Physical activities of Patients with adolescent idiopathic scoliosis (AIS): preliminary longitudinal case–control study historical evaluation of possible risk factors
McMaster et al. Scoliosis
Physical activities of Patients with adolescent idiopathic scoliosis (AIS): preliminary longitudinal case-control study historical evaluation of possible risk factors
Marianne E McMaster 0
Amanda Jane Lee 1
R Geoffrey Burwell 2
0 Scottish National Paediatric, Spine Deformity Centre, Royal Hospital for Sick Children , Edinburgh EH9 1LF , UK
1 Medical Statistics Unit, University of Edinburgh , Teviot Place, Edinburgh EH8 9AG , UK
2 Centre for Spinal Studies and Surgery, Queen's Medical Centre Campus , Nottingham , UK
To our knowledge there are no publications that have evaluated physical activities in relation to the etiopathogenesis of adolescent idiopathic scoliosis (AIS) other than sports scolioses. In a preliminary longitudinal case-control study, mother and child were questioned and the children examined by one observer. The aim of the study was to examine possible risk factors for AIS. Two study groups were assessed for physical activities: 79 children diagnosed as having progressive AIS at one spinal deformity centre (66 girls, 13 boys) and a Control Group of 77 school children (66 girls, 11 boys), the selection involving six criteria. A structured history of physical activities was obtained, every child allocated to a socioeconomic group and examined for toe touching. Unlike the Patients, the Controls were not X-rayed and were examined for surface vertical spinous process asymmetry (VSPA). Statistical analyses showed progressive AIS to be positively associated with social deprivation, early introduction to indoor heated swimming pools and ability to toe touch. AIS is negatively associated with participation in dance, skating, gymnastics or karate and football or hockey classes, which might suggest preventive possibilities. There is a significantly increased independent odds of AIS in children who went to an indoor heated swimming pool within the first year of life (odds ratio 3.88, 95% CI 1.77-8.48; p = 0001). Furthermore fourteen (61%) Controls with VSPA compared with 9 (17%) Controls without VSPA had been introduced to the swimming pool within their first year of life (P < 0.001). Early exposure to indoor heated swimming pools for both AIS and VSPA, suggests that the AIS findings do not result from sample selection.
Scoliosis; Physical activities; Risk factors; Etiology; Swimming pools; Toe touching
This paper reports a preliminary longitudinal study of
the physical activities of children obtained historically
for Patients with progressive adolescent idiopathic
scoliosis (AIS) and Controls. For reasons given in Appendix I,
this text describing the research is a full account of that
previously presented [1-3].
The cause of AIS is unknown, it is generally considered
to be multifactorial in origin and thought to have separate
factors for curve initiation and progression [4-6]. There is
support for the view that genetics stipulates the course of
AIS [7-9]. Wynne-Davies , examining the etiology of
some common skeletal deformities including infantile
idiopathic scoliosis, concluded that all are likely to have a
common multifactorial genetic background associated
with differing intrauterine or postnatal environmental
factors. Monozygotic twins have been used to demonstrate
the role of environmental factors in determining complex
diseases and phenotypes, but the true nature of the
phenotypic discordance remains poorly understood
[11,12]. In the last decade, sporadic reports have suggested
environmental factors are involved in the etiopathogenesis
and phenotypic expression of AIS .
To our knowledge there are no publications that have
evaluated physical activities in relation to the
etiopathogenesis of AIS other than sports scolioses [13,14] and
trunk asymmetries with swimming . The aim of the
study was to examine possible risk factors for AIS; and
in particular to test whether one or more of a variety of
physical activities is related to the presence or absence
of progressive AIS.
Subjects and methods
Selection of subjects
One observer (MM) obtained the histories and undertook
the physical examinations. Patients and Controls were
excluded if they did not fulfil the Six Criteria for selection
and/or their family history was unknown, namely: being at
boarding school or university and were unable to attend
with their mother; from a one parent family; was adopted
or a parent had been adopted (Appendix II).
Six criteria for further selection of subjects
Patients with AIS and Controls selected for the study
were defined by Six
1. Born full term.
2. Fed well - no feeding problems during 1st year.
3. Achievement of normal milestones i.e. walking and talking.
4. No hospital referrals excluding sports injuries.
5. No back pain (before diagnosis in Patient Group).
6. No family history of scoliosis.
The Patients were diagnosed as having AIS by one spine
surgeon. Initially, 100 consecutive Patients were referred
but, due to requirements for both the structured
questioning and selection by Six Criteria 79 Patients (girls 66, boys
13) were included in the study (mean age 15.1 years).
One hundred consecutive Controls were volunteers from
three schools in north and south Scotland, and 12
Controls who had recently joined a tennis centre. After
applying the Six Selection Criteria, 77 Controls (girls
66, boys 11) were included in the study (mean age
The Patients and Controls were examined before
The Patients were referred for the primary purpose of
an Integrated Shape Imaging System (ISIS) scan (which
is an optical topographic system for measuring back
shape in 3-dimensions), although the ISIS data is not
ISIS scanning requires markers to be placed on the
spinous processes defined along the length of the spine
from the vertebra prominens to L5 and it was the basis
of this technique which was adapted to assess surface
spinal asymmetry of the Controls.
Figure 1 shows the curve types of the Patients. The
mean Cobb angle was 45 degrees (range 1078). All
curves were progressive and 62 patients subsequently
had a spinal arthrodesis.
Controls - surface vertical spinous process asymmetry
Standing in an erect position to assess spinal symmetry/
asymmetry of the Controls, the observer first identified
the vertebra prominens . The observer held her left
thumb on the vertebra prominens throughout the
examination. Then, using her right thumb to palpate each
spinous process until reaching L5 and without using skin
marks, markers or a plumb line, she looks for both
lateral spinal curvature and/or axial spinal rotation to
judge the presence or absence of surface spinal
asymmetry relative to a visual vertebra prominens - L5 line,
termed here vertical spinous process asymmetry (VSPA).
The examination was repeated several times to ensure
Finally, both thumbs were placed on the posterior
superior iliac spines, Dimples of Venus, to assess leg length
inequality and a level pelvis.
In 54 hospital staff volunteers (females 52, males 2),
none known to have scoliosis, in examinations repeated
after intervals, the Observer (MM) detected VSPA in 2
but not consistent in one of the females. The palpation
of spinous processes was more difficult than in the
children because of subcutaneous fat.
The forward bending test was not used for the
Controls (Appendix III) and they were not examined
After the examination, a structured interview was
obtained in both groups. One investigator (MM) undertook
the interviews, which followed the same rigid structure
for both groups. A history of each childs physical
activities was obtained from the mother and child, who were
questioned together for a mean time of 47 minutes. The
same rigid structure of questioning was adhered to in
both the Patient and Control Groups
The questioning was divided into pre-school regular
outdoor activities and after-school and weekend activities
Figure 1 Frequency distribution of the curve types of the AIS patients.
that were undertaken at least once a week for a minimum
of three terms (1 year). The mother was asked to recall all
physical activities that her child had participated in before
5 years of age, starting before her child could walk. Use of
toys, tricycles, and bicycles with stabilizers were all
recorded, with resounding similarity between both groups.
After 5 years of age, only after-school and weekend
activities were recorded that were undertaken at least once
a week for a minimum of three terms (1 year) under the
following headings: dancing, gymnastics, karate,
swimming, football, hockey, and rowing. Horse riding was
included but was rarely a weekly activity.
Although 12 Controls were from a tennis centre, none
had participated in tennis for the minimum of three
terms. Cycling was a regular activity undertaken in
neighbourhood by both Patients and Controls before 10
years of age. Skating (roller blade and/or ice) was also a
Winter and summer holiday activities i.e. skiing were
recorded but not analyzed, since these activities were
only undertaken for a maximum of 6 weeks.
The socioeconomic status of Patients and Controls was
established by Carstairs deprivation score  using the
Subjects postcode. This method enabled the children to
be given a score of 15 (most affluent to most deprived).
The 2 test (or Fishers exact test) was used to compare
two percentages, and odds ratios (OR) were calculated
with 95% confidence intervals (CI).
Stepwise logistic regression was used to examine
which factors were significant independent predictors of
AIS. The variables considered for entry into the model
were sex, Carstairs deprivation score (most affluent
versus the remaining four groups), whether the child
could swim by the age of 10 years, whether the child
first attended the swimming pool (on at least eight
occasions) before their first birthday, and whether the child
participated in the following activities: gymnastics or
karate, skating, horse riding, football, or hockey.
Attendance at gymnastics/karate and football/hockey
were grouped together, because participation differed
between the sexes. For this reason attendance at dance
classes was not included in the logistic regression. Two
separate models were produced, one which considered
the temporary activities of skating and horse riding, and
the other which excluded these activities from
consideration. Another separate model examined the effects of
both toe touching and introduction to the swimming
pool within the first year of life, as toe touching had not
been included in the main models as it could have been
secondary to AIS.
This study was undertaken before ethics approval was
required for such research and was prosecuted in
accordance with the Helsinki Declaration.
Table 1 shows the relationship between each possible
risk factor and group (Patient or Control).
Subjects with a score of 2, 3 or 25 combined on the
Carstairs deprivation score all had significantly
increased odds of having AIS compared with those with a
Carstairs deprivation score of 1 (most affluent), although
there was no difference for those with a Carstairs
deprivation score of 45 combined. Although when the
Table 1 Association between risk factor and asymmetry
Carstairs deprivation score
Carstairs deprivation score
Carstairs deprivation score
Asymmetry in mothers back
Hamstring muscles not tight/ability to touch toes
No previous cycling
No previous attendance at dance classes (girls only)
No previous gymnastics/karate
No previous skating
No previous horse riding
No previous playing football/hockey
Introduced to swimming pool within first year of life
Ability to swim by age 10 years
Introduced to public pool within first year (8)
Introduced to public pool within first year (12)
Introduced to public pool within first year (24)
2 test statistic or Fishers
exact test (p-value)
7.04 (2.41 20.6)
3.20 (1.16 8.83)
1.22 (0.52 2.87)
1.15 (0.59 2.24)
2.70 (1.42 5.16)
0.32 (0.03 3.11)
2.65 (1.30 5.41)
0.48 (0.04 5.41)
2.26 (1.08 4.71)
2.77 (1.40 5.49)
5.74 (2.88 11.5)
3.13 (1.50 6.53)
1.52 (0.80 2.89)
3.08 (1.60 5.94)
0.99 (0.53 1.87)
3.11 (1.61 6.02)
2.99 (1.54 5.80)
1.70 (0.84 3.44)
*All patients and controls completed every question, therefore the results are presented for 79 cases and 77 controls (with the exception of dancing classes which
only applied to girls 66 patients and 66 controls).
+Fishers exact test used rather than 2 test due to small numbers.
two most affluent groups were combined, there was no
significant increase in the odds of AIS.
was no statistically significant association for previous
regular football or hockey.
Indoor heated swimming pools
There is a significantly independent increased odds of
AIS (OR 3.08, 95% CI 1.60 to 5.94) in children who went
to an indoor heated swimming pool within the first year
of life with 58% of Patients having been introduced to an
indoor heated swimming pool within their first year
compared with 31% of Controls.
Children who did not attend dance (girls only) or
gymnastics or karate classes, or regularly participated in
horse riding and skating had higher odds of having AIS
than did those who participated in these activities. There
A significantly higher proportion of Patients than
Controls could touch their toes (80% vs 60%). Children
who could touch their toes had more than 25 times
the odds of having AIS compared with those who could
There was a statistically significant difference in the age at
which Patients and Controls regularly attended a heated
swimming pool (Fishers exact test, p = 0.0010) with
Patients introduced earlier than Controls (Table 2).
Furthermore, Controls who had VSPA had also regularly attended
an indoor heated swimming pool earlier than those
7th year or later
Can swim by age 10 years
Table 2 Age at which children were first introduced to an indoor heated swimming pool
Age regular swimming/attending pool
Controls without VSPA (Fishers exact test, p < 0.0001).
Although there was no statistically significant difference in the
percentages of Patients and Controls who could swim by
age 10 years (2 test, p = 0.99), there was a difference among
the Controls with and without VSPA (2 test, p = 0.0135).
Three of the Patients had never been to an indoor
heated swimming pool but each of the Controls had.
Independent factors associated with AIS
Using stepwise logistic regression, the following factors
were significant independent predictors of AIS:
1) Carstairs deprivation score (1 most affluent versus 25);
2) introduction to a pool within the first year of life
3) no previous skating; and
4) no attendance at gymnastics or karate classes
Children who were introduced to a pool within the
first year of life had 39 times the odds of having AIS
than did those who were not introduced to the pool.
Whereas children who had a Carstairs deprivation score
of 25, had 2.8 times the odds of having AIS compared
with those in the most affluent category (score of 1).
Children who had no previous skating and no previous
gymnastics or karate were 5.1 and 2.8 times the odds
respectively of having AIS compared with those who
participated in these activities.
A further model (Table 4) was derived with stepwise
logistic regression that excluded skating and horse
riding, since these activities were regarded as temporary.
The model was similar to that which included all
activities except that no previous skating was replaced with
no previous football or hockey. The odds of having AIS
among those with a Carstairs deprivation score 25 and
no previous gymnastics or karate increased slightly (to
3.3 and 3.5 respectively), and there was 2.1 times the
odds of AIS among those who did not undertake football
or hockey compared with those who did participate in
Early introduction to swimming pool and toe touching
Of the 45 Patients who had been taken to a public
swimming pool in their first year of life, 39 (87%) could touch
their toes at time of examination.
Whereas 23 Controls who were taken to a public
swimming pool before 1 year of age, 14 (61%) could
touch their toes.
Using both early introduction to swimming and toe
touching together in a logistic regression model, both
were significant independent predictors of AIS. There
was 2.86 (95% CI 1.46 to 5.60) times the odds of AIS for
those introduced to the pool (8 occasions) within their
first year compared with those who were not introduced
Table 3 Significant independent predictors of asymmetry (temporary activities included but touching toes excluded)
using Carstairs 1 versus 25 and eight swimming visits
No previous skating
Introduced to swimming pool within first year (8)
Carstairs Deprivation score (25 = most deprived)
No previous gymnastics/karate
Table 4 Significant independent predictors of asymmetry (temporary activities and touching toes excluded) using
Carstairs 1 versus 25 and eight swimming visits
Introduced to swimming pool within first year (8)
No previous gymnastics/karate
Carstairs Deprivation score (25 = most deprived)
No previous football/hockey
to the pool (p = 0.002); and there was 2.35 (95% CI 1.13
to 4.91) times the odds of AIS for those who could
touch their toes compared with those who could not
(p = 0.023).
AIS and control samples
The samples are not large but were considered adequate
for the statistical tests applied in a preliminary study but
with the size of our samples, we cannot exclude the
possibility of random variation contributing to the findings
(Appendix II). The mean ages of the samples are not
significantly different; the greater variance of the AIS group
did not affect the collection of historical evidence. The
selection of 12 Controls from a tennis centre might have
affected the findings, since they could have been more
active, though none of these children had played tennis
every week for a period of three terms.
The structured history taking of physical activities
helped with the problem of obtaining reliable memories
over several years. The history was always procured from
the mother often accompanied by the father. The
observer (MM) was impressed by the capacity of the mothers
to recall the early years of their childs physical activities;
less so for later years where the child was noted to have
a clear recollection.
Independent factors associated with AIS
Five significant independent predictors for AIS were:
1) increased deprivation;
2) introduction to a swimming pool within the first
year of life (eight occasions)
3) no previous skating (model including temporary
4) no attendance at gymnastics, or karate classes; and
5) no attendance at football or hockey classes (model
excluding temporary activities).
These are predictive in the statistical models and only
possible risk factors for AIS while awaiting the results of
Association of AIS in more deprived socioeconomic groups
Significantly increased odds of AIS was found in more
deprived socioeconomic groups (score 25) than in the
most affluent group, score 1. The findings are
inconsistent with those reported by Ryan et al.  who reported
that AIS was more common in high than in low
socioeconomic groups. Carstairs deprivation score is not a
precise indicator of socioeconomic group as it is defined
at a geographical area level (postcode) rather than at an
individual level. This could be one reason for the
However, since an association between Carstairs
deprivation score and participation in various activities
was noted, it was necessary to include Carstairs
deprivation into the model (as it was a confounder) so
that assessment of which factors are significant
independent predictors of AIS can be considered, i.e.
factors that have an association with AIS after taking
deprivation into account.
Association of AIS with introduction to a swimming pool
within the first year of life
The association of AIS with early exposure to indoor
heated swimming pool, if not due to sampling and
chance, does not prove a causative link between AIS and
such exposure, but only the unproven possibility of such
a link for which an hypothesis has been formulated .
Two asymmetries of the spinal column
Two asymmetries of the spinal column were identified
namely, in (a) the Patients with AIS with spinal
radiographs and (b) the Controls with VSPA.
The finding of VSPA associated with early exposure to
indoor heated swimming pools was unexpected and an
original finding. This VSPA method is not generally used
by spine surgeons in such detail to assess lateral spinal
curvatures of the spine. The observer (MM) used this
method as a result of 17 years experience with ISIS
scanning where the physical identification of spinous
processes is needed in the preparation for ISIS scanning.
What does the presence of VSPA indicate?
VSPA was found to be common in the Controls (30%).
As the Controls were not referred for X-ray examination
due to ethical restriction, their Cobb angles of the
VSPAs are not known. Besides mild structural lateral
spinal curvatures VSPAs may express pelvic tilt scoliosis
and postural scoliosis. The Controls were not examined
neurologically. In the year after they were examined,
seven of the Controls with VSPA were referred to the
scoliosis clinic by their general practitioners.
Not the result of sample selection?
The association of attendance as infants to indoor
heated swimming pools with each of AIS and VSPA,
suggests that this association for AIS children did not
result from sample selection.
Separate initiating and progressive factors for AIS?
In the Control group, strong evidence of an association
between VSPA and early indoor pool attendances, is the
finding that 61% of those with VSPA had been taken to
an indoor heated swimming pool as infants. The evidence
is consistent with the speculation that VSPA relative to
AIS may express either:
(a) an initiating factor(s) in swimming pool ambience
for AIS with other factors needed for curve
(b)a weaker initiation.
Environmental factor(s) for AIS and VSPA?
The indoor heated swimming pool association with the
later expression of AIS and VSPA raises the
speculation that there might be other environmental factors
acting in the first year of life to initiate the later
expression of AIS that differ around the world, with
an environmental effect suggested from research in
Scotland (see below ethnicity, latitude and swimming
Number of swimming pool visits and AIS
There were increased odds of AIS for children who were
introduced to the swimming pool within the first year of
life if attendance was defined as eight or more or 12 or
more visits, but not if attendance was defined as 24 or
more visits. It is not clear why this might be the case,
and this needs to be examined in more detail in further
a) the sampling of more active Controls, and/or
b) the relatively reduced exposure to these physical
activities predisposed the children to progressive
c) children with AIS feel less confident with physical
activities and do not participate as much as other
Point (b) raises the possibility that increased physical
activities as possible therapy, may protect against AIS by
involving neuromuscular feedback mechanisms common
to all joints .
Herman and co-workers  suggested that idiopathic
scoliosis involves visuo-spatial perception impairment. If
so, perhaps the introduction of specific physical activities
to more members of a community by facilitating the
onset of balance skills within the framework of posture
might prevent some children from getting progressive
Association of toe touching with AIS
After correction for deprivation score, a significant
association between AIS and toe touching (positive risk
factor) was recorded compared with early swimming
(positive risk factor), and not doing various sporting
activities, which potentially has therapeutic implications.
Toe touching involves separate contributions from the
hip, lumbar, and thoracic spines in the sagittal plane
. Joint laxity is associated with AIS  and although
the hypothesis that a defect of connective tissues is a
causative factor, it is not established.
The increased ability to toe touch in Patients with AIS
could be associated with the physique of the children or
with factors such as joint laxity that are associated with
the cause of the spinal deformity . Taylor and
Melrose  support the hypothesis that collagen
abnormalities in the intervertebral disc have a contributory
role to the development and evolution of the curvature.
Ethnicity, latitude and swimming pools
Smyrnis and colleagues  noted an increased prevalence
of spinal asymmetry in children with fair hair and blue eyes
in their study of about 3500 Greek schoolchildren.
Grivas and colleagues  have shown the prevalence of
AIS according to geographical location in the northern
hemisphere, with the incidence decreasing as the latitude
approaches the equator. The investigators suggest that these
data might represent real environmental, geographical,
genetic, or racial factors for this disease. Environmentally, it
seems reasonable to link the geographical latitude of AIS to
the location of indoor heated swimming pools - and Scotland
has a northern climate. The heating of a pool and its enclosure
is determined by the prevailing outdoor temperature.
Children, swimming pools, disease, conditions and
How swimming in an indoor heated swimming pool early
in the first year of life may be associated later in life with
the development of AIS and VSPA is unknown. It may be
due to sampling differences, or be related to causation.
Sampling seems less likely by the finding that the early
swimming pool exposure relates to both AIS and the
VSPA of healthy children. More research is needed.
Other research has shown detrimental exposure to
chemicals that are found in swimming pools. No data on
chemicals in the pool ambience during the period of this
study are known to us.
Bessac and colleagues  found that that chlorine
triggers nerve endings not only in the lungs but also in
peripheral tissues of mice. Nystad and co-workers 
have noted that taking a baby swimming increases
infections of the respiratory tract and middle ear. In a study
assessing children exposed to the air of
indoorchlorinated pools, Bernard and colleagues  reported
a link to asthma and chronic airway inflammation, which
they suggest could be due to an irritant gas
trichloramine (nitrogen trichloride) contaminating the air of
indoor-chlorinated pools. Chlorine reacts with bodily
proteins to form chloramines, the most volatile and
prevalent of which in the air above swimming pools is
nitrogen trichloride . Waterborne pathogens are
destroyed by chlorine; however, when sweat, urine, and
faecal bacterial levels overpower the chlorine
hypochloride, a breakdown product such as trihalomethane is
formed . No child with asthma and receiving
prescribed medication for their disease would have been
included in our studies as either a Patient or a Control.
Grandjean and Landrigan  reported that one in six
children has some type of developmental disability,
usually involving the nervous system, and that developing
brains are much more susceptible to toxic chemicals
than those of adults. Furthermore, they believed that
identifying the effects of industrial chemical pollution is
difficult because patients might not produce symptoms
for several years or even decades. The article concluded
The combined evidence suggests that
neurodevelopmental disorders caused by industrial chemicals has
created a silent pandemic in modern society.
Barker and colleagues  showed that the origins of
important chronic diseases in adult life might lie not
only in the intrauterine environment but also in early
postnatal life. Whether or not this concept is applicable
to the findings reported here is unknown.
1. Statistically significant associations were found
between AIS and each of social deprivation, early
introduction to an indoor heated swimming pools,
not participating in some sporting activities and
ability to toe touch. These are possibly positive and
negative risk factors for AIS, which may have
2. The association of AIS with early exposure to indoor
heated swimming pool, if not due to sampling and
chance, does not prove a causative link between AIS
and such exposure, but only the unproven possibility
of such a link for which an hypothesis has been
3. Early exposure to indoor heated swimming pools was also associated with vertical spinous process asymmetry (VSPA).
4. VSPAs may express mild structural lateral
curvatures, pelvic tilt scoliosis and postural scoliosis.
5. The association of attendance as infants to indoor heated swimming pools with each of AIS and VSPA, suggest that this association for AIS children may not result from sample selection.
6. The evidence is consistent with the speculation that
VSPA relative to AIS may be an expression of either:
(a) an initiating factor(s) in swimming pool
ambience for AIS with other factors needed for
curve progression; or (b) a weaker initiation.
7. The speculation suggested that there might be other environmental factors acting in the first year of life to initiate the later expression of AIS, that differ around the world
8. Confirmation of these preliminary findings is needed.
This paper provides a full account of that published
privately in abridged form with one Table by the
International Research Society of Spinal Deformities meeting
at the University of British Columbia, Canada in 2004 .
The research led to a further publication by the writer .
The Patient Group consisted of 79 adolescents. Of which
66 (84%) were girls (mean age 151 years, SD 3 0, range
10 years 9 months25 years 3 months) and 13 (16%)
were boys (mean age 14 years 10 months, SD 1 8, range
11 years 2 months18 years 7 months at time of
ISIS (Integrated Shape Imaging System) is an optical
topographic system for measuring back shape in
3dimensions. The lateral spinal curvature measured by
ISIS equates with the radiological Cobb angle. ISIS is
very unlikely to reliably detect scolioses below 10
degrees (Shannon T, personal communication). Cobb
angles below 10 degrees is viewed as normal.
77 consecutive Controls: all of whom met the six
inclusion criteria. 66 (86%) were girls (mean age 14 years
6 months, SD 11, range 11 years 9 months16 years
11 months) and 11 (14%) boys (mean age 15 years
2 months, SD 19, range 12 years 6 months18 years at
the time of interview).
Age of patients and controls
There was a significant difference in the variance in the
ages among the Patients (SD 2.86 years) compared with
Controls (SD 1.22 years) as Patients ranged from 10.8 to
25.3 years and Controls ranged from 11.8 to 18.0 years.
Using a t-test with unequal variance, there was no
statistically significant difference in the mean age 1.13,
df = 106, p = 0.26) of Patients (mean age 15.1 years) and
Controls (mean age 14.7 years).
The study is sufficiently powered statistically to examine
the primary aim of examining early exposure to
swimming in relation to AIS. With an anticipated exposure to
early swimming among the Controls of 30% and with an
increased risk of 3 or more, testing at the 5% significance
level with 80% power, one would require 55 Patients and
55 Controls. With 90% power, one would require 73
Patients and 73 Controls. The study had 79 Patients and
77 Controls so we had more than 90% power which is
the maximum generally used in sample size calculations.
The children in both the Patient and Control Groups
were Caucasian, apart from one female patient. This
patient was non-white judged by the third generation, but
because of the weakness of this factor was not excluded
from the study.
Six children were considered overweight as defined by a
fat fold below the rib cage (two Patients, four Controls).
Their physique was not deemed to inhibit toe touching
or the observers ability to palpate the spinous processes.
Forward bending test (FBT)
The FBT, quantified with the Scoliometer  has never
been used in the Edinburgh Spinal Deformity Centre.
This is because:  the FBT provides a visual and/or
digital estimate of axial trunk rotation and only
indirectly of lateral spinal curvature, and  long experience
in applying markers to each spinous processs from
vertebra prominens to L5 preparatory to ISIS scanning,
led to the observer (MM) to apply this technique to the
The authors declare that they have no competing interests.
MM planned the study and collected the data. AL undertook the statistical
analyses. GB contributed to the interpretations. All authors contributed to
writing the text, read and approved the final version.
1. McMaster M , Lee AJ , Burwell RG . Physical Activities of Patients with Adolescent Idiopathic Scoliosis (AIS) Compared with a Control Group . Implications for Etiology and Possible Prevention . In: Sawatzky BJ, editor. International Research Society of Spinal Deformities Symposium , 2004 . Vancouver: University of British Columbia; 2004 . p. 68 - 71 .
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