Non-specific low back pain: cross-sectional study of 11,423 children and youth and the association with the perception of heaviness in carrying of schoolbags

Participants

The study included Polish children and youth aged from 10–19 years. To determine the size of the sample the formula was used: 10% of all students in selected major cities from eastern Poland. The sample size for the group was calculated from at least 9000 individuals, plus an extra 20% to account for expected loses, for a total of 10,800 children and youth (Suresh & Chandrashekara, 2012). A 2-stage sampling method was adopted to obtain a representative sample of schoolchildren. In the first stage, public schools from three levels of education (primary, lower-secondary and upper-secondary schools) were randomly selected from ten major cities from eastern Poland. In the second stage, particular classes were selected (stratified phase sampling) (Brown et al., 1999). Ultimately, the study included students from the 4th to 6th grade of primary school (children aged 10–13; mean body weight: 43.7 kg, mean height: 1.55 m), the 1st to 3rd grade of lower-secondary school (14–16 years; mean body mass: 56.3 kg, mean height: 1.68 m) and the 1st to 3rd grade of upper-secondary school (17–19 years; mean body mass: 62.2 kg, mean height: 1.72 m).

11619 participants accepted to respond to the questionnaire. Of those that responded, 196 were excluded for incomplete questionnaires. The final analysis included 11,423 questionnaires (6,252 from girls and 5,171 from boys), which constitutes 98.3% of the total number of participants.

This was a cross-sectional study, approved by the Senate Research Ethics Committee (no. SKE 01-31/2012). The study was conducted in accordance with the Declaration of Helsinki. All the participants and their parents or guardians gave written informed consent.

Questionnaire

A questionnaire was applied as a research tool (File S2) (Kędra et al., 2019). The questionnaire was completed in the presence of one of the authors of the paper. While the participants filled out the survey, they were able to ask the author if they had any problems with the questionnaire. The survey was anonymous and voluntary.

The first part of the questionnaire was addressed to all respondents and concerned the following aspects: sex and date of birth, the perception of heaviness in carrying of schoolbag and information about experiencing LBP during the last year (12 months). Students who gave a negative response to this question about experiencing LBP did not complete the remaining part of the questionnaire. Individuals who declared that they had experienced LBP during the last year (12 months) answered the questions in the second part. The second part of the questionnaire included questions regarding the frequency of LBP, types of situations in which LBP occurred or increased, ways of coping with pain and suggestions of ways of reducing LBP. The region of LBP was explicitly described through a diagram in the questionnaire.

LBP was assessed using the following question: “Have you experienced low back pain within the last year (12 months)?”. The answer options were: “no”, “yes”, “yes, but only during menstruation”. “Yes” was considered to denote the presence of LBP.

The reliability of the questionnaire was assessed. The Kappa coefficient value for all the analysed variables was equal to or higher than 0.91 (Kędra et al., 2019).

After consulting the school doctor, students with such spinal diseases which may cause LBP as Scheuermann’s disease, spondylolysis, spondylolisthesis, rheumatic diseases, tumours, sarcomas⁵ were excluded from the study (23 students). In the case of the girls, those who experience LBP only during menstruation were also excluded.

Statistical analysis

Parameters were described using basic measurements of descriptive statistics for qualitative variables, i.e., percentage. Chi-square test was used to comparison of the prevalence of LBP taking into account sex and age. The association between the perception of heaviness in carrying of schoolbag and LBP outcome was analysed by univariate logistic regression with the odds ratio (OR) and 95% confidence interval (CI). Statistical significance was set at p < 0.05. The collected material was organised and analysed with the use of Statistica 13.3 calculation software by Statsoft (Poland).

Prevalence of NLBP

Among 11,423 of the respondents, 4,743 (41.5%) declared that they had experienced NLBP in the period of the last 12 months. Girls reported NLBP more often than boys (49.5% vs. 31.8%) (p < 0.001). The percentage of individuals reporting NLBP increased with age and this difference was statistically significant, p < 0.001 (Table 1).

Prevalence and circumstances of NLBP

The largest group was constituted by the respondents who experienced NLBP very rarely, i.e., 1–2 times a year (49.8% of the respondents). The analysis of the prevalence of NLBP with regard to sex revealed that boys declared rare pain (1–2 times a year) more often than girls (54.3% vs. 47.4%) (Table 2).

It can be noted that in the age groups of 10–13-year-olds and 14–16-year-olds, very rare pain (1–2 times a year) was reported more often than in the group of 17–19-year-olds (52.7% and 52.8% vs. 47.3%). In turn, the percentage of students reporting frequent or constant pain (occuring 1–2 times a month) was higher in the group of 17–19-year-olds than in the groups of 10–13 and 14–16-year-olds (12.4% vs. 11.3% and 11.3%) (Table 3).

While analysing the circumstances in which NLBP occurs with regard to the respondents’ sex, it can be concluded that both in the group of girls and among boys, the most common circumstances included lifting heavy objects (girls 58.2%, boys 43.9%), sitting (girls 50.6%, boys 47.9%), and carrying a school backpack (girls 43.2%, boys 33.6%) (Table 2). In the case of all the age groups (10–13 years, 14–16 years, 17–19 years), a considerable group of students declared that they felt NLBP during PE lessons (21.6% vs. 21.8% vs. 18.2%) (Table 3).

Ways of coping with NLBP

Rest (68.3%) and physiotherapeutic treatment other than electrotherapy (41.2%) were the most common ways of coping with NLBP in all respondents. The results indicate that an inconsiderable group of students (18.4%) sought doctor’s help due to NLBP (Table 2). The percentage of students seeking doctor’s help due to NLBP decreases with age (23.2% vs. 18.9% vs. 17.7%) (Table 3).

Over 16% of the respondents cope with NLBP by taking generally available painkillers. It can be noted that with age, the percentage of students who take painkillers to mitigate NLBP increases (10.6% vs. 13.3% vs. 18.9%) (Tables 2 and 3).

The respondents experiencing NLBP were asked what, according to them, can reduce the pain. The largest group was comprised of respondents who replied “Limiting the weight of a school backpack” (66.3%) and those who suggested increasing the level of physical activity (44.7%). According to a considerable group of students (42.9%), reducing the number of hours spent in a sedentary position might reduce NLBP (Table 2).

The prevalence of NLBP with regard to their perception of heaviness in carrying of schoolbags

Students (with and without NLBP) who declared that their school backpack was heavy constituted the highest percentage (55.4%). Students with NLBP declared that their school backpack was heavy more often than students without NLBP. Such a situation was noted in both sex groups and in all age groups. Girls with NLBP declared that their school backpack was heavy more often than boys with NLBP (65.2% vs. 52.1%). The analysis revealed that up to the age of 15, the percentage of students declaring that their school backpack was heavy was increasing (43.5% vs. 50.4% vs. 58.6%), and from the age of 16 was gradually decreasing (Table 4).

The perception of heaviness in carrying of schoolbags was a significant factor for NLBP. Students who thought that their backpacks weighed too much manifested a 1.44 times higher probability (95% Cl [1.33–1.55]) to develop NLBP. Girls who declared that their school backpack was heavy presented 1.36 times greater probability (95% Cl [1.23–1.51]) to develop NLBP than girls who declared that their school backpack was adequate. Boys manifested a 1.27 times higher probability (95% Cl [1.13–1.43]) to develop NLBP. In each age group, the declared heavy schoolbag is a risk factor for NLBP (Table 5).

Study limitations

The presented research used recognised methods of assessing LBP (Vikat et al., 2000; Wedderkopp et al., 2009; Heneweer, Vanhees & Picavet, 2009), but the obtained results are a subjective assessment of the reported NLBP.

The results of this study should be interpreted with caution because of its cross-sectional design. This evidence of itself is insufficient, but evidence from cross-sectional studies support the findings from prospective studies (Yamato et al., 2018). Perception of schoolbag weight is one of many aspects of schoolbag usage. Therefore, it is important to consider other factors related to the method of carrying the schoolbag that can affect LBP.

Study strengths

A large population sample (n = 11423) and a wide age range (10–19 years) constitute study strength as it makes it possible to illustrate the significance of the problem of NLBP in particular age groups. The reliability of the questionnaire applied in this study was assessed. The Kappa coefficient value for all the analysed variables was equal to or higher than 0.91, which indicates the reliability of information gathered with it. According to the authors’ knowledge, it is the first study regarding NLBP on such a large group of students from Poland. This study presents not only the frequency of pain, but also it describes an association between the perception of heaviness in carrying a schoolbag and LBP, which can facilitate the planning of preventive programs, quite different from those based on specific weight limits for schoolbags in children and youth.