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INDIVIDUALIZED MUSCULOSKELETAL MODELING AND IT’S
EFFECT ON THE PARAMETERS OF GAIT
Scheys L., M.Sc.1,2; Jonkers I., Ph.D.2; Spaepen A., M.Sc. Ph.D.2; Suetens P., M.Sc. Ph.D.1
1Katholieke
2 Katholieke
Universiteit Leuven, Medical Image Computing (Radiology-ESAT/PSI), Belgium
Universiteit Leuven, Laboratory of ergonomics and applied biomechanics, Belgium
Abstract
In previous research, gait analysis has already
proven it’s added value. Musculoskeletal modeling
augments this biomechanical analysis of muscle
function during gait. However, the added value of
an individualized musculoskeletal model based on
MR images over a scaled generic model, which is
nowadays commonly used for this application, is
unexplored. The present work compares both
approaches on the calculation of muscle moment
arms.
1
Introduction
Today, most of the software packages for gait
analysis rely on a generic model of the lower
extremity, i.e. the musculoskeletal geometry of an
average-sized adult male [1,4]. For several
applications, this generic model needs to be
accommodated for differences in segment length
and/or aberrant musculoskeletal geometry [2]. This
is usually done by rescaling or deforming a generic
model to approximate the patient’s musculoskeletal
geometry. As a second approach, one can use
medical images (esp. MRI) to build subject-specific
models. Describing the impact of both approaches
on the analysis of function of the major muscle
groups of the lower limb and especially their
moment arms during gait is the scope of this work.
2
Materials and methods
Using a three plane T1 weighted spin echo
sequence, magnetic resonance images were
acquired of the lower extremity from a nonpathologic adult subject (25 year) and a highly
detailed musculoskeletal model was created. Bone
structures were segmented semi-automatically.
Attachment points of 20 major muscle groups of
the lower limb were identified, referenced to
anatomy books [3] and their muscle paths were
defined using a centroid approach. In a second
phase the generic model from the gait simulation
software SIMM [4] was rescaled using bone
dimensions measured on the available medical
images. Finally, for both models the moment arms
of the muscles were analyzed using SIMM.
3
Results
When analyzing the moment arm lengths for the
delineated muscles in the three different planes of
Belgian Day on Biomedical Engineering
joint movement (frontal, sagittal and transversal),
one can observe large differences in the moment
arms as estimated by both models (figure).
Maximum moment arm lengths differ from 0.76%
up to 476.8% with a mean of 36.84%. Minimum
moment arm lengths differ from 0.072% up to
233.1% with a mean of 38.53%. In certain parts of
the gait cycle the adductor magnus inferior and the
adductor brevis even perform opposite muscle
functions in each of the models. The add magnus
superior showed an additional time shift in
achieving minimal and maximal moment arm
lengths during the gait cycle .
4
Discussion
Despite the relative small rescaling factors (1.15)
used, the calculated moment arms differ
substantially. Larger discrepancies are to be
expected in a pediatric population. The
development of a database of pediatric
musculoskeletal models therefore is mandatory.
Acknowledgements
We acknowledge the support from Flanders’ Fund for
Scientific Research (FWO-Vlaanderen) for this project
on: “Personalised musculoskeletal modelling of the
pathological lower extremity using MR images: usability
for biomechanical analysis” (G.0570.05)
References
[1] Bleck EB. Orthopaedic management in cerebral
palsy, 1987, pages 142–212.
[2] Brand RA et al., 1982, Journal of biomechanical
engineering, vol 104, pages 304-310
[3] Cahill D.R., Orland M.J. 1984, Atlas of crosssectional anatomy, Lea & Febiger
[4] MusculoGraphics Inc., Software for Interactive
Musculoskeletal Modeling (SIMM)
October 28, 2005