Altered disc compression in children with idiopathic low back pain: an upright magnetic resonance imaging backpack study

Abstract

Study design: This study is a repeated measures design to measure the lumbar spine's response to common backpack loads in children with idiopathic low back pain (ILBP) using upright magnetic resonance imaging (MRI).

Objective: The purpose of this study is to analyze the lumbar spine's response to backpack loads with upright MRI in children with ILBP to compare their results with previously published normal child data under the same conditions. We hypothesize that typical backpack loads will have a different effect on the lumbar spine of normal children and children with ILBP.

Summary of background data: Research in normal children shows that backpack loads compress the lumbar intervertebral discs (IVDs), increase lumbar coronal deformity, and increase pain.

Methods: Fifteen pediatric and adolescent patients with ILBP were selected. Patients were excluded if a spinal deformity, an underlying pathology, or known injury was identified. A 0.6-T upright MRI scanner imaged the subjects while in supine and standing positions wearing 0-kg, 4-kg, and 8-kg backpacks. IVD height, lumbar lordosis, lumbar coronal deformity, and pain score were recorded after each condition and compared using analysis of variances. We compared the above-mentioned variables between ILBP and normal subjects using generalized least squares models.

Results: The cohort's mean age was 13 ± 3 years. The 4-kg and 8-kg backpacks only compressed the L5-S1 IVD relative to upright with no load. Subjects experienced increasing pain with increasing load. Load had no effect on lumbar lordosis or lumbar coronal deformity. Compared with normal children, children with ILBP experience significantly less disc compression at T12-L1 to L4-L5, less lumbar lordosis, and more pain with increasing load.

Conclusion: In children with ILBP, increasing backpack load compresses only the L5-S1 IVD. Compared with normal children, children with ILBP experience less lumbar IVD compression, less lumbar lordosis, and more pain due to increasing load suggesting altered mechanisms for load tolerance in children with ILBP.

Level of evidence: 3.

Figure 1

Midsagittal upright MR image of subject while wearing 4 kg backpack. Anterior and posterior intervertebral disc (IVD) height as well as the angle of lumbar lordosis are labeled. “A” stands for anterior and “P” stands for posterior.

Figure 2

The 4 kg and 8 kg backpacks significantly compress the L5-S1 disc compared to the upright condition (* p < 0.05).

Figure 3

The 4 kg backpack significantly compresses the anterior L5-S1 disc compared to the upright condition (* p < 0.05).

Figure 4

Increasing backpack loads did not significantly change lumbar asymmetry in relation to the upright condition.

Figure 5

Increasing backpack load did not significantly change lumbar lordosis in relation to upright condition.

Figure 6

The 4 kg and 8 kg backpacks significantly increased pain in comparison to the upright condition (* p < 0.05).