Biomechanical Comparison
of the Milwaukee Brace
(CTLSO) and the TLSO for
Treatment of Idiopathic
scoliosis
Avinash G. Patwardhan, PHD
Thomas M. Gavin, CO
Wilton H. Bunch, MD, PHD
Victoria M. Dvonch, MD
Ray Vanderby Jr., PHD
Kevin P Meade, PHD
Mark Sartori
ABSTRACT
The decision to choose between a CTLSO
(Milwaukee brace) and a TLSO (such as
the Boston system, Wilmington, Miami or
Rosenberger orthosis) is affected by several factors including cosmesis, geographical preference and popularity of a given
orthosis. Performance usually is a secondary consideration since objective comparisons have been difficult.
A finite element model was used to
quantify and compare the effects of the
CTLSO and TLSO in increasing spinal
stability as measured in terms of the critical load of right primary thoracic with
left lumbar compensatory and left primary lumbar with right compensatory
idiopathic scoliotic curves.
While the CTLSO and TLSO were
equal in stabilizing lumbar primary
curves, the TLSO was 25 percent less effective in stabilizing primary thoracic
curves. Pad and counterforce placement
were critical factors influencing stability
for both the CTLSO and TLSO, demonstrating the importance of proper initial fit and timely growth adjustments to
ensure proper pad placement throughout the duration of wear.
Key Words: Idiopathic Scoliosis, Milwaukee Brace, TLSO, Orthotic Stabilization, Biomechanics.
Introduction
Several different orthoses currently are
available for nonoperative treatment of
idiopathic scoliosis (1). The Milwaukee
cervico-thoraco-lumbo-sacral orthosis
(CTLSO) (see Figure 1
) is the traditional standard and has a well-documented history of results (2-6). During
the 1970s, low-profile or "underarm-type" orthoses were developed to treat
lumbar and thoracolumbar curves (see
Figure 2
) (7-10). Known as thoracolumbo-sacral orthoses (TLSOs), they
were later advocated to treat curves
with thoracic primary curves (1).
The decision regarding whether to
use a TLSO or a CTLSO is primarily
based on cosmesis, preference of a given orthosis in certain geographic areas
and popularity of a specific orthotic
technique (such as the part-time criteria of the Charleston TLSO).
The TLSO is a more cosmetically appealing orthosis since it can be easily
concealed by clothing, unlike the
CTLSO, which has a neck ring that
protrudes above clothing. Recent developments of the low-profile neck ring
have attempted to address this cosmetic concern.
In certain regions of North America,
specific types of orthoses are geographically preferred because of variation in
orthotic training between regions
where specific TLSOs were developed.
A few areas still prefer the CTLSO in
spite of the unsightly superstructure
and neck ring, whereas TLSOs, such as
the Miami orthosis, are preferred in
much of the Southeast (the geographic
region of its originators). The Boston
TLSO system is preferred in the Northeast for the same reason.
Despite the void of longitudinal
studies, the Charleston TLSO has become popular nationwide because it is
cosmetically appealing and is prescribed for night-time wear only, allowing patients to be out of the orthosis
during waking hours.
Mechanical performance has not
been a primary factor in deciding which
orthosis to use for idiopathic scoliosis.
While several types of orthoses exist,
they all function by the same mechanisms of action: endpoint control,
curve correction and continuous transverse support. Endpoint control prevents sway of the vertebral column and
reduces gross trunk motion while lumbar and thoracic pads reduce scoliotic
curves and maintain curve reduction
for the duration of wear, providing
continuous lateral support at the apex
of the reduced curve. The synergistic
effects of endpoint control, curve correction and continuous lateral support
in orthotic stabilization of scoliotic
curves with a biomechanical model
have been demonstrated in previous
studies (11,12).
While the mechanisms of action of the
CTLSO have been investigated experimentally (13,14) and with finite element
models (15), little is known about the
TLSO's mechanisms of action. There are
no objective data on the effects of trimline height and pad placement on curve
correction and stability achieved by a
TLSO. As a result, objective comparisons of the effectiveness of the CTLSO
and TLSO in treating different curve
patterns have not been possible.
This study was designed to test the
primary hypothesis that the CTLSO is
superior to the TLSO in stabilizing primary thoracic idiopathic scoliotic
curves and the secondary hypothesis
that proper pad placement is essential
in providing optimum curve stability
with the CTLSO and TLSO.
Methods
A finite element model of the spine-orthosis system was used to evaluate the
stability of spinal curves for a variety of
conditions. This mathematical computer model is capable of analyzing spinal
geometries and response to load and
was validated from patient radiographs. The model allowed simulation
of different curve geometries and variation of orthotic design parameters
such as pad placement and trimline location relative to the curve apices and
endpoints. These simulation studies are
useful in identifying, for each curve pattern, the optimum placement of pads
and trimline for the most stable curve,
i.e., one that can support the most axial
load without progressing.
Type of Curves Analyzed
The stabilizing effect of an orthosis was
studied for two combined thoracic and
lumbar curve patterns: a 35-degree primary right thoracic curve with a 20-degree compensatory left lumbar component and a 35-degree primary left lumbar curve with a 20-degree compensatory right thoracic component (see
Table A
).
These two curve patterns will be referred to in this article as the primary
thoracic curve and the primary lumbar
curve, respectively. The compensatory
component was assumed to be twice as
flexible as the primary component. This
is consistent with clinical observations
of curve correction seen in the primary
and compensatory components upon
lateral bending (16).
Biomechanical Model
A finite element model of the spine
was used to simulate the response of
the curve in the frontal plane to external loads. Each motion segment of the
thoracolumbar spine (T1-sacrum) was
modeled as a beam element with end
nodes located at the centroids of adjacent vertebral bodies. Similar models
have been used in previous studies of
scoliosis (17,18).
The flexural rigidities of the beam elements were chosen based on stiffness
identification made with the same type
of spine model (17) and are comparable to data reported in the literature
(13,19). Nonlinear effects due to large
displacements were incorporated in the
model by updating the geometry and
global stiffness matrix at each incremental load step.
The effect of the pelvic interface on
the CTLSO was simulated by constraining all degrees of freedom of the
sacrum. Since the neck ring keeps the
head and neck centered over the pelvis,
the first thoracic vertebra was constrained from moving in the lateral direction. However, the T1 vertebra was
not constrained in the inferior-superior
direction and was allowed to rotate in
the frontal plane.
The model parameters of the TLSO
used in this study are consistent with
the clinical parameters of a well-fitted
Rosenberger, Boston or Miami orthosis
(see Figure 2
). These TLSOs rely on the
use of a trimline on the concavity of the
primary curve to provide a counterforce that, in conjunction with the lateral pad loads, provides the triangulated force system to correct and stabilize
the curve.
In the TLSO model, the sacrum was
fixed to simulate the stabilizing effect
of the pelvic section of the orthosis, exactly like the Milwaukee brace. The
trimline of a TLSO provides lateral
support to the ribs. As the ribs are
pushed against the trimline due to pad
loads, the stiffness of the trimline-rib
complex provides resistance to lateral
displacement of the curve. The equivalent stiffness of the trimline-rib complex was simulated by linear springs
along the medial-lateral degree of freedom at appropriate vertebral levels.
The values of spring constants were derived using the data reported by Agostoni et al. (20) and Andriacchi et al. (21).
Since a TLSO imposes no kinematic
constraints on the first thoracic vertebra, T1 was not constrained in the medial-lateral and inferior-superior directions and was allowed to rotate in the
frontal plane.
To simulate the effect of the CTLSO
on the correction and stability of primary thoracic curves, axillary sling
forces must be considered in addition
to the thoracic and lumbar pad forces
(see Figure 3a
). The axillary sling eliminates the neck-ring reaction when pad
loads are applied.
The axillary sling force was calculated to minimize the reaction force at T1
for each simulated case of thoracic and/
or lumbar pad placement. The effect
was represented by equal forces along
the medial-lateral line of action at T5
and T6 levels. The updated coordinates
of the centroids of each vertebra (TiL5) due to application of pad loads
were obtained from the finite element
analysis.
The interaction of an orthosis with
the scoliotic curve was simulated using
a two-stage approach that simulated
the procedure used in fitting a patient
with an orthosis. In the first stage, the
deformed shape of the spine was obtained under the application of external loads to simulate curve correction
in the orthosis. These loads consisted of
the transverse forces exerted by the
thoracic and lumbar pads in the case of
a TLSO (see Figure 4a
).
The second stage of the simulation
represented the continuous lateral sup.
port (or transverse load) provided by
the pads to the corrected curve. Having
arrived at the corrected geometry of
the spine in the orthosis, kinematic constraints were introduced at the levels of
pad placements and axillary sling location (in the case of the CTLSO). A linear spring was used between the vertebral centroid and the constraint boundary to simulate the stiffness of the orthosis wall-rib interface at that level
(see Figure 3b
and Figure 4b
).
The model spine then was loaded in
axial compression to simulate the
weight of the body segments above
sacrum. The axial load was distributed
over vertebral centroids T1-L5 using
the mass distribution function (19). The
stability of a scoliotic curve was expressed in terms of its critical load, defined as the value of the maximum axial load the spine can support without
undergoing a permanent increase in its
curvature. This concept is described in
previous studies (11,12,18).
The stability of the primary thoracic
and primary lumbar curve patterns (see
Table A
) was evaluated as a function of
location of the trimline of a TLSO relative to the superior endpoint of the
curve and placement of the thoracic
and lumbar pads relative to the corresponding apices of the curve components. These results were compared to
those obtained with the CTLSO model
for the same curve patterns.
ResultsStabilizing Effect of the CTLSO:
Primary Thoracic Curves
In using the CTLSO for the primary
thoracic curve, maximum stability can
be achieved by placing the thoracic pad
alone at the apex of the primary thoracic
curve (see Figure 5
). Incorrect placement of the thoracic pad inferior to the
apex reduces the stability of the thoracic
curve. Placement of the thoracic pad two
levels inferior to the apex reduces the
stability achieved with the correctly
placed thoracic pad by 16 percent.
A lumbar pad at the apex of the
compensatory lumbar curve tends to
decrease the stability of the primary
thoracic curve that is achieved with a
correctly placed thoracic pad alone. A
lumbar pad one level too superior causes a loss of 13 percent of the stability
gained by a correctly placed thoracic
pad alone.
Stabilizing Effect of the CTLSO:
Primary Lumbar Curves
Maximum stability of the primary lumbar curve can be achieved by placing a
lumbar pad at the apex of the primary
curve with an apical thoracic counterforce of a magnitude great enough to
minimize the neck-ring reaction (see
Figure 6
). A lumbar pad alone at the
apex of the primary lumbar curve without a thoracic counterforce results in a
25 percent smaller critical load value
than that achieved when a thoracic
counterforce is used. The lumbar pad
alone is not as effective in stabilizing
the primary curve because as the spine
is loaded axially (the normal result of
being upright), the curve tends to shift
away from the lumbar pad, thus reducing its stabilizing effect. A thoracic
counterforce acts to maintain contact
between the lumbar pad and the primary curve, thereby improving its stability. Incorrect placement of the lumbar pad one level too superior reduces
the stability by 12 percent.
Stabilizing Effect of a TLSO:
Primary Thoracic Curves
In primary thoracic curves, maximum
stability and curve correction using a
TLSO are achieved with the axillary
trimline at T5-6 and a pad at the apex
of the thoracic curve (see Figure 7
). As
the trimline of the TLSO moves inferior relative to the superior endpoint of
the curve, curve correction decreases,
and a loss of stability of nearly 20 percent results with each level.
Moving the thoracic pad one level
superior to the apex decreases the
curve correction and causes a loss in
stability by 13 percent (see Figure 8
).
Placement of the thoracic pad up to
two levels inferior to the apex has no
appreciable effect on curve correction
and stability. Adding a lumbar pad at
the apex of the compensatory curve decreases the effectiveness of a correctly
placed thoracic pad since the critical
load value decreases by nearly 15 percent. A lumbar pad one level too superior further decreases the correction of
the primary curve and causes a 20 percent decrease in stability as compared
to that achieved by a correctly placed
thoracic pad alone. This is consistent
with the behavior of the lumbar pad
noted for the CTLSO treatment of primary thoracic curves.
Stabilizing Effect of a TLSO:
Primary Lumbar Curves
In primary lumbar curves, optimum stability with a TLSO is achieved with the
trimline located one level inferior to
the apex of the compensatory thoracic
component and a pad load at the apex
of the primary curve (see Figure 9
).
Moving the trimline inferior toward the
superior endpoint of the primary lumbar curve results in a significant loss in
stability. For example, as the trimline location is moved from T9-10 to T11-12,
the critical load decreases by approximately 45 percent.
However, little additional gain in stability of the primary lumbar curve is
achieved by placing the trimline at the
superior endpoint of the compensatory
thoracic component. For example, the
critical load of the primary lumbar
curve supported by the trimline at T5-6
with thoracic and lumbar pads at corresponding apices is only 8 percent
greater than that achieved by placing
the trimline at T9-10 and pad load at
the apex of the lumbar curve.
Incorrect placement of the lumbar
pad has a detrimental effect on the stability of the primary lumbar curve. A
lumbar pad load applied one level superior to the apex decreases the stability achieved by a correctly placed pad
by nearly 10 percent.
Comparison of Optimum Results
In primary thoracic curves, maximum
stability with the CTLSO is achieved
with the maximal pad load and continued lateral support at the apex of the
thoracic curve in conjunction with an
axillary sling force to minimize the
neck-ring reaction. Maximum stability
using a TLSO in these curves is obtained by placing the trimline at the superior endpoint of the curve with a pad
at the apex of the thoracic curve. A
comparison of optimum results of the
two orthoses shows that in primary thoracic curves the optimum stability
achieved with a TLSO is 25 percent less
than that obtained with the CTLSO
(see Figure 10
).
In primary lumbar curves, the best
result with a TLSO is achieved with the
axillary trimline one level inferior to
the apex of the compensatory thoracic
component and maximal pad load and
continued lateral support at the apex of
the lumbar curve. In using the CTLSO
to stabilize primary lumbar curves, optimum stability is obtained with maximal pad support at the apex of the
lumbar curve with an apical thoracic
counterforce (pad load) great enough
to minimize the neck ring reaction. A
comparison of these two orthotic treatment modalities shows nearly equal
critical load values for the primary
lumbar curve (see Figure 10
).
Discussion
The critical load is the smallest value of
axial load at which the maximum bending moment in the spinal curve reaches
the elastic limit in bending and causes
inelastic failure (12,18). Thus, the critical load is a measure of the capacity of
the scoliotic spine to carry an axial load
without causing a permanent increase
in its curvature.
In a previous study (12), the authors
used the critical load of scoliotic curve
as a measure of its stability to understand the clinically observed relationship between curve magnitude and progression; at any age of maturity a larger
curve is much more likely to progress
than a smaller curve. Subsequently, the
critical load measure was used to investigate the problem of progression in
untreated curves of adolescents with
idiopathic scoliosis as a function of
curve pattern (18). The variations in the
incidence of progression of different
curve patterns as noted in the clinical
studies were accurately mirrored in the
findings of the biomechanical model of
curve progression. Thus, thinking about
differences in the stability of a scoliotic
curve as measured by its critical load is
a way of understanding the clinically
observed behavior of scoliotic curves
under a variety of clinical situations.
In this work, the authors have used
the critical load of a scoliotic curve as
measure of its stability for different
boundary conditions that simulate different orthotic design parameters.
Clearly, the absolute values of critical
loads will depend on the assumed value
of the elastic limit in bending and on
other simplifying assumptions used in
the model to approximate the complex
structure. However, because of the
comparative evaluation of the two orthotic treatment modalities, these assumptions do not affect the results.
In the present study, the authors used
a finite element model of the spineorthosis system to simulate the interaction of the spinal orthosis with the spine
in the frontal plane. It is recognized the
spinal curvature in the sagittal plane
and the rotation about the longitudinal
axis of the involved vertebral bodies
are important considerations in the
morphology of idiopathic scoliosis. Further, the analysis was based on estimates of the mechanical properties of
the spine and considered no active neuromuscular involvement. However, the
results of this analysis provide a biomechanical rationale for clinical observations regarding the outcome of orthotic
treatment for scoliosis.
The results indicate that in primary
thoracic curves, maximum stability with
the CTLSO is achieved with the maximal pad load and continued lateral support at the apex of the thoracic curve in
conjunction with an axillary sling force
to minimize the neck ring reaction.
Maximum stability using a TLSO in
these curves is obtained by placing the
trimline at the superior endpoint of the
curve with a pad at the apex of the thoracic curve. These results do not undermine the need for a lumbar pad to reduce a lumbar compensatory curve;
however, they may help explain why
single thoracic curves, treated with only
a thoracic pad, reduce more than thoracic curves in the presence of a lumbar
component where both thoracic and
lumbar pads are used.
In using the CTLSO to stabilize primary lumbar curves, optimum stability
is obtained with maximal pad support
at the apex of the lumbar curve with an
apical thoracic counterforce great
enough to minimize the neck ring reaction. In primary lumbar curves, the optimum result with a TLSO is achieved
with the trimline one level inferior to
the apex of the compensatory thoracic
component and maximal pad load and
continued lateral support at the apex of
the lumbar curve.
Comparisons show a properly fitted
TLSO to be as effective as the CTLSO
in stabilizing the primary lumbar
curves. On the other hand, in primary
thoracic curves the optimum stability
achieved with a TLSO is approximately 25 percent less than that obtained
with the CTLSO. This helps explain
why many, but not all, thoracic curves
are well-controlled with a TLSO. For
patients in whom a TLSO is not able to
control a primary thoracic curve, a
CTLSO may provide enough additional support to stabilize the curve.
However, as the results show, correct
placement of the pads is important. Optimum results with an orthosis can be
achieved when the pad loads are applied at the apical level of the curve. Incorrect placement of the pads reduces
the stabilizing effect. This effect is
greater in the lumbar area as a mistake
of even one level too superior reduces
the benefit of both the thoracic and
lumbar pads. The detrimental effect of
incorrect pad placement on the stability of the curve observed in the present
study is consistent with the observations of Andriacchi et al. (15) who noted that correction of the thoracic curve
decreased when the pad was placed
two levels inferior to the apex of the
curve. Therefore, careful attention must
be given to pad placement.
Incorrect pad placement can occur as
a result of at least two fabrication and
fitting mistakes. First, it is quite possible
the lumbar pad is simply positioned too
high. The apex of the lumbar curves is
just above the iliac crest, and it is easy
to place the pad too superior.
The second mistake is much more
common. The waist diameter can be
fabricated and fitted too small, causing
the entire orthosis to move superior.
When this occurs, the correctly placed
pads are functionally one or more levels too superior, and the effect of the
pads is diminished. In addition, if the
patient has grown since the last visit
and the previously well-fitted pelvic
girdle has migrated superiorly, the
curve correction also is diminished.
Thus, the results of the biomechanical
model underscore the need for meticulous fit in the waist and pelvis and the
importance of proper pad placement
and routine follow-up adjustments for
growth.
Conclusion
Clinical considerations of cosmesis and
geographical regionalization of orthoses are helpful in determining which
orthosis may be more tolerable for a
particular patient. Other clinical factors
in selecting an appropriate orthosis are
1) selecting the orthosis with which a
clinical team in a given region has the
most experience and 2) selecting the orthosis that has provided the best outcomes. Factors such as curve stability,
age, growth rate and progression risk
factor should be primary considerations
when selecting the appropriate orthosis.
For thoracic primary curves, a well-fitted CTLSO provides more stability
but may not be necessary for an older
patient with a 25-degree curve that already has a high initial critical load value due to its small magnitude and low
risk of progression because the patient
is near maturity. A CTLSO may be
more appropriate for an 11-year-old
patient with a 45-degree curve since the
critical load value is small due to the
curve's large magnitude; such a patient's upcoming peak height velocity
growth puts him or her in the highest
progression risk group for adolescent
idiopathic scoliosis. For a 25- or 45-degree lumbar primary curve, a TLSO
will be adequate, regardless of age
growth or stability, since the CTLSO
does not provide greater stability (critical load) than the TLSO.
The most appropriate orthosis is one
that will provide a balance of the best
outcome, the most comfort and the
greatest amount of cosmesis.
Acknowledgments
This study was supported in part by funds
from the Rehabilitation Research and Development Center, Hines VA Hospital,
Hines, Ill. The authors thank Patrick Carrico for his help in preparing the illustrations.
AVINASH C. PATWARDHAN, PhD,
works in the department of orthopedic surgery at Loyola University, 2160 S First Ave.,
Maywood, IL 60153, (708) 343-7200, ext.
5804, and also works at the Rehabilitation
Research and Development Center at the
VA Hospital in Hines, Ill.
THOMAS M. GAVIN, CO, is president
and director of clinical services for BioConcepts Inc. in Burr Ridge, Ill., as well as a
teaching associate at Loyola University
Medical Center and a research orthotist at
the VA Hospital in Hines, Ill.
WILTON H. BUNCH, MD, PHD, is a student at the Church Divinity School of the Pacific in Berkeley, Calif.
VICTORIA M. DVONCH, MD, works in
the department of human restoration at
Stanford University in Palo Alto, Calif.
RAY VANDERBY JR., PhD, works in
the division of orthopaedic surgery at the
University of Wisconsin in Madison, Wis.
KEVIN P MEADE, PhD, works in the
Rehabilitation Research and Development
Center at the VA Hospital in Hines, Ill., and
in the department of mechanical, materials
and aerospace engineering at the Illinois institute of Technology in Chicago.
MARK SARTORI works in the department of orthopaedic surgery at Loyola University in Maywood, Ill., and at the Rehabilitation Research and Development Center at
the VA Hospital in Hines, Ill.
References:
- Gavin TM, Shurr DG, Patwardhan AG.
Orthotic treatment for spinal disorders. In:
SL Weinstein, ed. The pediatric spine.
Raven Press, 1993: 1795-828.
- Blount WP, Moe JH. The Milwaukee
brace. Baltimore: Williams and Wilkins Co.,
1973.
- Carr WA, Moe JH, Winter RB, Lonstein J. Treatment of idiopathic scoliosis in
the Milwaukee brace: long-term results.
JBJS 1980;62A:599-612.
- Edmonsson A, Morris J. Follow-up
study of Milwaukee brace treatment in patients with idiopathic scoliosis. Clin Orthop
1977;126:58-61.
- Lonstein JE, Winter RL. Milwaukee
brace treatment of adolescent idiopathic
scoliosis-review of 1,020 patients. JBJS (in
press).
- Nachemson A, Peterson LE. Scoliosis
Research Society brace study report: effectiveness of brace treatment in moderate
adolescent idiopathic scoliosis-actors predicting progress in moderate adolescent idiopathic scoliosis. Proceedings of the 28th
annual meeting of the Scoliosis Research
Society, Dublin, Ireland, September 1993.
- Bunnell WP, MacEwen GD, Jayakumar S. The use of plastic jackets in the nonoperative treatment of idiopathic scoliosis.
JBJS 1980;62A:31-8.
- Gavin TM, Bunch WH, Dvonch VM.
The Rosenberger scoliosis orthosis. J Assn
Children's Pros-Orth Clin 1986;21:35-8.
- Jodoin A, Hall JE, Watts HG, Miller
ME, Michelli U, Riseborough EJ. Treatment of idiopathic scoliosis by the Boston
brace system. Early results. Orthop Trans
1981;5:22.
- McCollough NC, Schultz M, Javeck
N, Latta L. Miami TLSO in the management of scoliosis: preliminary results in 100
cases. J Ped Orthop 1981;1:141-52.
- Bunch WH, Patwardhan AG, Dvonch
VM. A mechanism of action of spinal orthoses. Inter-Clinic Info Bull 1983;18:5:7-10.
- Patwardhan AG, Bunch WH, Meade
KP, Vanderby R, Knight GW. A biomechanical analog of curve progression and
orthotic stabilization in idiopathic scoliosis.
J Biomech 1986;19:2:103-17.
- Lindbeck L. Analysis of functional
scoliosis by means of an anisotropic beam
model of the human spine. J Biomech Eng
1985; 107:281-5.
- Mulcahy T, Galante J, DeWald RL,
Schultz AB, Hunter JC. A follow-up study
of forces acting in the Milwaukee brace on
patients undergoing treatment for idiopathic scoliosis. Clin Orthop 1973;93:53-68.
- Andriacchi TP, Schultz AB, Belytschko TB, DeWald RL. Milwaukee brace
correction of idiopathic scoliosis. JBJS
1976;58-A:806-15.
- Moe JH, Winter RB, Bradford DS,
Lonstein JE. Scoliosis and other spinal deformities. Philadelphia: WB. Saunders Co.,
1978.
- Vanderby R, Daniele MW, Patwardhan AG, Bunch, WH. A method for identification of in vivo segmental stiffness properties of the spine. J Biomech Eng
1986;108:312-6.
- Meade KP, Bunch WH, Vanderby R,
Patwardhan AG, Knight GW Progression
of unsupported curves in adolescent idiopathic scoliosis. Spine 1987;12:6:520-6.
- Cramer HJ, Liu YK, von Rosenberg
D. A distributed parameter model of the inertially loaded human spine. J Biomech
1976;9:115-30.
- Agostoni B, Mognoni G,Torri G, Miserocchi G. Forces deforming the rib cage.
Respiration Phys 1966;2:105-17.
- Andriacchi TP, Schultz AB, Belytschko TB, Galante JO: A model for studies of mechanical interactions between the
human spine and rib cage. J Biomech
1974;7:497-507.
|
|
