The Effect of Backpacks on the Lumbar Spine in Children: A Standing Magnetic Resonance Imaging Study

Timothy B. Neuschwander, MD; John Cutrone, MD; Brandon R. Macias, BA; Samantha Cutrone; Gita Murthy, PhD; Henry Chambers, MD; Alan R. Hargens, MD

Disclosures

Spine. 2010;35(1):83-88. 

In This Article

Abstract and Introduction

Abstract

Study Design: This study is a repeated measures design to measure the lumbar spine response to typical school backpack loads in healthy children. The lumbar spine in this setting was measured for the first time by an upright magnetic resonance imaging (MRI) scanner.
Objective: The purpose of this study is to measure the lumbar spine response to typical school backpack loads in healthy children. We hypothesize that backpack loads significantly increase disc compression and lumbar curvature.
Summary of Background Data: Children commonly carry school backpacks of 10% to 22% bodyweight. Despite growing concern among parents about safety, there are no imaging studies which describe the effect of backpack loads on the spine in children.
Methods: Three boys and 5 girls, age 11 ± 2 years (mean ± SD) underwent T2 weighted sagittal and coronal MRI scans of the lumbar spine while standing. Scans were repeated with 4, 8, and 12 kg backpack loads, which represented approximately 10%, 20%, and 30% body weight for our sample. Main outcome measures were disc compression, defined as post- minus preloading disc height, and lumbar asymmetry, defined as the coronal Cobb angle between the superior endplates of S1 and L1.
Results: Increasing backpack loads significantly compressed lumbar disc heights measured in the midline sagittal plane (P < 0.05, repeated-measures analysis of variance [ANOVA]). Lumbar asymmetry was: 2.23° ± 1.07° standing, 5.46° ± 2.50° with 4 kg, 9.18° ± 2.25° with 8 kg, and 5.68° ± 1.76° with 12 kg (mean ± SE). Backpack loads significantly increased lumbar asymmetry (P < 0.03, one-way ANOVA). Four of the 8 subjects had Cobb angles greater than 10° during 8-kg backpack loads. Using a visual-analogue scale to rate their pain (0-no pain, 10-worst pain imaginable), subjects reported significant increases in back pain associated with backpack loads of 4, 8, and 12 kg (P < 0.001, 1-way ANOVA).
Conclusion: Backpack loads are responsible for a significant amount of back pain in children, which in part, may be due to changes in lumbar disc height or curvature. This is the first upright MRI study to document reduced disc height and greater lumbar asymmetry for common backpack loads in children.

Introduction

Over 92% of children in the United States carry backpacks that are typically loaded with 10% to 22% body weight.[1,2] Thirty-seven percent of children aged 11 to 14 years report back pain, the majority of whom attribute their pain to wearing a school backpack.[3] Previous studies in children with 10%, 20%, and 30% body weight loads indicate that these loads generate very high contact pressures under backpack straps as well as significant pain.[4]

Despite growing parental concern regarding heavy backpack loads in schoolchildren and their association with childhood back pain, there are no known radiographic studies of the pediatric spine response to backpack loads.[5] Radiation risk to normal subjects from detailed roentgenographic or computed tomography analysis has precluded such studies, and the current data set is limited to estimates made with anatomic markers.[5,6] Only a biplane radiographic vertebral analysis can appropriately describe changes in disc height, lumbar lordosis, and spinal asymmetry. There are several radiographic studies describing the effects of axial loading in the adult[7,8] and pediatric spine.[9] These studies compare supine and simulated upright lumbar spine loading but do not describe the increased loads caused by typical school backpack loads in children. A new standing magnetic resonance imaging (MRI) imaging device permits detailed radiographic analysis of the lumbar spine response to backpack loads without risk of radiation.

The purpose of this study is to measure lumbar disc compressibility and lumbar spine curvature in response to school backpack loads in children. We hypothesize that typical school backpack loads significantly decrease lumbar disc height and increase lumbar curvature.

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