. (2007). Also, Herman et al. (2007), showed that weightbearing during standing, measured with electronic load-measuring
footplates, differs greatly in these children. It would have been interesting to
measure the most and the least loaded leg in each child but, in the present
study parents and personnel were asked separately about each child’s most
and least loaded leg. Thus the information was very subjective and may be
questioned. However, the answers were consistent and the subjective nature
of the information was accounted for.
As discussed above, the use of terminology in WBV research is inconsistent
and Lorenzen et al. (2009) suggested that peak-to-peak displacement (mm),
frequency (Hz), maximum acceleration (m/s2), and method of measuring
maximum acceleration should be used in future research to allow
comparisons between studies. This recommended terminology was used in
Study II, but since it was not used in the studies reported above, cross-study
comparisons of the effects of WBV between them and Study II are not
feasible.
Vibrations may be hazardous to health. Occupational exposure to hand-held
vibrating tools (hand-arm vibration) is often associated with vibration22
induced white fingers. It can cause acute effects on nerves, muscles, heartrate regulation, and changes in peripheral vascular flow for those who, like
bus drivers, for example, sit on vibrating chairs for the entire work day.
(Björ, 2008). Strong vibrations (high amplitudes) may lead to various
damaging effects to the body (e.g. headaches) since inner organs shake along
with the vibration, which could induce a reaction from the autonomic
nervous system and cause heart failure (Björ, 2008). EU directive
2002/44/EG and SS-ISO 2631-1 (see Appendix) elucidate the risks and set
limitations for the dose of WBV exposure. Frequency-weighted
accelerations are used to create limits for WBV exposure on an eight-hour
daily basis. Our initial experiment with two girls (page 12) showed that the
vibration dose of the platform used in Study II was well within the limits set
by the EU directive. The values of the different parameters of the platform
shown in Table 1 were assessed on the unloaded platform. When loaded
with a person standing on the platform, the values would be different and
would give the person an individual WBV-dose depending on that person’s
body composition. The experiment with the two girls shows that although
they are the same age, because they differ in weight by more than 10 kg,
they receive different WBV-doses at the same settings, with the lighter girl
getting a higher dose. This finding is in line with the findings of Harazin and
Grzesik (1998), which showed that the transmission of vibration to different
body segments varies when the body posture and composition alter the
elastic and damping properties of the person. It is important to consider this,
since children with severe CP are often underweight.
The peak-to-peak displacement of the platform used in Study II was 0.3 mm.
This low displacement was chosen because the children were standing in a
standing shell with (almost) straight legs. The risk of vibration transmission
to inner organs and the head is thus lower than in regular devices with
amplitudes of 2 mm to 6 mm where the main intended use is to increase
muscle strength in subjects with knees bent (Abercromby et al., 2007). In
Study II, the intended use of WBV was to affect BMC in the legs, not
muscle strength. A study by Wren et al. (2010) including 31 preteen children
with CP classified as GMFCS I–IV showed that vibrations with a frequency
of 30 Hz and peak acceleration of 0.3 G (compare with Study II where
acceleration was 2.4 G at a frequency of 50 Hz, see Table 1) increased
cortical bone area and the structural properties in the legs, which could lead
to a decreased risk of long bone fractures in some patients. The children
included in that study were able to stand by themselves for 10 minutes in
contrast to the children in Study II who could not stand by themselves at all
without a standing shell. Wren et al. (2010) suggested that children with
more severe CP may benefit even more from vibration treatment than the
children in their study. Compliance in the study by Wren et al. (2010) varied
23
greatly, perhaps due to the lack of opportunities for the children to influence
the treatment (no colourful buttons to push, no additional movements to
choose from, as in the vibrating platform in Study II). Some authors have
found other positive effects of WBV. Ahlborg et al. (2006) showed that
WBV training seems to increase muscle strength in adults with CP, and
Semler et al. (2007) showed that mobility in immobilized children and
adolescents increased after treatment with WBV. Mester et al. (2006)
discussed the possibility that this reaction to WBV may be caused by a
deformation of the blood vessels (round vessels become elliptic) that
increases the total peripheral resistance in the vessels, causing the body to
open more capillaries, dilate more vessels, or both as the gas and material
metabolism between the blood and the muscle fibres improves.
Physiotherapists have used local vibration to decrease spasticity for many
years (Eklund and Steen, 1969, Cannon et al., 1987). We found that muscle
tone in the arms of a boy who was not included in the study seemed to
decrease after a 10-minute session of WBV, as shown in Fig.8.
Fig.8. Photos of a boy with severe cerebral palsy and rigid spasticity show
the muscle tone in the arms before, during, and after a 10 minute session
on the vibrating platform. Printed with permission.
The small and heterogeneous sample of participants in Study I made definite
conclusions difficult to draw. Families of children with severe CP are often
overloaded in their day-to-day lives and may find it hard to participate in
research. This adds to the difficulties of creating large studies in this group
of children. Contractures, difficulty following instructions, and involuntary
movements increased the challenges of using DEXA measurements and
necessitated sedation, which was expensive in terms of time and personnel.
DEXA was chosen in these studies because of its low radiation and cost. The
standing shells include rather large reinforcements to support the feet
(Fig. 3), which may dampen the effects of vibrations and thus the effect on
BMC.
24
CONCLUSION
Time spent in the standing shell alone may not influence bone mineral
density in the legs of children with severe cerebral palsy and may even have
a negative effect on hip dislocation in children with spasticity. Standing in
the standing shell on a platform with whole body vibration may be an
effective and enjoyable method of increasing bone mineral content in
children with severe cerebral palsy.
CLINICAL IMPLICATIONS
General recommendations for time spent in the standing shell, based on
presumptions of increasing bone density or reducing risk of hip dislocations,
could be replaced by individual recommendations adapted to the wishes of
the child. This type of vibrating platform could be a non-invasive treatment
to improve BMC and give children with severe CP a more effective and
enjoyable time in the standing shell.
25
ACKNOWLEDGEMENTS
I wish to express my sincere gratitude to all those who have made this work
possible. In particular, I would like to thank all the children, parents and
personnel who have participated with great endurance and patience.
I would like to thank my supervisors who made me feel confident and safe in
what I was doing.
Brita Klefbeck, my main supervisor. Your calm reassuring voice and your
friendliness was a great comfort to me and your never-ending support made
it possible to complete this work. Thank you for being so patient and
persistent. Your last words were often “kämpa på!” which we both adhered
to!
Eva Mattsson, my supervisor, for sharing your profound knowledge in
research, for your eagle eyes and for your deep kindness. You were a good
base for giving me insight in the limits of statistics too. Thank you for
showing confidence in me.
Maria Sääf, my supervisor for laughing and sharing with me the world of
hormones and bone density and for being open minded and making me
confident in what I was doing.
Yvonne Haglund-Åkerlind, my supervisor for always being so
contagiously positive and always sincere in caring for the children.
Sven Nyrén, my co-author in Study II. It was great to have you by my side
when struggling with statistics and graphs that we never got to use, but we
learnt a lot along the road. You reassured me many times! Thank you.
Personnel at Reimers Preschool and Joriel School, both of which schools
have a program for special needs education. Thank you for so willingly
participating together with the children in the experiment with the vibrating
platform and for the neatly managed recordings!
Jakob Bergström, who guided me through the narrow roads of statistics
and through patient discussions, you even made me understand most of it.
The members of the research group at the Department of NVS, who
gave me good support and great advice to improve my work.
26
Astrid Lindgren´s children´s hospital: To the staff at Q62 who helped
with sedation and transports of the children and to the staff at the lab for
professional care of the children when taking blood samples.
Ylva Jonsson, Lena Berglund, and Anette Fagler at Karolinska
Hospital, for giving us all the time we needed, for showing love and
understanding for me and the children when performing the DEXA
measurements.
Sven Löfgren, Löfgren engineering AB, for gladly assisting me with
vibration measurements and knowledge about vibrations.
Peter Jönsson, Centre for Vibration Comfort (CVK) for being a totally
honest and reliable partner in discussing whole body vibration. Always their
when I best needed you! Thank you for your support.
Olle Hillborg and Erik Mårtensson Djäken, Danderyd Innovation (DSI),
helped with the risk analysis and was a great and supportive partner in our
discussions, always there and willing to help.
My loving husband Göran for love and good support in my enterprise and
for your exceptional tolerance when paper covered our kitchen table! Thanks
also to Jonas, Malin and Kalle, my very supportive children! You are the
essence of my life!
Financial support was gratefully received from The Board of Research for
Health and Caring Sciences, Handikapp & Habilitering (Habilitation
services), the National Association for Disabled Children and Youths, King
Oscar II´s and Queen Sophia´s Golden Wedding Memorial, The prototype of
the platform was built by the Royal Institute for Technology (KTH) and
Löfgren Engineering AB with grants from ALMI Stockholm AB and the
City of Stockholm Inventors award and Norrbacka-Eugenia Foundation
administered by Swedish Institute of Assistive Technology, Arts in Hospital
and Care as Culture, and the Agne Johansson Memorial Foundation.
27
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31
APPENDIX
Medical device; rules and regulations
A medical device constitutes of a large amount of products, from a simple
plaster, DEXA and X-ray machines, to technical aids for disabled persons.
The medical device will be put in different classes according to the risks for
the patients and users. Devices with the highest risk (class III) are invasive,
if the devices transmits energy to the human body they belong to class II,
and the simplest form of medical devises are class I products. The vibrating
platform transmits energy to the human body; it might have effects on bone
mass and circulation, and belongs to class IIa. The organization for control
of all medical devices and pharmaceuticals in Sweden is a national authority,
the Medical Products Agency (Läkemedelsverket). They are responsible for
regulation and surveillance of the development, manufacturing
and marketing of drugs and other medicinal products. Their task is to ensure
that both the individual patient and healthcare professionals have access to
safe and effective medicinal products and that these are used in a rational
and cost-effective manner.
Basic requirements
According to the Swedish Medical Devices Act (1993:584) and the Medical
Devices Ordinance (1993:876) a medical device shall achieve its intended
purpose as designated by the manufacturer and involve no unacceptable risk
to patients, staff or third parties.
The intended use of the vibrating platform was to promote bone mass
through self induced movement that gives a whole body dynamic loading of
the skeleton. It was also intended to be used by persons who need a Standing
shell, which means that their legs are fastened in a straight position. The
European Union produces directives to be followed to assure security. When
it comes to vibration, the EU directive 2002/44/EG is applicable.
Essential requirements
The essential requirements are an extension of the basic requirements. In
brief, the essential requirements state that safety and performance must be
documented, and that potential side effects and risks must be described. The
manufacturer must also have performed an analysis, showing that the
benefits of the device are considered to outweigh the side effects.
Information concerning use, intended purpose, risks etc shall be stated on the
device or, if this is not possible, in accompanying instructions.
The manufacturer’s internal control documentation in combination with a
technical file and a declaration of conformity asserting that the device
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complies with the requirements is needed before the product can reach the
market (LVFS 2009:18).
Third party assessment
For class II and III devices it is necessary that an assessment is carried out
by a third party, a so called Notified Body, to demonstrate that the device
complies with the requirements. A Notified Body is an independent testing
and/or certification organization which has been deemed to possess
sufficient competence and quality to evaluate the conformity of goods and
services. Swedish Notified Bodies that have been designated by SWEDAC
(Swedish Board for Accreditation and Conformity Assessment) fulfill these
requirements. It is sufficient for the manufacturer to carry out a conformity
assessment on his devices in one country in order to gain access to the entire
European market.
Standards
To put a medical device on the market in Europe, standards need to be used
during and after production and market introduction. Technical
specifications are to be found in standards. The so called harmonized
standards have been developed by the western European standardization
organizations: the European Committee for Standardization (CEN),
European Committee for Electro technical Standardization (CENELEC) and
European Telecommunications Standards Institute (ETSI) on mandates of
the EU Commission. Harmonized standards are presumed to comply with
the essential requirements in the directives. The standards are of importance
for the design, manufacturing and procurement. The intended use of the
device decides what standards to use to fulfill the requirements of
Läkemedelsverkets författnings samling, (LVFS) 2003:11 and LVFS
2009:18. The following standards apply to a medical device:
 EN ISO 14971:2007 Medical devices – Application of risk
management to medical devices (ISO 14971:2007)
 EN ISO 13485:2003 Medical devices - Quality management systems:
Requirements for regulatory purposes (ISO 13485:2003)
 EMC: EN 60601-1-2:2007
 EN 60601-1-1-2:2007 Medical electrical equipment – Part 1-2:
General requirements for basic safety and essential performance –
collateral standard: electromagnetic compatibility – Requirements and
tests.
 EN 60601-1:1990 Medical electrical equipment – Part 1: General
requirements for safety IEC 60601-1:1988.
 SS-EN 12182 Technical aids for disabled persons - General
requirements and test methods
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 SS-ISO 2631-1 Vibration and shock-Evaluation of human exposure to
whole-body vibration
 EN 980:2008 Symbols for use in the labeling of medical devices.
 EN ISO 1041:2008 Information supplied by the manufacturer of
medical devices.
A technical file according to European Medical Devices Directive
(MDD) 93/42/EEC and a quality system complying with LVFS
2009:18 are also needed. When these requirements are met, a
Conformité Européenne (CE) - mark could be placed on the product
and the product will then be qualified to be released on the European
market.
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