Motion analysis has been used in gait evaluation, sports performance, and basic research to understand the musculoskeletal movement of the human body. Early models that arose from work in clinical gait analysis are still used today, even though the computation and camera limitations that influenced them are rapidly disappearing. These models can likely be further enhanced by additional work, especially in the area of the foot and ankle. Although several recent studies have shown the usefulness of multi-segment foot models, these have been limited primarily to kinematic analyses. Accurate ankle and foot joint kinetics may provide greater insight into normal and pathological foot behavior. The goal of this dissertation was to create a multi-segment foot model that captures anatomically relevant motion and accurate inter-segmental kinetics, with a primary application of use in clinical gait analysis.
First, relevant literature was used to guide decisions on segmentation and coordinate system definitions. It was decided that a three segment model, which includes a rearfoot, mid/forefoot, and hallux could sufficiently characterize foot function while still allowing for kinetic analysis. Joint centers were chosen to closely match current research, and verified by measuring joint translations during gait. The ankle joint center was moved from its traditional location (between the malleoli) using an anatomical offset developed in a small radiographic study. Increased accuracy was confirmed by a decrease in ankle joint translations during normal gait.
Several possible segment coordinate systems were created and tested for repeatability. From these, a single model was decided upon. This model was further tested for reliability in marker placement, finding mean between-tester segment coordinate system orientation differences that were generally less than 5°. The rigidity of each segment was analyzed using the residual from the segment coordinate system tracking algorithm. The shank and rearfoot showed low residuals (high rigidity), while the forefoot had an increased residual in terminal stance through loading response. The addition of an extra tracking marker on the forefoot did not increase the rigidity of this segment, and rigid body violations should be taken into account when interpreting results from the model.
Ground reaction forces under each segment were measured using a targeted walking approach in conjunction with two adjacent force plates. The targeting approach resulted in minimal differences in overall ground reaction forces compared to non-targeted walking (shear force RMSE < 3%BW). A prevailing theory that subarea ground reaction shear forces can be estimated using a pressure mat combined with a force plate was also tested. This estimation method resulted in errors particularly when opposing shear forces were present, which occurred both between the rearfoot and forefoot and between the forefoot and hallux.
A normal database (N=17) of foot and ankle kinematics and kinetics was created using the foot model and the measured ground reaction forces. Euler/Cardan rotations were chosen to represent joint motion, while traditional inverse dynamics methods were used to calculate joint moments and powers. Of particular interest in normal gait was the large power generation at the midfoot and the apparent power transfer between the toe and midfoot during push-off.
Finally, a single patient exhibiting dynamic hindfoot varus was tested using the model and analysis method to begin showing possible applications in clinical gait analysis. Avenues for future work include additional patient evaluations as well as applications in muscle modeling and forward dynamics.
|Advisor:||Richards, James G.|
|Commitee:||Buczek, Frank L., Higginson, Jill S., Royer, Todd D.|
|School:||University of Delaware|
|Department:||Department of Health, Nutrition and Exercise Sciences|
|School Location:||United States -- Delaware|
|Source:||DAI-B 70/09, Dissertation Abstracts International|
|Subjects:||Biomedical engineering, Biomechanics|
|Keywords:||Foot, Gait, Kinetics, Motion analysis, Multisegment|
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