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Altered Disc Compression in Children With Idiopathic Low Back Pain: An Upright Magnetic Resonance Imaging Backpack Study

Shymon, Stephen J. BA*; Yaszay, Burt MD; Dwek, Jerry R. MD; Proudfoot, James A. MSc§; Donohue, Michael PhD§,¶; Hargens, Alan R. PhD*

doi: 10.1097/BRS.0000000000000114
Diagnostics

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

In normal children, common backpack loads compress all the lumbar intervertebral discs (IVDs). Under similar conditions, children with idiopathic low back pain (ILBP) experience less lumbar IVD compression, only at L5–S1, and more pain in response to increasing load. These findings suggest altered mechanisms for load tolerance in children with ILBP.

*Department of Orthopaedic Surgery, University of California, San Diego, CA

Rady Children's Hospital and Health Center, Department of Orthopaedic Surgery, San Diego, CA

Department of Radiology, Rady Children's Hospital and Health Center, University of California, San Diego, CA

§University of California, Clinical and Translational Research Institute, Biostatistics Core, San Diego, CA

University of California, Division of Biostatistics and Bioinformatics, San Diego, CA.

Address correspondence and reprint requests to Alan R. Hargens, PhD, Department of Orthopaedic Surgery, University of California, San Diego, UCSD Medical Center, 350 Dickinson Street, Ste 121, Mail Code 8894, San Diego, CA 92103-8894; E-mail: ahargens@ucsd.edu

Acknowledgment date: July 2, 2013. Revision date: October 3, 2013. Acceptance date: October 29, 2013.

The manuscript submitted does not contain information about medical device(s)/drug(s).

NASA grants NNX10AM18G and NNX13AJ12G, and the UCSD Clinical Translational Research Institute fellowship award funds were received in support of this work. The project described was partially supported by the National Institutes of Health, Grant UL RR031980 for years 1 and 2 of CTSA funding and/or UL1TR000100 during year 3 and beyond of CTSA funding.

Relevant financial activities outside the submitted work: consultancy, grants, payment for lecture, royalties, travel/accommodations/meeting expenses, employment.

© 2014 by Lippincott Williams & Wilkins