0
Research Papers

A Low-Dimensional Sagittal-Plane Forward-Dynamic Model for Asymmetric Gait and Its Application to Study the Gait of Transtibial Prosthesis Users

[+] Author and Article Information
S. Srinivasan

Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600036, Indiasujsree@iitm.ac.in

E. R. Westervelt

 GE Global Research, Niskayuna, NY 12309eric.westervelt@ge.com

A. H. Hansen

 Jesse Brown VA Medical Center, Chicago, IL 60411; Department of Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University Chicago, IL 60611a-hansen@northwestern.edu.

A holonomic constraint is a constraint that depends only on the coordinates of the system and not on the rate of change of the coordinates.

Perry (20) described the action over a step of the ankle-foot complex using three rockers based on the center of rotation of the shank with respect to the foot. The ROS is a model that uses the COP to generate a single rocker to describe the action of the ankle-foot complex.

J Biomech Eng 131(3), 031003 (Jan 05, 2009) (9 pages) doi:10.1115/1.3002757 History: Received June 27, 2007; Revised June 07, 2008; Published January 05, 2009

This paper presents an extension of a recently developed low-dimensional modeling approach for normal human gait to the modeling of asymmetric gait. The asymmetric model is applied to analyze the gait dynamics of a transtibial prosthesis user, specifically the changes in joint torque and joint power costs that occur with variations in sagittal-plane alignment of the prosthesis, mass distribution of the prosthesis, and roll-over shape of the prosthetic foot being used. The model predicts an increase in cost with addition of mass and a more distal location of the mass, as well as the existence of an alignment at which the costs are minimized. The model’s predictions also suggest guidelines for the selection of prosthetic feet and suitable alignments. The results agree with clinical observations and results of other gait studies reported in the literature. The model can be a useful analytical tool for more informed design and selection of prosthetic components, and provides a basis for making the alignment process systematic.

FIGURES IN THIS ARTICLE
<>
Copyright © 2009 by American Society of Mechanical Engineers
Your Session has timed out. Please sign back in to continue.

References

Figures

Grahic Jump Location
Figure 7

The minima paths of the total joint torque (a) and joint power (b) costs for variation in mass distribution and AP alignment. The mass location is the distance between the knee and the location of the added mass expressed as a percentage of the shank length. Depending on the mass and mass distribution, the lowest costs occur at the +40mm or +50mm AP shifts.

Grahic Jump Location
Figure 8

The total joint torque (a) and joint power (b) costs for one gait cycle with different radii and variation in AP alignment of the prosthetic side ROS. The different radii are expressed as a percentage of LL. AP shift of zero and radius of 36% LL correspond to sound leg ROS. For the larger radii, a step cannot be completed for the more anterior alignments.

Grahic Jump Location
Figure 9

Steady-state walking speed with different radii of the prosthetic side ROS and different alignments. The different radii are expressed as a percentage of LL. For the larger radii, a step cannot be completed for the more anterior alignments.

Grahic Jump Location
Figure 10

Comparison of the step length of the prosthetic (dotted lines) or the sound leg (solid lines) with different radii of the prosthetic side ROS and different alignments. The different radii are expressed as a percentage of LL. For the larger radii, a step cannot be completed for the more anterior alignments.

Grahic Jump Location
Figure 11

ROSs of different radii placed at the nominal alignment (a) and at optimal alignment (b) on the prosthetic side. The different radii are expressed as a percentage of leg length. The nominal alignment corresponds to the location of the sound side ROS. At optimal alignment, the ROS of different radii appear to nest toward a common shape.

Grahic Jump Location
Figure 1

Illustration of the parsimony of human gait over a normal gait cycle. Average joint angles as a percentage of gait cycle for five adult subjects with normal gait using five trials each (bold). The dashed lines are the pointwise 1 standard deviation minimum and maximum joint angles. The normal gait cycle is composed of two symmetric steps, each comprised of a SS and a DS phase. Toe-off (TO) signals transition from DS to SS while HC signals transition from SS to DS. The subscripts “L” and “R” indicate the left and right legs as the stance leg. The superscripts “+” and “−” indicate the beginning and end of each phase. (Data courtesy of J. Linskell, Limb Fitting Centre, Dundee, Scotland (21).)

Grahic Jump Location
Figure 2

Coordinates for the minimal anthropomorphic model in SS and DS. Note the choice of coordinates as one absolute qa and the others relative. The relative coordinates specify the posture of the model, and the circles indicate the internal DOF. Note also the additional DOF at the trailing ankle in the DS model. The stance ankle-foot complex is modeled using the ROS (19). The ROS does not apply to the swing foot.

Grahic Jump Location
Figure 3

The ROS is obtained by representing the center of pressure over a step in a shank-based coordinate system with the ankle as origin (19). The ROS is a model for the effective rocker the ankle-foot complex (physiologic or prosthetic) conforms to in the period between heel contact and opposite heel contact. In the physiologic case, the shape is well approximated by a circular arc and allows the stance foot motion to be modeled as rolling contact with the ground.

Grahic Jump Location
Figure 4

The total joint torque (a) and joint power (b) costs for one gait cycle with varying alignments. A positive value of the AP shift indicates that the foot is moved anterior to the nominal. The ROS radius used for the prosthetic side is the biomimetic radius.

Grahic Jump Location
Figure 5

The joint torque costs for the hip (dashed) and knee (solid) of the prosthetic leg in swing, normalized by walking speed. The costs increase with increased mass and more distal location of the added mass.

Grahic Jump Location
Figure 6

The total joint torque (a) and joint power (b) costs for different AP alignments (−20mmto+60mm) of the prosthetic side ROS when the mass distribution is varied. The mass location is the distance between the knee and the location of the added mass expressed as a percentage of the shank length. In the obscured portions of (a), the ordering of the surfaces is preserved. In (b), the ordering of the surfaces is not preserved near the optimal alignment zone indicating that mass reduction may sometimes result in increased total joint power costs.

Tables

Errata

Discussions

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In