Research Review By Dr. Jeff Muir©

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Date Posted:

April 2021

Study Title:

The association between the weight of schoolbags and low back pain among schoolchildren: A systematic review, meta‐analysis and individual patient data meta‐analysis

Authors:

Calvo‐Muñoz I, Kovacs FM, Roqué M, Seco‐Calvo J

Author's Affiliations:

Faculty of Health Sciences, Catholic University San Antonio, UCAM, Murcia, Spain; Spanish Back Pain Research Network, Madrid, Spain; Unidad de la Espalda Kovacs, Hospital Universitario de Moncloa, Madrid, Spain; Iberoamerican Cochrane Centre, Biomedical Research Institute Sant Pau (IIB Sant Pau), Barcelona, Spain; CIBER Epidemiología y Salud Pública (CIBERESP), Madrid, Spain; Institute of Biomedicine (IBIOMED), University of León, León, Spain; University of the Basque Country, Leioa, Spain

Publication Information:

European Journal of Pain 2020; 24(1): 91-109.

Background Information:

Low back pain remains a major health and socioeconomic burden and is one of the main causes of years lived with disability worldwide (1). Associated costs in the United States alone are estimated at $100 billion annually (2)!

While predominantly thought of as a condition affecting adults, low back pain (LBP) among school-aged children is, in fact, higher than previously thought, with a lifetime prevalence of 47% by age 14 (3-5). Additionally, adolescent LBP is a risk factor for LBP in adulthood (6). The causes of adolescent LBP are multifactorial and include biological, psychosocial and lifestyle-related variables, although the evidence currently available in the literature is somewhat inconsistent.

One causal factor that warrants investigation is the weight of schoolbags that children carry to school. Indeed, over 80% of schoolchildren reporting LBP attribute their pain to heavy schoolbags (7). The goal of this study was to estimate whether carrying a schoolbag heavier than advised (i.e. > 10% of bodyweight) is associated with a higher prevalence of LBP in children between the ages 9 and 16. The authors performed a systematic review of the literature and a meta-analysis of available data, including an individual participant data (IPD) analysis.

Pertinent Results:

Eligible Studies:
84 studies were eligible for full-text review, of which 21 (all cross-sectional studies) were included in the systematic review (sample size: 18296 participants); 11 (9188 participants) were included in the meta-analysis; and 7 (8218 participants) were included in the IPD analysis.

Systematic Review:
Included studies were of moderate to high methodological quality, with an average score of 78.3% (range: 55-100%).

Meta-Analysis:
The meta-analysis failed to identify a significant association between carrying schoolbags > 10% of bodyweight and LBP prevalence (OR = 1.06 [95% HKSJ CI]: 0.94-1.20; I2 = 0%; 11 studies, 10087 participants; "low" certainty of evidence). No association was noted when adjusted (OR = 0.95 [95% HKSJ CI]: 0.86-1.05) and unadjusted results (OR = 1.13 [95% HKSJ CI]: 0.91-1.40) were compared.

IPD Meta-Analysis:
When a sub-group meta-analysis was completed, using age to stratify studies, non-significant differences were noted between children ≤ 12 yoa vs. ≥ 13 yoa (Chi2 = 2.88, df = 1 [p = 0.09], I2 = 65.2%).

A second sub-group analysis using sports activity as a variable did not predict LBP, i.e. whether the participants did or did not participate in sports did not impact LBP prevalence (Chi2 = 0.52, df = 1 [p = 0.47], I2 = 0%).

Clinical Application & Conclusions:

The authors concluded, based on their meta-analysis, that carrying schoolbags heavier than the prescribed limit (i.e. > 10% of bodyweight) was not associated with a higher prevalence of LBP in children aged 9-16 yrs. They caution, though, that this conclusion is based on cross-sectional data and future research from studies of higher levels of evidence may warrant modification of their conclusions.

EDITOR’S NOTE: I don’t think this means we shouldn’t discuss backpacks with parents and children, and it still seems reasonable to me that slugging a really heavy backpack around all day may not be great for kids. However, this study suggests that our long-held assumption about the causal relationship between the weight of a schoolbag and low back pain in children may be inaccurate. With the increasing prevalence of low back pain noted in this age bracket – maybe we should be looking for a different cause? Perhaps the accumulated stress of schoolbag weight doesn’t manifest in the lumbar spine until an individual is older? Further, perhaps schoolbag weight may relate to neck pain in schoolchildren…another prevalent condition in children and topic for another day...

Study Methods:

Searched databases included: CINAHL, Current Contents, EMBASE, Family health database, FSTA (Food Science and Technology Abstracts), ISI Web of Knowledge, LILACS, MEDLINE, NNNConsult, OvidMD, PEDro, ProQuest Central, PubMed, SciFinder Scholar, Science Direct, Scopus, SPORTDiscus, The Cochrane Library, Web of Science, and the Wiley Online Library. An additional search was conducted on the websites of journals that were thought to be likely to publish relevant articles, including: "Pain", "European Journal of Pain", "Clinical Journal of Pain", "Spine", "Spine Journal", "European Spine Journal", "Open Journal of Pediatrics", "European Journal of Pediatrics", "European Journal of Public Health", "Scandinavian J Public Health", "Ergonomics" and "Applied Ergonomics".

Relevant search terms included: “adolescent”, “children”, “schoolchildren”, “young”, “pediatric”, “back pain”, “low back pain”, “lumbar pain”, “prevalence”, “epidemiology“, “risk factors”, "schoolbags", “school bag“, "backpack", “carrying bag” and "bag".

Eligibility Criteria:
2 authors independently screened relevant articles, with a third reviewer independently screening citations where consensus could not be reached.

Specific eligibility criteria included:
  • Published observational studies focusing on risk factors for LBP, either cross-sectional or longitudinal in nature, including case-control studies and cohort studies,
  • Included ≥ 50 participants aged 9-16,
  • Examined the relationship between schoolbag weight as a proportion of bodyweight and LBP, and
  • No language or publication date restrictions.
Authors of eligible studies were contacted and asked to provide their datasets, with patient-identifying information removed. Received data was used to perform an individual patient data meta-analysis (IPD meta-analysis), where individual datasets were pooled. Variables:
Weight of schoolbags was categorized as “heavy” or “not heavy” based on definitions from the original studies. Covariates for the IPD meta-analysis included: age, gender and sporting activity.

Methodological Quality:
The Ottawa-Newcastle Scale (8) was used to evaluate methodological quality. Certainty of the evidence was evaluated using the GRADE system for studies on prognostic factors (9).

Statistical Analysis:
Odds ratios (ORs) and 95% confidence intervals (CI) were used to assess the association between schoolbag weight and LBP. The meta-analysis was conducted using a random effects model. For all data, including that from the IPD meta-analysis, ORs and CIs were converted post-hoc to the Hartung‐Knapp‐Sidik‐Jonkman method (10). Heterogeneity amongst studies was assessed through I2 (11). Two sub-group analyses were conducted using age and sports activity as variables. In the first sub-group analysis, participants were stratified based on age (< 12 or >13). In the second, participation in sports activities (yes/no) was the relevant variable.

Study Strengths / Weaknesses:

Strengths:
  • The authors employed a comprehensive search strategy, including secondary website searches for relevant articles.
  • The data analysis was strong, including IPD meta-analysis.
Weaknesses:
  • Only cross-sectional and cohort studies were included.
  • Only 7 studies were available for IPD meta-analysis.
  • The overall certainty of the evidence was low.

Additional References:

  1. Hoy D, March L, Brooks P et al. The global burden of low back pain: Estimates from the Global Burden of Disease 2010 study. Annals of the Rheumatic Diseases 2014; 73: 968–974.
  2. Dieleman JL, Baral R, Birger M et al. US spending on personal health care and public health, 1996–2013. JAMA 2016; 316: 2627–2646.
  3. Calvo‐Muñoz I, Kovacs FM, Roqué M, Gago Fernández I & Seco Calvo J. Risk factors for low back pain in childhood and adolescence: A systematic review. Clinical Journal of Pain 2018; 34: 468–484.
  4. Kamper SJ, Yamato TP, & Williams CM. The prevalence, risk factors, prognosis and treatment for back pain in children and adolescents: An overview of systematic reviews. Best Practice & Research Clinical Rheumatology 2016; 30: 1021–1036.
  5. Swain MS, Henschke N, Kamper SJ et al. An International survey of pain in adolescents. BMC Public Health 2014; 14:447.
  6. Hestbaek L, Leboeuf‐Yde C & Kyvik KO. Is comorbidity in adolescence a predictor for adult low back pain? A prospective study of a young population. BMC Musculoskeletal Disorders 2006; 7: 29.
  7. Skaggs DL, Early SD, D'Ambra P et al. Back pain and backpacks in school children. Journal of Pediatric Orthopedics 2006; 26: 358–363.
  8. Wells G, Shea B, O'Connell D et al. The Newcastle‐Ottawa Scale (NOS) for assessing the quality of nonrandomised studies in meta‐analyses. Ottawa, ON: Ottawa Hospital Research Institute 2009. Available: http://www.ohri.ca/progr ams/clini cal_epidemiology/oxford.asp.
  9. Huguet A, Hayden JA, Stinson J et al. Judging the quality of evidence in reviews of prognostic factor research: Adapting the GRADE framework. Systematic Reviews 2013; 2: 71.
  10. Inthout J, Ioannidis JPA & Borm GF. The Hartung‐Knapp‐Sidik‐Jonkman method for random effects meta‐analysis is straightforward and considerably outperforms the standard DerSimonian‐Laird method. BMC Medical Research Methodology 2014; 14: 25.
  11. Higgins JPT & Thompson SG. Quantifying heterogeneity in a meta‐analysis. Statistics in Medicine 2002; 21: 1539–1558.