A Proposed New ObstacleSet Algorithm for Modeling Deltoid

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A Proposed New Obstacle-Set Algorithm for
Modeling Deltoid
Tiffany Xu Mentor Dr. Brian Garner
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Presentation Outline

• I, Introduction to muscle modeling and why
  that is needed?
• II, Application areas of muscle modeling.
• III, Introduction to four mostly used muscle
  modeling methods.
• IV, Studies carried out using the obstacle-set
  model.
• Description of muscle modeling using obstacle-set
  model.
• Difficulties encountered in modeling deltoid.
• V, A new obstacle-set model.
• Algorithm/methods.
• Results/comparison with data from other studies.
  
• Advantage of the new obstacle-set model.
• VI, Conclusion.
• VII, Questions.

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Introduction to Muscle Modeling

• In order to understand how each muscle works to
  influence our body behavior, all the following
  factors need to be studied
• Point of force application
• Direction of force application
• Force magnitude
• But, not all of those factors could be obtained
  directly, which is why computer simulation of
  muscle activity emerges as a popular method to
  approximate the muscle moment arm.

Through out the study of muscle mechanics, muscle
moment arm is an eternal topic. Proper
representation of muscle paths in musculoskeletal
models is important for accurately modeling the
magnitude and line-of-action of muscle forces.
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Applications of Muscle Modeling

• Biomechanics (North Carolina State University,
  ergonomics research)
• Computer graphics
• 1 Patria A. Hume, Justin Keogh and Duncan Reid,
  The Role of Biomechanics in Maximizing Distance
  and Accuracy of Golf Shots. Sports Med
  2005,35(5) 429-449.
• 2 Arpad Illyes, Rita M. Kiss, Shoulder Muscle
  Activity During Pushing, Pulling, Elevation and
  Overhead Throw. Journal of Electromyography and
  Kinesiology 15(2005) 282-289.
• 3 Marcus G. Pandy, Computer Modeling and
  Simulation of Human Movement. Annual Reviews of
  Biomedical Engineering, 2001. 3245-73.

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Straight-line model
Four Mostly Used Muscle Wrapping Methods
Centroid line model
3D model via finite element algorithm
Obstacle-set model
Difficulty of Simulating the Muscle Path Tension
between desire to have model accuracy, and desire
to have simplicity and computational efficiency.
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Obstacle-set Model

• The muscle path in this method is formed by
  several segments of straight lines and curved
  lines joined together by via points. And the
  anatomical constrains are modeled by cylinder,
  sphere, stub, or other combination of those
  geometries.

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Obstacle-set Model Has A Limitation in Modeling
Broad Muscle

• However, modeling some broad muscles crossing
  joints with wide ranges of motion can be
  difficult owing to
• Broad muscles are modeled with multiple bands.
• Each bands path is computed independently.
• The independent bands of the deltoid have a
  tendency to slip around to unrealistic positions
  behind the sphere.

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New Obstacle-set Algorithm --improvement was made
The aim of this study was to develop a new
obstacle-set algorithm that accounts for
connectivity between muscle fibers, that will
keep the fibers staying on the surface of the
obstacle-set without any slip.
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New Obstacle-set Algorithm for Modeling Deltoid

• Origin sites on a fixed clavicle/scapula bone,
  and insertion sites on a moving humerus, were
  defined.
• A sphere obstacle was defined to represent
  anatomy underneath the deltoid.
• Reference planes were specified.
• Fixed angles between the path and reference
  planes were chosen to reflect the breadth of the
  deltoid muscle between bands.
• Minimum-distance path of each muscle band around
  the sphere and within a path plane was
  calculated.

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New Obstacle-set Algorithm for Modeling Deltoid
The muscle paths were then applied onto the bone
structure reconstructed from the Visible Human
Project data.
Anterior, medial, and posterior muscle path
planes and their orientation reference planes
and their orientations.
Sphere as the obstacle
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Process of Simulation
60o
0o
30o

• Move/rotate the humerus
• Orientation of the anterior muscle path plane
  determined
• Orientation of the medial and posterior muscle
  path planes changed
• Minimum length of each muscle path computed
• Above steps repeated to find the orientation
  value of the anterior muscle path plane which
  minimized the sum of the path lengths

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Results of the New Obstacle-set Model

• No slip.
• Computational time was less than a millisecond.
• Wide range of shoulder joint motion.
• Realistic configurations of the hypothetical
  deltoid.

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Results of the New Obstacle-set Model
Why Say It Is Realistic?
Abduction moment arm for anterior, medial and
posterior deltoid from this new obstacle-set
model, compared with experimental data from other
two studies.
-- Obstacle-set -- Liu -- Otis
1/3, Moment arm of anterior deltoid during
abduction
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Results of the New Obstacle-set Model
-- Obstacle-set -- Liu -- Otis
-- Obstacle-set -- Liu -- Otis
2/3, Moment arm of medial deltoid during abduction
3/3, Moment arm of posterior deltoid during
abduction
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Advantage of the New Obstacle-set Algorithm

• Advantages of this algorithm include
• simplicity
• realism
• computational efficiency
• connectivity between muscle fibers taken into
  account
• flexible algorithm, so that an arbitrarily large
  number of muscle bands could be used to model
  broad muscles.

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Conclusion
Compared to other modeling methods, the new
obstacle-set algorithm, is not only simple and
fast, but also flexible and realistic. This
improved obstacle-set model, handles the problem
of slip that happened in the original one. The
derived connectivity algorithm keeps the fibers
of a broad muscle staying on surface of the
sphere-shaped obstacle, which makes the new
obstacle-set model robust. Comparison to the
experimental data reveals a good approximation of
the moment arm. But more experimental data needs
to be studied and compared with, so that the
realisticness of this new model could be
improved.
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Thank you! Any Questions?
References 1 Garner B.A., Pandy M.G., The
Obstacle-Set Method for Representing Muscle Paths
in Musculoskeletal Models. Computer Methods in
Biomechanics and Biomedical Engineering, Vol. 3,
pp. 1-30. 2 Silva S. Blemker and Scott L. Delp,
Three-Dimensional Representation of Complex
Muscle Architectures and Geometries. Annals of
Biomedical Engineering, Vol. 33, No. 5, May 2005
pp.661-673. 3 Garner, B. A. and Pandy, M.G., A
kinematic model of the upper limb based on the
visible Human Project dataset. Computer Methods
in Biomechanics and Biomedical Engineering. 4
Brian A. Garner and Marcus G. Pandy,
Musculoskeletal Model of the Upper Limb Based on
the Visible Human Male Dataset. Computer Methods
in Biomechanics and Biomedical Engineering, Vol.
4, pp.93-126. 5 JC Otis, CC Jiang, TL
Wickiewicz, MG Peterson, RF Warren and TJ
Santner,Changes in the moment arms of the rotator
cuff and deltoid muscles with abduction and
rotation. Department of Biomechanics, Hospital
for Special Surgery, New York, N.Y. 10021.