|
David G. Wilder, Jae S. Lee, Malcolm H. Pope, Marianne
M. Magnusson, Vijay K. Goel
Iowa Spine Research Center, The University of Iowa, Iowa
City Iowa
Introduction: The frequency of low back complaints as well
as disabilities appears to be increasing. suggestive evidence
exist that industrialized environments may be of significance.
The Centers of Disease Control concur that back and vertebrogenic
pain may be associated with postural demands. One method used
to try to prevent back trouble involves use of circumferential
supports. Back supports have historically enjoyed great acceptance
by physicians. Recently lifting belts, or more properly, back
supports, have been widely promoted as a prevention for both
primary and secondary low back pain.
This study evaluated the erector spinae muscle response to
sudden unexpected loads in order to test the function of various
conditions of back support in affecting the muscle response to
sudden loads. Special consideration was given to the biomechanical
differences between the devices and their method of use.
Methods: Twenty subjects (ten males, ten females) with no
history of neuromuscular disease were tested for response to
a load suddenly and unexpectedly applied to a pan held in their
hands. Response of the erector spinae muscle group opposite the
dominant hand, at the L3 level to 3cm lateral to the midline
was monitored by surface electrodes. Surface EMG obtained during
dynamic conditions (isotonic, eccentric, concentric or isokinetic
muscle contractions) do not have features of the same scale and
the statistical characteristic of the signal changes over time.
Wavelet transform was, therefore, applied to the unprocessed
EMG signal to determine temporal information extraction. Load
was applied using a tennis ball weighted with lead shot, dropped
from a height even with the top of the subjects head, into an
instrumented hand-held pan. The six interventions were as follows:
1) No support worn (neutral control condition)
2) A Lumbar Lock® Back Support (Chase Ergonomics®
Inc.) worn high, bridging the pelvis and rib cage.
3) A Lumbar Lock Back Support worn loosely, low around the
pelvis (the support was placed such that its upper border was
2.5cm below the navel.
4) A sacroiliac (SI) belt worn according to the manufacturer's
instructions.
5) A Lumbar Lock Back Support worn proper, snugly around the
pelvis according to the manufacturer's instructions (the support
was placed such that its upper border was 2.5cm below the navel)
6) A second, no-support condition (neutral control condition)
Results: Normalized responses were analyzed using a repeated-measures
analysis of variance (ANOVA). Previous work by Marras et al has
shown that muscles over compensate by 70% when a load is caught
in the hands and no support is used. While all of the support
conditions in this study significantly affected how the males
responded to an unexpected load, both males and females over
compensated the least with a Lumbar Lock® Back Support worn
properly in a snug position around the pelvis (46% less over
compensation in women, 39% in men)
Conclusion: The significance of this study lies in its ability
to test a strategy for prevention of low back pain by the focus
on load reduction through an orthosis (lumbar support). Its effects,
to some degree, can be minimized through passive control systems,
as opposed to factors which are less controllable (for example,
spinal anatomy). Manning et al has attributed 12% of low back
problems to unexpected loads. Interventions that can reduce the
degree of over compensation during these situations can provide
great benefit as preventive measures and engineering controls.
"Low back pain is the leading cause of industrial
disability payments. The cost of lost wages alone comes to nearly
four billion dollars. Hence, even partial solutions to the low
back pain problem could provide significant society benefits.
While there has been much criticism of back supports and further
work is needed to confirm the cost benefit ratio, this study
suggests that a significant number of low back pain problems
attributed to sudden unexpected loads could be avoided by wearing
a properly fitted back support snugly around the hips".
Presented at the European Spine Society 8th Annual Meeting,
September, 1997, Kos, Greece.
|
