Musculoskeletal modeling and simulation techniques have been used to gain insights into movement disabilities for many populations, such as ambulatory children with cerebral palsy (CP). The individuals who can benefit from these techniques are often limited to those who can walk without assistive devices, due to challenges in accurately modeling these devices. Specifically, many children with CP require the use of ankle-foot orthoses (AFOs) to improve their walking ability, and modeling these devices is important to understand their role in walking mechanics. The purpose of this study was to quantify the effects of AFO mechanical property assumptions, including rotational stiffness, damping, and equilibrium angle of the ankle and subtalar joints, on the estimation of lower-limb muscle forces during stance for children with CP. We analyzed two walking gait cycles for two children with CP while they were wearing their own prescribed AFOs. We generated 1000-trial Monte Carlo simulations for each of the walking gait cycles, resulting in a total of 4000 walking simulations. We found that AFO mechanical property assumptions influenced the force estimates for all the muscles in the model, with the ankle muscles having the largest resulting variability. Muscle forces were most sensitive to assumptions of AFO ankle and subtalar stiffness, which should therefore be measured when possible. Muscle force estimates were less sensitive to estimates of damping and equilibrium angle. When stiffness measurements are not available, limitations on the accuracy of muscle force estimates for all the muscles in the model, especially the ankle muscles, should be acknowledged.

References

References
1.
Zajac
,
F. E.
,
Neptune
,
R. R.
, and
Kautz
,
S. A.
,
2003
, “
Biomechanics and Muscle Coordination of Human Walking—Part II: Lessons From Dynamical Simulations and Clinical Implications
,”
Gait Posture
,
17
(
1
), pp.
1
17
.
2.
Pandy
,
M. G.
,
Lin
,
Y.-C.
, and
Kim
,
H. J.
,
2010
, “
Muscle Coordination of Mediolateral Balance in Normal Walking
,”
J. Biomech.
,
43
(
11
), pp.
2055
2064
.
3.
Silverman
,
A. K.
, and
Neptune
,
R. R.
,
2012
, “
Muscle and Prosthesis Contributions to Amputee Walking Mechanics: A Modeling Study
,”
J. Biomech.
,
45
(
13
), pp.
2271
2278
.
4.
Knarr
,
B. A.
,
Reisman
,
D. S.
,
Binder-Macleod
,
S. A.
, and
Higginson
,
J. S.
,
2014
, “
Changes in Predicted Muscle Coordination With Subject-Specific Muscle Parameters for Individuals After Stroke
,”
Stroke Res. Treat.
,
2014
, pp.
1
7
.
5.
Peterson
,
C. L.
,
Hall
,
A. L.
,
Kautz
,
S. A.
, and
Neptune
,
R. R.
,
2010
, “
Pre-Swing Deficits in Forward Propulsion, Swing Initiation and Power Generation by Individual Muscles During Hemiparetic Walking
,”
J. Biomech.
,
43
(
12
), pp.
2348
2355
.
6.
Chambers
,
H. G.
,
2001
, “
Treatment of Functional Limitations at the Knee in Ambulatory Children With Cerebral Palsy
,”
Eur. J. Neurol.
,
8
(
5
), pp.
59
74
.
7.
Steele
,
K. M.
,
Van der Krogt
,
M. M.
,
Schwartz
,
M. H.
, and
Delp
,
S. L.
,
2012
, “
How Much Muscle Strength Is Required to Walk in a Crouch Gait?
,”
J. Biomech.
,
45
(
15
), pp.
2564
2569
.
8.
Knutson
,
L. M.
, and
Clark
,
D. E.
,
1991
, “
Orthotic Devices for Ambulation in Children With Cerebral Palsy and Myelomeningocele
,”
Phys. Ther.
,
71
(
12
), pp.
947
960
.
9.
Sumiya
,
T.
,
Suzuki
,
Y.
, and
Kasahara
,
T.
,
1996
, “
Stiffness Control in Posterior-Type Plastic Ankle-Foot Orthoses: Effect of Ankle Trimline—Part 2: Orthosis Characteristics and Orthosis/Patient Matching
,”
Prosthet. Orthotics Int.
,
20
(
2
), pp.
132
137
.http://www.oandplibrary.org/poi/1996_02_132.asp
10.
Yamamoto
,
S.
,
Ebina
,
M.
,
Iwasaki
,
M.
,
Kubo
,
S.
,
Kawai
,
H.
, and
Kayashi
,
T.
,
1993
, “
Comparative Study of Mechanical Characteristics of Plastic AFOs
,”
J. Prosthet. Orthotics
,
5
(
2
), pp.
59
70
.http://www.oandp.org/jpo/library/1993_02_059.asp
11.
Yamamoto
,
S.
,
Miyazaki
,
S.
, and
Kubota
,
T.
,
1993
, “
Quantification of the Effect of the Mechanical Property of Ankle-Foot Orthoses on Hemiplegic Gait
,”
Gait Posture
,
1
(
1
), pp.
27
34
.
12.
Bregman
,
D. J. J.
,
Rozumalski
,
A.
,
Koops
,
D.
,
de Groot
,
V.
,
Schwartz
,
M. H.
, and
Harlaar
,
J.
,
2009
, “
A New Method for Evaluating Ankle Foot Orthosis Characteristics: BRUCE
,”
Gait Posture
,
30
(
2
), pp.
144
149
.
13.
Kobayashi
,
T.
,
Leung
,
A. K. L.
, and
Hutchins
,
S. W.
,
2011
, “
Techniques to Measure Rigidity of Ankle-Foot Orthosis: A Review
,”
J. Rehabil. Res. Dev.
,
48
(
5
), pp.
565
576
.
14.
Schwartz
,
M. H.
,
Rozumalski
,
A.
,
Truong
,
W.
, and
Novacheck
,
T. F.
,
2013
, “
Predicting the Outcome of Intramuscular Psoas Lengthening in Children With Cerebral Palsy Using Preoperative Gait Data and the Random Forest Algorithm
,”
Gait Posture
,
37
(
4
), pp.
473
479
.
15.
Dreher
,
T.
,
Vegvári
,
D.
,
Wolf
,
S. L.
,
Klotz
,
M.
,
Müller
,
S.
,
Metaxiotis
,
D.
,
Wenz
,
W.
,
Döderlein
,
L.
, and
Braatz
,
F.
,
2013
, “
Long-Term Effects After Conversion of Biarticular to Monoarticular Muscles Compared With Musculotendinous Lengthening in Children With Spastic Diplegia
,”
Gait Posture
,
37
(
3
), pp.
430
435
.
16.
Delp
,
S. L.
,
Loan
,
P. J.
,
Hoy
,
M. G.
,
Zajac
,
F. E.
,
Topp
,
E. L.
, and
Rosen
,
J. M.
,
1990
, “
An Interactive Graphics-Based Model of the Lower Extremity to Study Orthopaedic Surgical Procedures
,”
IEEE Trans. Biomed. Eng.
,
37
(
8
), pp.
757
767
.
17.
Yamaguchi
,
G. T.
, and
Zajac
,
F. E.
,
1989
, “
A Planar Model of the Knee Joint to Characterize the Knee Externsor Mechanism
,”
J. Biomech.
,
22
(
1
), pp.
1
10
.
18.
Anderson
,
F. C.
, and
Pandy
,
M. G.
,
1999
, “
A Dynamic Optimization Solution for Vertical Jumping in Three Dimensions
,”
Comput. Methods Biomech. Biomed. Eng.
,
2
(
3
), pp.
201
231
.
19.
Anderson
,
F. C.
, and
Pandy
,
M. G.
,
2001
, “
Dynamic Optimization of Human Walking
,”
ASME J. Biomech. Eng.
,
123
(
5
), pp.
381
390
.
20.
Lu
,
T.-W.
, and
O'Connor
,
J. J.
,
1999
, “
Bone Position Estimation From Skin Marker Co-Ordinates Using Global Optimisation With Joint Constraints
,”
J. Biomech.
,
32
(
2
), pp.
129
134
.
21.
Thelen
,
D. G.
, and
Anderson
,
F. C.
,
2006
, “
Using Computed Muscle Control to Generate Forward Dynamic Simulations of Human Walking From Experimental Data
,”
J. Biomech.
,
39
(
6
), pp.
1107
1115
.
22.
Bregman
,
D. J. J.
,
De Groot
,
V.
,
Van Diggele
,
P.
,
Meulman
,
H.
,
Houdijk
,
H.
, and
Harlaar
,
J.
,
2010
, “
Polypropylene Ankle Foot Orthoses to Overcome Drop-Foot Gait in Central Neurological Patients: A Mechanical and Functional Evaluation
,”
Prosthet. Orthotics Int.
,
34
(
3
), pp.
293
304
.
23.
Condie
,
D. N.
, and
Meadows
,
C. B.
,
1977
, “
Some Biomechanical Considerations in the Design of Ankle-Foot Orthoses
,”
Orthotics Prosthet.
,
31
(
3
), pp.
45
52
.http://www.oandplibrary.org/op/1977_03_045.asp
24.
Crabtree
,
C. A.
, and
Higginson
,
J. S.
,
2009
, “
Modeling Neuromuscular Effects of Ankle Foot Orthoses (AFOs) in Computer Simulations of Gait
,”
Gait Posture
,
29
(
1
), pp.
65
70
.
25.
Klasson
,
B.
,
Convery
,
P.
, and
Raschke
,
S.
,
1998
, “
Test Apparatus for the Measurement of the Flexibility of Ankle-Foot Orthoses in Planes Other Than the Loaded Plane
,”
Prosthet. Orthotics Int.
,
22
(
1
), pp.
45
53
.http://www.oandplibrary.org/poi/1998_01_045.asp
26.
Major
,
R. E.
,
Hewart
,
P. J.
, and
Macdonald
,
A. M.
,
2004
, “
A New Structural Concept in Moulded Fixed Ankle Foot Orthoses and Comparison of the Bending Stiffness of Four Constructions
,”
Prosthet. Orthotics Int.
,
28
(
1
), pp.
44
48
.http://www.tandfonline.com/doi/abs/10.3109/03093640409167924?journalCode=ipoi20
27.
Sumiya
,
T.
,
Suzuki
,
Y.
, and
Kasahara
,
T.
,
1996
, “
Stiffness Control in Posterior-Type Plastic Ankle-Foot Orthoses: Effect of Ankle Trimline—Part 1: A Device for Measuring Ankle Moment
,”
Prosthet. Orthotics Int.
,
20
(
2
), pp.
129
131
.http://www.oandplibrary.org/poi/1996_02_129.asp
28.
Kobayashi
,
T.
,
Leung
,
A. K. L.
,
Akazawa
,
Y.
,
Naito
,
H.
,
Tanaka
,
M.
, and
Hutchins
,
S. W.
,
2010
, “
Design of an Automated Device to Measure Sagittal Plane Stiffness of an Articulated Ankle-Foot Orthosis
,”
Prosthet. Orthotics Int.
,
34
(
4
), pp.
439
448
.
29.
Easley
,
S. K.
,
Pal
,
S.
,
Tomaszewski
,
P. R.
,
Petrella
,
A. J.
,
Rullkoetter
,
P. J.
, and
Laz
,
P. J.
,
2007
, “
Finite Element-Based Probabilistic Analysis Tool for Orthopaedic Applications
,”
Comput. Methods Programs Biomed.
,
85
(
1
), pp.
32
40
.
30.
Middleton
,
E. A.
,
Hurley
,
G. R. B.
, and
McIlwain
,
J. S.
,
1988
, “
The Role of Rigid and Hinged Polypropylene Ankle-Foot-Orthoses in the Management of Cerebral Palsy: A Case Study
,”
Prosthet. Orthotics Int.
,
12
(
3
), pp.
129
135
.http://www.oandplibrary.org/poi/1988_03_129.asp
31.
Gage
,
J. R.
,
1990
, “
Surgical Treatment of Knee Dysfunction in Cerebral Palsy
,”
Clin. Orthop. Relat. Res.
,
253
, pp.
45
54
.
32.
Kamp
,
F. A.
,
Lennon
,
N.
,
Holmes
,
L.
,
Dallmeijer
,
A. J.
,
Henley
,
J.
, and
Miller
,
F.
,
2014
, “
Energy Cost of Walking in Children With Spastic Cerebral Palsy: Relationship With Age, Body Composition and Mobility Capacity
,”
Gait Posture
,
40
(
1
), pp.
209
214
.
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