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

Results

Disc Height Compression

Increasing backpack loads significantly compressed the T12-L1, L1-L2, L2-L3, L3-L4, L4-L5, and L5-S1 disc heights (Figure 1, P < 0.05, repeated measures ANOVA). In addition, the caudal lumbar discs were more compressible, with the L5-S1 disc about twice as compressible as the T12-L1 disc (Figure 1, P < 0.05, repeated measures ANOVA). Interaction between disc and load was nonsignificant, indicating that each disc responded to increasing loads similarly (P > 0.05, interaction between disc and load).

Figure 1.

Lumbar disc compressibility during backpack loading. Backpack loads of 4, 8, and 12 kg significantly compressed each disc (P < 0.05). Disc compressibility increased in the caudal lumbar discs (P < 0.05). Changes in compressibility (mm) are related to the control condition of supine posture.

With pairwise comparisons among discs, only 2 disc levels were significantly different, with L2-L3 significantly more compressible than L1-L2 (P < 0.05). With pairwise comparisons among loads, 4, 8, and 12 kg loads each caused significantly more disc compression than standing without a backpack load (P < 0.05), but differences among compression caused by each load were not significant. With pairwise comparisons between loads by disc, L4-L5 and L5-S1 demonstrated significant differences between standing and 4 kg loads, while L3-L4, L4-L5, and L5-S1 demonstrated significant differences between standing and 8 kg loads, and T12-L1, L3-L4, L4-L5, and L5-S1 demonstrated significant differences between standing and 12 kg loads. Disc level L3-L4 demonstrated a significant difference in compressibility between 4 kg and 12 kg loads.

As demonstrated in Table 1, backpack load correlated linearly with disc compressibility at each disc level, with r 2 ranging from 0.10 at T12-L1 and steadily increasing to 0.23 at L5-S1.

Lumbar Lordosis

Changes in lumbar lordosis were quite variable as children adjusted their posture to higher backpack loads (Figure 2). No significant changes in lumbar lordosis were seen in response to load (P = 0.767, 1-way ANOVA, post hoc power analysis = 0.35).

Figure 2.

Lumbar lordosis during backpack loading. The sagittal Cobb angle from the superior endplates of S1 and L1 was measured during all loading conditions. Backpack loads of 4, 8, and 12 kg did not significantly increase lumbar lordosis (P = 0.767, 1-way ANOVA). Lumbar lordosis was quite variable as children adjusted posture during each load.

Spinal Asymmetry

Backpack loads caused lumbar spinal asymmetry (Figure 3). The coronal Cobb angle from the superior endplates of S1 and L1 was measured during all loading conditions. Backpack loads of 4, 8, and 12 kg significantly increased lumbar asymmetry (P < 0.03, 1-way ANOVA). Four of the 8 subjects had Cobb angles greater than 10° during loading, and 1 subject had a Cobb angle of 21.1° (Figure 4) during the 8 kg load. Five subjects had a lumbar curve to the right, and 3 subjects had a lumbar curve to the left. All subjects maintained the same direction of curvature throughout the loading conditions. Although the correlation coefficient was small, lumbar asymmetry correlated linearly with backpack load (r 2 = 0.124, P = 0.015).

Figure 3.

Lumbar spinal asymmetry during backpack loading. Lumbar spinal asymmetry was assessed by coronal Cobb angle from the superior endplates of S1 and L1 during all loading conditions. Backpack loads of 4, 8, and 12 kg significantly increased lumbar asymmetry (P < 0.03, 1-way ANOVA).

Figure 4.

Example of lumbar asymmetry. Coronal T2 images demonstrating our most exaggerated example of backpack-induced lumbar asymmetry in a 9-year-old boy. A, Shows a child standing with no load. B, Shows a child standing with an 8-kg backpack load in the standard, 2-strap position. The Cobb angle from the superior endplate of S1 to the superior endplate of L1 in A is 0°. After loading (B), the Cobb angle increased to 21.1°.

Pain

Pain was associated with backpack loading (Figure 5). Using a visual-analogue scale to rate their pain (0-no pain, 10-worst pain imaginable), subjects associated backpack loads of 4, 8, and 12 kg with significant increases in back pain (P < 0.001, 1-way ANOVA). Pain was positively correlated with backpack load (r 2 = 0.711, P < 0.001).

Figure 5.

Pain during backpack loading. Backpack loads of 4, 8, and 12 kg significantly increased back pain (P < 0.001, 1-way ANOVA). Subjects rated their pain using a visual-analogue scale (0-no pain, 10-worst pain imaginable).

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