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Research Papers

Prediction of Plantar Shear Stress Distribution by Artificial Intelligence Methods

[+] Author and Article Information
Metin Yavuz

 Ohio College of Podiatric Medicine, Independence, OH 44131; Department of Chemical and Biomedical Engineering, Cleveland State University, Cleveland, OH 44115; Department of Biomedical Engineering, Cleveland Clinic, Cleveland, OH 44195

Hasan Ocak

Department of Mechatronics Engineering, Kocaeli University, Izmit, Kocaeli 41380, Turkey

Vincent J. Hetherington

 Ohio College of Podiatric Medicine, Independence, OH 44131

Brian L. Davis1

Department of Biomedical Engineering, Cleveland Clinic, Cleveland, OH 44195davisb3@ccf.org

1

Corresponding author.

J Biomech Eng 131(9), 091007 (Aug 06, 2009) (5 pages) doi:10.1115/1.3130453 History: Received October 18, 2007; Revised April 08, 2009; Published August 06, 2009

Shear forces under the human foot are thought to be responsible for various foot pathologies such as diabetic plantar ulcers and athletic blisters. Frictional shear forces might also play a role in the metatarsalgia observed among hallux valgus (HaV) and rheumatoid arthritis (RA) patients. Due to the absence of commercial devices capable of measuring shear stress distribution, a number of linear models were developed. All of these have met with limited success. This study used nonlinear methods, specifically neural network and fuzzy logic schemes, to predict the distribution of plantar shear forces based on vertical loading parameters. In total, 73 subjects were recruited; 17 had diabetic neuropathy, 14 had HaV, 9 had RA, 11 had frequent foot blisters, and 22 were healthy. A feed-forward neural network (NN) and adaptive neurofuzzy inference system (NFIS) were built. These systems were then applied to a custom-built platform, which collected plantar pressure and shear stress data as subjects walked over the device. The inputs to both models were peak pressure, peak pressure-time integral, and time to peak pressure, and the output was peak resultant shear. Root-mean-square error (RMSE) values were calculated to test the models’ accuracy. RMSE/actual shear ratio varied between 0.27 and 0.40 for NN predictions. Similarly, NFIS estimations resulted in a 0.28–0.37 ratio for local peak values in all subject groups. On the other hand, error percentages for global peak shear values were found to be in the range 11.4–44.1. These results indicate that there is no direct relationship between pressure and shear magnitudes. Future research should aim to decrease error levels by introducing shear stress dependent variables into the models.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

The pressure-shear platform and representative placement of foot on the device

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Figure 2

Structure of the feed-forward NN used for the prediction of plantar shear stress

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Figure 3

Correlation of actual and predicted shear stress magnitudes for the diabetic (top) and the athletic (bottom) groups

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Figure 4

Correlation of actual and predicted shear stress magnitudes by NFIS (top) and NN (bottom) for all groups

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Figure 5

Correlation of actual and predicted “peak” shear stress magnitudes by NFIS (top) and NN (bottom) for all groups

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