Low Body Mass Index for Early Screening of Adolescent Idiopathic Scoliosis: A Comparison Based on Standardized Body Mass Index Classifications

Journal Pre-proof Low body mass index for early screening of adolescent idiopathic scoliosis: A comparison based on standardized body mass index classifications Suhee Kim, PhD, RN, Assistant Professor, Ju-Yeon Uhm, PhD, RN, Assistant Professor, Duckhee Chae, PhD, RN, Assistant Professor, Yunhee Park, PhD, RN, Assistant Professor PII:

S1976-1317(19)30543-2

DOI:

https://doi.org/10.1016/j.anr.2019.12.003

Reference:

ANR 349

To appear in:

Asian Nursing Research

Received Date: 15 July 2019 Revised Date:

25 December 2019

Accepted Date: 26 December 2019

Please cite this article as: Kim S., Uhm J.-Y., Chae D. & Park Y., Low body mass index for early screening of adolescent idiopathic scoliosis: A comparison based on standardized body mass index classifications, Asian Nursing Research, https://doi.org/10.1016/j.anr.2019.12.003. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Korean Society of Nursing Science. Published by Elsevier B.V.

Low body mass index for early screening of adolescent idiopathic scoliosis: A comparison based on standardized body mass index classifications

Suhee Kim, PhD, RN Assistant Professor, School of Nursing and Research Institute of Nursing Science, Hallym University, Hallimdaehak-gil, Chuncheon-si, Gangwon-do, 24252, South Korea. E-mail: [email protected], Tel: 82-33-248-2718

Ju-Yeon Uhm, PhD, RN Assistant Professor, Department of Nursing, Pukyong National University, Yongso-ro 45, Nam-Gu, Busan, 48513, South Korea E-mail: [email protected], Tel: 82-51-629-5790, Fax: 82-51-629-5789

Duckhee Chae, PhD, RN Associate Professor, College of Nursing, Chonnam National University 160 Baekseo-ro, Dong-gu, Gwangju, 61469, South Korea E-mail: [email protected], Tel: 82-62-530-4942, Fax: 82-62-530-4544

Yunhee Park, PhD, RN Assistant Professor, Department of Nursing, College of Medicine, Wonkwang University 460, Iksandae-ro, Iksan, Jeonbuk, 54538, South Korea E-mail: [email protected], Tel: 82-63-850-6028, Fax: 82-63-850-6060

Corresponding author: Ju Yeon-Uhm Assistant Professor, Department of Nursing, Pukyong National University, Yongso-ro 45, Nam-Gu, Busan, 48513, South Korea E-mail: [email protected], Tel: 82-51-629-5790, Fax: 82-51-629-5789

Acknowledgements The abstract has been selected for a poster presentation at the 23nd East Asian Forum for Nursing Scholars (EAFONS) 2020.

Funding This study is supported by Korea National Research Fund (NRF-2017R1D1A1B03032183) and Hallym University Research Fund (HRF-201709-002).

Conflict of interest statement The authors declare that they have no competing interests.

Running head: Low body mass index and adolescent idiopathic scoliosis

1

Low body mass index for early screening of adolescent idiopathic scoliosis: A comparison

2

based on standardized body mass index classifications

3

Running title: Low BMI and AIS

4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 1

24

Abstract

25

Purpose: Scoliosis is a common musculoskeletal problem in adolescents. This study aimed to

26

identify the prevalence of adolescent idiopathic scoliosis (AIS) and its associated factors among

27

Korean adolescents. The prevalence of thin individuals among students with AIS was compared

28

based on body mass index (BMI) classifications.

29

Methods: This study was a secondary data analysis and used the 2016 Korean National Health

30

Examination for School Students data. Data from 16,412 students were analyzed using

31

descriptive statistics, chi-square tests, and logistic regression analysis.

32

Results: The prevalence of AIS was higher in female students (3.8%) than in male students

33

(1.6%), and a higher school year was a risk factor for AIS in both sexes. In female adolescents,

34

scoliosis was associated with thinness; however, the risk of AIS was inversely associated with

35

overweight/obesity in both sexes. The prevalence of thin female students with scoliosis differed

36

based on the criteria used: 3.3% by the World Health Organization criteria and 14.3% by the

37

International Obesity Task Force criteria.

38

Conclusions: The prevalence of thin students with scoliosis could increase by up to four times

39

depending on the BMI criteria. For early screening of thin people at risk of AIS among female

40

students, the criterion of IOTF should be used as it is more permissive of thinness. This is also

41

due to the underestimation of AIS prevalence when using the BMI Z score of the WHO cut-off.

42 43 44 45

Key Words: adolescents, body mass index, scoliosis, thinness

46 2

47

Introduction

48

Scoliosis is a growth-related disorder occurring during periods of rapid growth of the

49

musculoskeletal system before skeletal maturity. It is one of the most common musculoskeletal

50

problems in adolescents. The prevalence of childhood scoliosis has been reported to range

51

broadly from 0.5% to 5.2% depending on the country, and its prevalence in Turkey, Germany,

52

and Korea have been reported to be 0.47%, 5.2%, and 3.3%, respectively [1]. One study, using

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national data, reported that the incidence of surgery for scoliosis is increasing [2]. Adolescent

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idiopathic scoliosis (AIS) affects patients aged ≥10 years and comprises 85% of cases in the

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USA and 55% of cases in Great Britain [3]. Although AIS can be asymptomatic, back pain is

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present in approximately 32% of AIS cases [3]. In patients with a large thoracic curve, untreated

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AIS can cause pulmonary symptoms such as decreased pulmonary function and shortness of

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breath [4]. The US Preventive Services Task Force reported that surgery is recommended in AIS

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with a Cobb angle of 40° to 50°, and screening tests can detect AIS [5]. The sensitivity on using

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the forward bend test or topography for screening test in a school-based program was 84.4% to

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100% [5]. The pooled positive predictive value for detecting curves ≥10° was 28.0% [6]. The

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rate of confirmation by radiographs was 94.2% following the referral of children defected via the

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forward bend test by a trained personnel in a school-based screening program [7]. Early

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detection through screening tests to prevent the occurrence of severe scoliosis with retardation of

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curve progression before skeletal maturity is one of important health issues in school-aged

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population.

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The etiopathogenesis of AIS remains unknown. Several etiologies have been postulated as

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follows: genetic or hereditary factors, neurological disorders, hormonal and metabolic

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dysfunction, skeletal growth, biomechanical factors, and environmental factors [3, 8]. It is well 3

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established that genetic factors play a role in AIS development [9, 10]. AIS is 2-10 times more

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common in women than in men and typically progresses during pubertal growth [11]. The

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prevalence of scoliosis increases with increasing age [12], particularly in adolescents aged 13–17

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years [1]. Puberty is thought to be initiated by genetic and lifestyle factors, leading to the

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development of AIS [13]. Additionally, melatonin deficiency and joint hypermobility during

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exercise have been shown to be related to increased prevalence of scoliosis [14].

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Moreover, low body mass index (BMI) has been reported to have greater effects on the

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prevalence [15] and severity of AIS [16]. The Cobb angle in the AIS population was shown to be

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negatively correlated with body weight [17]. One of the mechanisms underlying the association

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between low BMI and scoliosis is altered leptin bioavailability [15, 18]. As BMI can be

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evaluated through school screening, early detection of and intervention for scoliosis could delay

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disease progression among those in the low BMI group. Selection of populations with an

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increased risk of AIS should take precedence using clearer definitions of BMI to implement

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these interventions in the low BMI group. However, the criteria for low BMI vary. The criteria

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for thinness in children and adolescents are commonly based on three classification methods:

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<18.5 kg/m2 by the International Obesity Task Force (IOTF) [19], <-2 standard deviations (SD)

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by the World Health Organization (WHO) [20], and <5th percentile based on the BMI-for-age

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growth used by the US Centers for Disease Control (CDC) [21]. In Korea, <5th percentile based

88

on the BMI-for-age growth was followed in the Korean Centers for Disease Control (KCDC)

89

criterion [22], which was developed based on the US CDC method using Korean child-

90

adolescent data.

91

Like these, the use of different criteria for low BMI could cause confusion in the selection of

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high-risk population for the implementation of the screening program. The accuracy of the 4

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screening test is increased (the sensitivity and specificity are higher and false-positive and false-

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negative rates are lower) when a scoliometer and topography are used together rather than when

95

a scoliometer alone with the forward bend test [5]. However, multiple screening tests during

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school screening for all students are expensive. Therefore, it may be cost-effective to selectively

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detect high-risk subjects, such as underweight individuals, and perform additional tests in only

98

these subjects. Cut-off levels for low BMI related to scoliosis development should be designated

99

to screen for AIS. However, information regarding the prevalence of AIS based on BMI criteria

100

in the literature is limited. Therefore, the primary aim of this study was to identify the prevalence

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of scoliosis among Korean adolescents, and the secondary aim was to determine factors

102

associated with scoliosis in Korean adolescents. In addition, we compared the differences in the

103

prevalence of thinness among adolescents with scoliosis according to three BMI criteria and

104

identified the most appropriate BMI criterion for taking preventive measures for scoliosis in

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adolescents.

106 107

Methods

108

Study design and participants

109

This was a secondary data analysis study on data from the 2016 Health Examination for

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School Students (HESS), a national health examination conducted annually by the Korean

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Ministry of Education based on the School Health Act [23]. The sample schools were selected to

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identify student health status and analyze health problems, and the schools were stratified by

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region, city size, and type of school (elementary, middle, and high schools). Next, the sample

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schools were selected based on the probability proportional to size sampling in each stratum, and 5

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one class was randomly selected per grade level. Although HESS is conducted throughout the

116

country, only the data from a selection of schools without personal information are provided for

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research studies. As the data were publicly available, this study was exempted from Institutional

118

Review Board review.

119

The HESS is categorized into three domains: (1) anthropometric measurement, (2) physical

120

examination (review of system), and (3) health surveys (regarding sleep, exercise, and diet).

121

Growth measurements and health surveys are conducted annually, whereas physical examination

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is conducted in the first (7-year-olds), fourth (10-year-olds), seventh (13-year-olds), and 10th

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grades (16-year-olds). Chest radiography is used to screen for tuberculosis and scoliosis only in

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the seventh and 10th grades. For students who needed a physical examination, growth

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measurements and health surveys were performed at the hospital. For other students, growth

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measurements and health surveys were performed by the school nurse at each school.

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The 2016 HESS included 82,883 students from grade 1 to grade 12 among 765 schools.

128

Among them, only 16,613 students (seventh and 10th grades) were eligible for health screening

129

and chest X-ray imaging. The final analysis included 16,412 students, excluding 29 with missing

130

data of the scoliosis examination and 172 who were diagnosed with diseases such as muscular

131

skeletal disease, cardiovascular disease, and respiratory disease.

132

Measures

133

1) Scoliosis: Scoliosis was diagnosed based on the results of a physical examination or chest

134

X-ray examination. In the physical examination, the Adams Forward Bend Test was used to

135

diagnose scoliosis. Lateral flexion is apparent if one side is higher than the other. Lateral

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vertebral flexion of >10° is diagnosed as scoliosis. On chest X-ray examination, scoliosis was 6

137

confirmed using the Cobb method, the standard technique for the measurement of spinal

138

curvature and deformities. Curves of >10° were diagnosed as scoliosis [23].

139

2) Individual characteristics: Of the variables reported to be associated with AIS in previous

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studies, the following individual characteristics that were available from the original data were

141

used: demographic characteristics (sex and grade), health status (BMI), and health behaviors

142

(exercise and duration of sleep).

143

3) BMI criteria

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·IOTF [19, 24]: The IOTF provides age- and sex-specific cut-off points regarding overweight

145

and obesity in 2–18-year-olds based on the percentiles at age 18 years as 25 and 30 kg/m2,

146

considering the WHO classification of adult overweight and obesity criteria, respectively. In

147

addition, the IOTF cut-off values provided three grades of thinness based on percentiles at age 18

148

years as a BMI of 18.5, 17, and 16 kg/m2, based on the WHO’s mild, moderate, and severe

149

classifications of adult thinness criteria, respectively. This study used the grade 1 cut-off value

150

for thinness (mild, BMI <18.5 kg/m2).

151

·WHO [20]: The WHO growth reference is based on BMI-for-age z-scores in children and

152

adolescents (aged 5–19 years). The WHO cut-off values defined overweight, obesity, and two

153

grades of thinness as follows: overweight if BMI >+1SD, obesity if BMI >+2SD, thinness if

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BMI <-2SD, and severe thinness if BMI <-3SD. This study used the thinness reference (BMI of

155

<-2SD).

156

· KCDC [22]: Obesity was defined as a BMI of ≥95th percentile, and overweight was defined as

157

a BMI of ≥85th percentile and <95th percentile. Normal weight was defined as a BMI of ≥5th

158

percentile and <85th percentile, and wasting was defined as a BMI of <5th percentile, based on

159

BMI-for-age growth charts (girls/boys aged 2–18 years). This study used the wasting cut-off 7

160

(BMI of <5th percentile) from the 2017 Korean National Growth Charts.

161

Data analysis

162

We used descriptive statistics to identify the prevalence of scoliosis and individual

163

characteristics using the IOTF criterion. The IOTF criterion, as an international criterion, can

164

facilitate the comparison of our results with those reported in other countries with regard to the

165

relationship between BMI and scoliosis. For bivariate analysis, the chi-square test was performed

166

to assess the associations between individual factors and scoliosis in adolescents. Further, factors

167

affecting scoliosis were analyzed using multiple logistic regression by sex, which included

168

variables identified as significant in bivariate analysis. The reason for dividing the sexes is that

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the prevalence of scoliosis differs between men and women and is more than two times higher in

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women. Finally, multiple logistic regressions by BMI criteria (IOTF, WHO, KCDC) were

171

performed to compare differences among BMI criteria. For all analyses, the authors used p-

172

values for two-tailed tests and considered p-values less than .05 significant. All analyses were

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performed using SPSS 23.0 (IBM Corp., Armonk, NY, USA).

174 175

Results

176

Among the 16,412 students included in the study, the total prevalence of scoliosis was 2.6%

177

(male=1.6%, female=3.8%). The prevalence of AIS was higher in female than in male students

178

(p<.001) and in those with a lower BMI (p<.001). AIS showed differences in grade (p<.001),

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exercise (p=.021), and duration of sleep (p=.020) (Table 1). In the logistic regression analysis,

180

results according to sex, the common significant predictors of AIS in male and female students

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were 10th grade and overweight/obesity. Thinness was a significant factor in female students

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only (p<.001) (Table 2). 8

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The prevalence of thin students with AIS differed according to the BMI criteria (Figure 1). In

184

male individuals, the prevalence of thinness among adolescents with AIS was 9.0%, 3.8%, and

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10.5%, according to the IOTF, WHO, and KCDC, respectively. In female individuals, the

186

prevalence of thinness among adolescents with AIS was 14.3%, 3.3%, and 12.0%, according to

187

the IOTF, WHO, and KCDC, respectively. In the logistic regression analysis results according to

188

BMI criteria, the odds ratios (OR) of thin students with AIS differed; however, all criteria were

189

significant among female students (Table 3).

190 191

Discussion

192

The prevalence of AIS was found to be 2.6% among 7th and 10th-grade students (aged 13 or

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16 years) in Korea, which is within the known range of prevalence (2%–3%) in children aged

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<16 years [3]. This was lower than the reported 3.26% prevalence in Korean children aged 10-12

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years and 13-14 years [25], but higher than the 0.97%-1.14% prevalence of children aged 11-14

196

years in China [12]. When consecutive physical examinations were performed, positive

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agreement among examiners varied from 7% to 30% [26]. In other words, the physical

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examination result alone cannot adequately confirm scoliosis. In this study, 72% of the students

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with scoliosis were diagnosed using X-ray imaging and 27.9% (121/434) by physical

200

examination alone. Therefore, the 2.6% prevalence found in this study could be an overestimate.

201

Several factors were found to be associated with the risk of AIS. The first factor was a low

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BMI. In participants who had a BMI of <18.5 kg/m2, the prevalence of AIS showed a correlation

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with BMI; the OR increased up to 1.908 in female students. Tam et al. reported that lower body

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mass showed a causal association between low BMI and AIS occurrence [15]. Similar results

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were observed in another study, in which the mean BMI was 18.6 kg/m2 in AIS and 19.8 kg/m2 9

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in controls among adolescents [27]. Therefore, school nurses and healthcare professionals should

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pay close attention to thin female adolescents to ensure early management of AIS. This can be

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explained by leptin deficiency in low BMI individuals, resulting in an increased occurrence of

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scoliosis [28, 29]. Serum leptin level was found to correlate with BMI [30]. In a population with

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AIS, body composition measurements such as BMI, fat-free mass, and fat mass index were lower

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than those in the general population [31]. Although the precise molecular mechanism remains to

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be elucidated, Burwell et al. [32] hypothesized that lower leptin levels are related to the initiation

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of asynchronous neuro-osseous growth, leading to tension in the neuraxis and tethered anterior

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vertebral growth. In contrast, low BMI was not associated with scoliosis in male adolescents.

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However, in a previous study, the BMIs of AIS participants aged 15–17 years were significantly

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lower than those of the healthy group [17]. Boys reach puberty approximately 2 years after girls

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at age 13–14 years [33]; therefore, the different outcome observed in this study is thought to be

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because our population included seventh-grade students corresponding to 13-year-old students,

219

i.e., before puberty.

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In this study, the higher BMI group was shown to have low occurrence of AIS in both sexes.

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Hershkovich et al. reported that in 17-year-old adolescents, high BMI was associated with

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decreased spinal deformities in male and female patients [34]. In addition, bone mineral density

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was reported to be significantly higher in women with obesity. On the contrary, results revealed

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that overweight and obesity can increase the thoracic curve in scoliosis. Overweight and obesity

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patients with AIS presented with a larger thoracic curve compared to normal-weight patients [35,

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36]. However, even if the spine is bent more severely with obesity, scoliosis may be difficult to

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detect. For example, the spinal curvature can easily be detected in thin students when bent;

228

however, the spinal curvature in obese students can be concealed by fat. Therefore, school nurses 10

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and healthcare professionals should pay close attention to adolescents with obesity to avoid

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missing the curved spine, and chest X-ray imaging as well as physical examination should be

231

performed for more accurate screening.

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The second factor was sex. In this study, the male-to-female ratio of students with scoliosis

233

was 1:2.3; therefore, AIS was found to occur predominantly in female adolescents [1, 11].

234

Although the difference in the prevalence of male and female adolescents with AIS according to

235

the degree of curvature is unclear, this study shows that the overall prevalence in female

236

adolescents is higher than that in male adolescents. We can speculate that hormones such as

237

estrogen and estradiol affect the development of scoliosis in female adolescents [37, 38].

238

The third factor was school year. Between both sexes, 10th-grade students (16-year-olds) had

239

a higher risk of scoliosis than seventh-grade students (13-year-olds). The prevalence of AIS

240

increased significantly with age in previous studies: 1.37~1.67% in 11~12-year-old girls, 2.22%

241

in 13~14-year-old girls, and 3.12% 16~17-year-old girls and 0.21~0.44% in 11~13-year-old boys

242

and 0.66% in 13~14-year-old boys [1]. The prevalence of scoliosis in the 15–20-year group was

243

1.14%, which was higher than 0.97% observed in the 11–14-year group [12]. The rate of AIS

244

curve progression is 1° to 2° per month during the pubertal growth spurt [3].

245

We investigated the relationship between sleep, exercise, and scoliosis, but no relationships

246

were found. Melatonin is secreted at night, and light exposure inhibits secretion of melatonin

247

[39]. A previous study investigated melatonin deficiency and scoliosis in animals [40]. In a

248

human study, those with melatonin deficiency of ≥25% showed increased prevalence of scoliosis,

249

compared with a control group [41]. However, a review article reported that there is no perfect

250

study of the etiopathogenesis of AIS with advanced understanding of the mechanisms of

251

melatonin in the development of AIS in humans [42]. In addition, the prevalence of scoliosis was 11

252

higher in adolescents who participated in various sport activities [14]. However, most studies

253

were retrospective case-control studies; hence, further studies are needed to suggest that

254

flexibility or hypermobility in some sports leads to AIS.

255

We analyzed and compared the prevalence and OR of AIS according to the thinness criteria

256

using the standardized classifications of IOTF, WHO, and KCDC. The prevalence of thinness in

257

the AIS population differed depending on the BMI criteria, ranging from 3.3% with the WHO

258

criterion to 14.3% with the IOTF criterion in female students. The OR of AIS was also found to

259

have a wide range, from 1.91 with the IOTF criterion to 2.44 in the KCDC criterion.

260

The CDC cut-off using BMI <5th percentile [27, 34] and the IOTF cut-off using BMI <18.5

261

kg/m2 [18, 31] were mainly used for the definition of underweight in previous studies on the

262

association between AIS and underweight. However, a systematic review reported that several

263

studies defined underweight using various cut-off values, such as BMI ≤20.0 kg/m2, <18.0 kg/m2,

264

<17.5 kg/m2, <3rd percentile, <4th percentile, or <20th percentile, which has highlighted a

265

limitation of these studies as they lack standardized definitions of low BMI [43].

266

In this study, the prevalence of female adolescents with low BMI (<18.5 kg/m2) using the

267

IOTF criterion was 14.3% in the AIS group, which was >27% lower than that observed using the

268

IOTF criterion in a systematic review [43]. In the literature using the CDC definition, the

269

prevalence of

270

to 6.8% [17, 44], which is comparable to the prevalence of 3.3% with the KCDC definition in

271

our study. These findings reveal that the prevalence of thinness with AIS according to various

272

definitions in this study was relatively lower than that in other studies; however, the prevalence

273

of thinness with AIS according to the IOTF definition was as high as that in previous studies.

274

Moreover, there was a great difference in the prevalence according to the definitions of low BMI;

underweight with <5th percentile among AIS group was found to range from 1.9%

12

275

the prevalence was more than two (9.0% versus 3.8% in male) to four times (14.3% versus 3.3%

276

in female) higher when using the IOTF cut-off than that while using the WHO cut-off by sex in

277

this study. In other words, this result suggests that the thinness cut-off value based on the WHO

278

definition is too strict to screen populations highly at risk of AIS. Two studies only used the

279

WHO definition (BMI Z score) [45, 46], and no study has compared the prevalence of AIS based

280

on the three standardized definitions of low BMI. In a previous study, when the WHO BMI

281

(kg/m2) percentile charts were used, a significant difference was found between the severe AIS

282

group (Cobb’s angle >40°) and moderate AIS group (Cobb’s angle 10°~39°), but the use of the

283

BMI Z score (SD) of the WHO did not present any differences between the two groups [47]. This

284

finding is speculated to be due to the underestimation of AIS prevalence by the use of BMI Z

285

score of the WHO cut-off. Unfortunately, we cannot compare the prevalence of AIS using KCDC

286

criteria with others because KCDC has not been used in the existing studies regarding prevalence

287

of AIS among Koreans. The prevalence of thinness among middle school students was 5.8%

288

using IOTF, 5.5% using KCDC, and 1.6% using WHO and that among high school students was

289

7.8% using IOTF, 5.5% using KCDC and 1.8% using WHO [48]. These findings show that the

290

WHO criteria now have a range for the definition of thinness.

291

Therefore, the use of the thinness criterion in the IOTF could be useful in population

292

enrollment for preventive measures. For this reason, our study is worthy as the first comparative

293

analysis on the prevalence of thin adolescents with scoliosis using three classifications. However,

294

this study has several limitations. First, some adolescents (27.9%) enrolled in the group with

295

scoliosis were diagnosed by physical examination but not confirmed using radiography.

296

Therefore, the 2.6% prevalence could be an overestimate. Second, no data were found regarding

297

the severity of scoliosis based on angle. Finally, because this study is a secondary data analysis, 13

298

only limited variables were selected; thus, there may be bias resulting from the selection.

299 300

Conclusion

301

A higher BMI was found to be protective against the development of AIS in both male and

302

female adolescents. AIS is frequently observed in female adolescents with a low BMI. Thus,

303

school nurses and healthcare professionals should pay close attention to thin female adolescents

304

to ensure early AIS management, as well as to adolescents with obesity to avoid missing the

305

curved spine. Our results demonstrate that the prevalence of low BMI in the population with

306

scoliosis differed depending on the thinness criteria. For female adolescents, the thinness cut-off

307

value based on the WHO criterion is too strict to screen populations at risk of scoliosis. The use

308

of IOTF thinness cut-off value could be useful in population enrollment for a preventive program.

14

309

Figure 1. Prevalence of Thinness among Adolescents with Scoliosis by BMI Criteria

310

BMI: body mass index

311

IOTF: Thinness grade 1 cut-off (BMI < 18.5 kg/m2) from the International Obesity Task Force

312

WHO: Thinness cut-off (BMI < -2SD) from the World Health Organization

313

KCDC: Wasting cut-off (BMI < 5th percentile) from the 2007 Korean National Growth Charts

314 315 316 317

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Table 1. Scoliosis by Individual Characteristics (N=16,412) Characteristics, N (%) Total Sex Male Female Grade Seventh Tenth BMI Thinness Normal Overweight/obesity Exercise < 3 days 3 days or more Duration of sleep < 6 hours 6 hours or more

x2

Total 16,412 (100)

Normal 15,978 (97.4)

Scoliosis 434 (2.6)

8430 (51.4) 7982 (48.6)

8297 (98.4) 7681 (96.2)

133 (1.6) 301 (3.8)

76.61 <.001

7395 (45.1) 9017 (54.9)

7260 (98.2) 8718 (96.7)

135 (1.8) 299 (3.3)

35.06 <.001

1028 ( 6.3) 10764 (65.6) 4620 (28.2)

973 (94.6) 10440 (97.0) 4565 (98.8)

55 (5.4) 324 (3.0) 55 (1.2)

72.76 <.001

11464 (70.1) 4888 (29.9)

11138 (97.2) 4780 (97.8)

326 (2.8) 108 (2.2)

5.34

.021

4047 (24.7) 12310 (75.3)

3919 (96.8) 12004 (97.5)

128 (3.2) 306 (2.5)

5.41

.020

BMI: body mass index from IOTF (International Obesity Task Force) criteria

P

Table 2. Associated Factors of Scoliosis by Sex Characteristics Grade Seventh Tenth BMI Normal Thinness Overweight/obesity Exercise < 3 days 3 days or more Duration of sleep < 6 hours 6 hours or more

Female (n=7,982) OR (95% CI) P

Male (n=8,430) OR (95% CI) P

1 1.68 (1.29-2.18)

<.001

1 2.21 (1.47-3.32)

<.001

1 1.89 (1.35-2.65) 0.42 (0.28-0.62)

<.001 <.001

1 1.36 (0.74-2.50) 0.51 (0.33-0.78)

.326 .002

1 1.06 (0.78-1.45)

.692

1 1.17 (0.82-1.66)

.387

1 1.16 (0.88-1.51)

.290

1 0.89 (0.59-1.35)

.588

BMI: body mass index from IOTF (International Obesity Task Force) criteria; CI = confidence interval; OR = odds ratio;

Table 3. Odds Ratio on Scoliosis by BMI criteria a IOTF OR (95% CI)

WHO OR (95% CI)

KCDC OR (95% CI)

Female (n=7,982) Normal Thinness Overweight/obesity

1 1.91 (1.36-2.68) 0.42 (0.28-0.62)

1 2.34 (1.20-4.55) 0.39 (0.27-0.56)

1 2.44 (1.69-3.52) 0.42 (0.29-0.61)

Male (n=8,430) Normal Thinness Overweight/obesity

1 1.34 (0.73-2.47) 0.51 (0.33-0.78)

1 1.40 (0.56-3.50) 0.53 (0.35-0.79)

1 1.46 (0.83-2.58) 0.51 (0.31-0.83)

Characteristics

IOTF: Thinness grade 1 cut-off (BMI < 18.5 kg/m2) from the International Obesity Task Force; WHO: Thinness cut-off (BMI < -2SD) from the World Health Organization; KCDC: Wasting cut-off (BMI < 5th percentile) from the 2017 Korean National Growth Charts; CI = confidence interval; OR = odds ratio a

Adjusted for grade