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


Spine. 2010;35(1):83-88. 

In This Article

Materials and Methods

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 imaged for the first time by an upright MRI scanner (FONAR Upright MRI, Melville, NY). Three boys and 5 girls, aged 11 ± 2 years (mean ± SD) were recruited by flyer distribution at local schools. Inclusion criteria were healthy children aged 9 to 14 with no history of back pain, scoliosis, or spine surgery. Written child assent and parental informed consent were obtained per UCSD IRB guidelines. Subjects weighed 44 ± 9 kg (mean ± SD) and were all between age-adjusted 25th and 75th percentiles for height and weight.

After resting for 30 minutes supine, subjects underwent sagittal T2 scans of the lumbar spine first supine, then standing. A Jansport backpack (San Leandro, CA) loaded with 4 kg of ceramic tiles was then placed on the subject's shoulders in the standard, 2-strap condition, and sagittal T2 scans were repeated. The subject then repeated the measurements with 8 kg and 12 kg backpack loads. These loads represented approximately 10%, 20%, and 30% body weight for our sample population. The empty backpack weighed approximately 500 g.

Lumbar disc height on midline sagittal T2 images was defined as the average of anterior and posterior disc heights.[10] Data are presented in terms of compressibility, defined as postloading disc height minus supine disc height.[7] Lumbar lordosis was defined as the sagittal Cobb angle between the superior endplates of S1 and L1.[7] Lumbar asymmetry was defined as the coronal Cobb angle between the superior endplates of S1 and L1. Distances and angles were measured twice by a radiologist, and the 2 results were averaged. There was never a difference between the 2 results of >10%.

To compare loading among all 6 lumbar discs under study, a 6 × 4 (6 discs × 4 loading conditions) repeated measures analysis of variance (ANOVA) was performed, and significance was set at P < 0.05. A 1 × 4 one-way ANOVA was performed for lordosis and asymmetry data and significance was set at P < 0.05. Recumbent data for compressibility, lordosis, asymmetry, and pain were not included in ANOVA analysis in order to isolate the effects of load on disc height and spinal curvature. All pairwise comparisons were adjusted for multiple comparisons using the Sidak test and a P-value of P < 0.05. A priori and post hoc power calculations were performed with G*Power[11] and all other statistical analyses were performed with SPSS software (SPSS, Chigago, IL).


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