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SPINE Volume 35, Number 1, pp 83–88
©2009, Lippincott Williams & Wilkins
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,‡ and Alan R. Hargens, MD*
Study Design. This study is a repeated measures de-
sign 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 sig-
nificantly increase disc compression and lumbar curvature.
Summary of Background Data. Children commonly
carry school backpacks of 10% to 22% bodyweight. De-
spite growing concern among parents about safety, there
are no imaging studies which describe the effect of back-
pack 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 com-
pressed 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 in-
creases 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 sig-
nificant amount of back pain in children, which in part,
may be due to changes in lumbar disc height or curva-
ture. This is the first upright MRI study to document re-
duced disc height and greater lumbar asymmetry for
common backpack loads in children.
Key words: backpacks, children, disc compression,
spinal asymmetry. Spine 2010;35:83– 88
Over 92% of children in the United States carry back-
packs 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 stud-
ies 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 radio-
graphic studies of the pediatric spine response to back-
pack loads.
5
Radiation risk to normal subjects from de-
tailed roentgenographic or computed tomography
analysis has precluded such studies, and the current data
set is limited to estimates made with anatomic mark-
ers.
5,6
Only a biplane radiographic vertebral analysis can
appropriately describe changes in disc height, lumbar
lordosis, and spinal asymmetry. There are several radio-
graphic 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 mag-
netic resonance imaging (MRI) imaging device permits
detailed radiographic analysis of the lumbar spine re-
sponse 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.
Materials and Methods
This study is a repeated measures design to measure the lumbar
spine response to typical school backpack loads in healthy chil-
dren. 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. Writ-
From the *Department of Orthopaedic Surgery, University of Califor-
nia, San Diego, CA; †TrueMRI, San Diego, CA; and ‡Rady Children’s
Hospital, San Diego, CA.
Acknowledgment date: March 4, 2009. Revision date: May 8, 2009.
Acceptance date: May 11, 2009.
The manuscript submitted does not contain information about medical
device(s)/drug(s).
Other funds were received in support of this work. No benefits in any
form have been or will be received from a commercial party related
directly or indirectly to the subject of this manuscript.
Written child assent and parental informed consent were obtained per
UCSD IRB guidelines.
TrueMRI is a local imaging center that donated use of their upright
MRI. Fonar provided subject reimbursement.
Address correspondence and reprint requests to Timothy Neuschwan-
der, MD, Department of Orthopaedic Surgery, University of Califor-
nia, San Diego, 350 Dickinson St, Suite 121, Mail Code 8894, San
Diego, CA 92103; E-mail: tneuschwander@ucsd.edu
83
ten 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 percen-
tiles for height and weight.
After resting for 30 minutes supine, subjects underwent sag-
ittal 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 re-
peated. The subject then repeated the measurements with 8 kg
and 12 kg backpack loads. These loads represented approxi-
mately 10%, 20%, and 30% body weight for our sample pop-
ulation. The empty backpack weighed approximately 500 g.
Lumbar disc height on midline sagittal T2 images was de-
fined as the average of anterior and posterior disc heights.
10
Data are presented in terms of compressibility, defined as post-
loading 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,
a6⫻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, asymme-
try, 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 compari-
sons 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).
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, inter-
action between disc and load).
With pairwise comparisons among discs, only 2 disc
levels were significantly different, with L2–L3 signifi-
cantly 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 differ-
ences among compression caused by each load were not
significant. With pairwise comparisons between loads by
disc, L4–L5 and L5–S1 demonstrated significant differ-
ences 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 chil-
dren 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 1. Lumbar disc compress-
ibility during backpack loading.
Backpack loads of 4, 8, and 12 kg
significantly compressed each
disc (P⬍0.05). Disc compress-
ibility increased in the caudal
lumbar discs (P⬍0.05). Changes
in compressibility (mm) are re-
lated to the control condition of
supine posture.
Table 1. Linear Regression Between Disc Compression
and Backpack Load
Level r
2
P
T12–L1 0.10 P⫽0.045
L1–L2 0.12 P⫽0.03
L2–L3 0.11 P⫽0.036
L3–L4 0.15 P⫽0.017
L4–L5 0.22 P⫽0.004
L5–S1 0.23 P⬍0.003
Backpack loads of 4, 8, and 12 kg significantly increased back pain (P⬍0.001,
one-way ANOVA).
Subjects rated their pain using a visual-analogue scale (0-no pain, 10-worst
pain imaginable).
84 Spine •Volume 35 •Number 1 •2010
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 condi-
tions. 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 direc-
tion of curvature throughout the loading conditions. Al-
though the correlation coefficient was small, lumbar
asymmetry correlated linearly with backpack load (r
2
⫽
0.124, P⫽0.015).
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
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.
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).
85Spine Loading in Children •Neuschwander et al
backpack loads of 4, 8, and 12 kg with significant in-
creases in back pain (P⬍0.001, 1-way ANOVA). Pain
was positively correlated with backpack load (r
2
⫽
0.711, P⬍0.001).
Discussion
To our knowledge, this is the first upright MRI study to
demonstrate decreases in lumbar disc height and in-
creases in lumbar asymmetry due to typical school back-
pack loads in children.
Disc Compression
Kimura et al found decreases in L4–L5 disc height with a
50% body weight axial load, intended to mimic upright
posture.
7
These investigators found disc height changes
in the order of about 1 mm in the L4–L5 disc in young
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 Ais 0°. After loading (B),
the Cobb angle increased to 21.1°.
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).
86 Spine •Volume 35 •Number 1 •2010
adult subjects. Our results for L4–L5 disc compressibil-
ity from supine to upright posture in children are similar
(Figure 1). Macias et al found decreases in lumbar height
with supine axial loading, but individual disc heights did
not approach significance.
8
In a roentgenographic study
of normal adolescent spines, Reuben and associates were
unable to demonstrate a difference between standing and
supine intervertebral disc heights.
9
These authors mea-
sured the central vertebral disc height rather than the
commonly used Dabbs and Dabbs method.
10
Lordosis
Kimura et al found increases in lumbar lordosis at L3–L4
and L5–S1 with a 50% body weight axial load, which
was intended to mimic upright posture.
7
Macias et al
also found that axial loading in a supine MRI caused
increases in lumbar lordosis, measured from T12–L1 to
L5–S1.
8
Chow et al found decreases in lumbar lordosis
and increases in thoracic kyphosis with increasing load
due to backpack weight while standing.
5
Although our
comparable data are not significant, the trend is similar
to published data. We postulate that lordosis is de-
creased in supine posture and that lordosis increases with
standing and other axial loads. A backpack load is not an
axial load, however, and for the load to stay balanced
over the subject’s center of mass, thoracic kyphosis must
increase. This causes a lever-arm effect as flexion occurs
at the lumbar spine and lumbar lordosis decreases. Since
many of our subjects moved frequently to change the
load center of mass between image acquisitions, this may
have introduced variability in our data.
Asymmetry
Most children will carry their backpacks with both
straps,
3
but occasionally will carry their backpacks using
only 1 shoulder strap.
12
It has been established that
asymmetric load carrying in children due to using only 1
backpack strap likely contributes to low back pain.
6
Ne-
grini and Negrini found that the postural response to a
1-strap asymmetric backpack load was to elevate the
loaded shoulder and laterally deviate the trunk away
from the load so as to reposition the load over the sub-
ject’s center of mass.
13
They did not find lumbar asym-
metry with subjects wearing a pack in a 2-strap condi-
tion; however, anatomic markers were placed on the skin
overlying every other spinous process. Pascoe et al also
reported significantly increased lumbar asymmetry,
about 17° with a 1-strap condition, but no lumbar asym-
metry with a 2-strap condition.
12
Both studies used an-
atomic markers on the skin to quantify coronal asymme-
try. Chow et al found that increasing backpack load was
associated with increasing pelvic obliquity and rotation
in normal children and children with adolescent idio-
pathic scoliosis, but these investigators did not measure
the lumbar spine itself since their anatomic skin markers
that did not include the lumbar spine.
14
Studies with
anatomic skin markers are unable to measure true Cobb
angles and thus may not be able to detect lumbar spine
asymmetry. A recent study found asymmetric load dis-
tribution in children wearing backpacks with both straps
adjusted to equal length, with children tending to load
the right shoulder significantly more than the left.
15
Asymmetric loading was not associated with handed-
ness; this latter study had a small sample size.
Our study found that asymmetry increased with
weight up to the 8 kg load, but subsequently decreased
with the 12 kg load. Subjectively, we noted that our
subjects could tolerate the 8 kg load with minimal pos-
tural adjustment. With the 12 kg load, however, most
subjects attempted to readjust both posture and load be-
fore imaging. As with all loading conditions, subjects
carried the load in the standard, 2-strap condition.
Pain
Correlating back pain with load was not a principal hy-
pothesis of our study, and as such, we did not randomize
loads. Thus, the linear correlation between pain and
backpack load (r
2
⫽0.711, P⬍0.001) in this study may
be a result of subjects’ awareness of increasing load.
However, the correlation between back pain and back-
pack load is well-documented in the literature. A cross-
sectional study of children from the metropolitan Los
Angeles area found that heavier school backpack loads
correlated with back pain.
3
In a recent review on school
backpacks, Mackenzie et al summarized the following as
risk factors for low back pain in schoolchildren: female
gender, poorer general health, high levels of physical ac-
tivity (including sports competition), time spent sitting,
heavier backpack loads, greater time spent carrying a
backpack, low physiologic maximum lumbar spine mo-
bility, and a family history of back pain.
16
It is suggested
that psychological factors play a role in low back pain
occurrence in children.
17
Individuals with low back pain
during childhood and family history of back pain have
an 88% chance of developing low back pain as adults.
18
Limitations
Our study has some limitations. A lumbar coil was used
to image the lumbar spine. Because the entire spine was
not imaged, coronal measurements did not accurately
reflect a true scoliosis measurement, since the apex and
endpoints of the curve were not identified. The coronal
Cobb angles measured in this study likely underestimate
the true coronal curvature of the spine under load. In
addition, our study did not control for time of day, since
the spinal column shortens throughout the day.
19
Each
of our subjects had been ambulatory for at least an hour
before the required 30-minute of supine rest. Since most
of the daily disc height decrease occurs during the first
hour after rising, the required supine rest period likely
imposed some uniformity on the disc heights.
20
It would
have been difficult to impose a longer period of rest on
our sample population. The amount of time our subjects
experienced load may underestimate the amount of time
per day that children typically wear backpacks. Packs
were worn for approximately 10 minutes at each load for
a total of about 30 minutes, whereas children typically
carry backpacks for between 30 and 60 minutes per
87Spine Loading in Children •Neuschwander et al
day.
21
However, our loading times were contiguous
whereas children typically wear their backpacks inter-
mittently throughout the day. Since backpack loading
induced coronal asymmetry, midline sagittal disc heights
may have been oriented obliquely to the perpendicular
axis. It is possible that we overestimated postloading disc
height and therefore underestimated disc compression.
Finally, our pain data were not specific to low back pain
and likely captured shoulder, thoracic, and lumbar pain
caused by the pack.
This study is the first radiographic analysis to describe
the lumbar spine in children wearing backpacks. Lumbar
asymmetry induced by backpack loading is a new and
unexpected finding. Low back pain in children may be
worsened by discogenic or postural changes. Future
studies should be directed at upright MRI analyses of
spine loading in children with idiopathic low back pain
and compared with the present study of normal children.
Key Points
●Typical school backpack loads significantly com-
pressed lumbar disc heights in children.
●Typical school backpack loads significantly in-
creased lumbar asymmetry.
●Children reported significant increases in back
pain associated with backpack loads.
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88 Spine •Volume 35 •Number 1 •2010
