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Visualizing Diabetic Feet to Optimize Orthotic Fitting

Description

Patients with Diabetes Mellitus (DM) and peripheral neuropathy are at high risk for skin breakdown and subsequent lower extremity amputation due to unnoticed, repeated trauma (plantar pressures) to the plantar foot during walking.  Current rehabilitation methods use subjective methods to fabricate therapeutic footwear in attempts to reduce plantar pressures and prevent skin breakdown, but ulcer recurrence is high (30-57%).   The long term goal of our research is to reduce the incidence of skin breakdown and subsequent amputation by designing and fabricating orthotic devices based on structure, tissue mechanics, and external stresses of the diabetic foot.  

Goals

The first phase of this project focused on structural factors and how they relate to external plantar foot pressures.  During this study we combined spiral x-ray computed tomography imaging methods and plantar pressure analysis to quantify the relationship between internal structure of the foot and external plantar pressure to the foot during loading to improve orthotic design.  The forefoot of each subject was scanned using spiral x-ray computed tomography (SXCT) and plantar pressure was simultaneously recorded in both a loaded and an unloaded condition. (Figure 1). A cohort of subjects with diabetes mellitus and peripheral neuropathy and a matched non-diseased control group were included in the study (Figure 2).  Determining the differences between the Diabetic and healthy foot, and how these differences relate to plantar pressures helps us to understand and manage the structural factors that contribute to skin breakdown.

Figure 1: Subject seated in loading device prior to being CT scanned
Figure 2: Normal foot (a) as contrasted with the structural complications due to diabetes (b)

The second phase of our research is designed to 1) test the efficacy and rationale of selected orthotic designs to distribute pressures evenly on the plantar foot, and 2) develop and test three dimensional (3D) computational models of the foot for enhancing and evaluating a broad range of orthotic device components.  The goal of Aim 1 is to determine the effect of a total contact insert (TCI), a metatarsal pad, and metatarsal pad placement on forefoot plantar pressures and soft tissue deformation.  Combining in-shoe pressure testing with spiral x-ray computed tomography (SXCT) will indicate not only if the orthotic device is effective in reducing forefoot pressures, but also why the orthotic device is effective. The goal of Aim 2 is to develop and validate three-dimensional computational models (Figure 3) for estimating the effects of diabetic foot orthoses on peak plantar pressure and tissue deformation. Structural data from SXCT scans, material properties (plantar soft tissue and orthotic device), and external plantar pressure data from people with DM and peripheral neuropathy will be combined to develop and validate the three-dimensional computational model and methods.  The validated model will be used to predict optimal characteristics of the total contact insert and metatarsal pad (i.e. material properties, size, and placement). The predicted orthotic device will be tested against the traditional orthotic device described in Aim 1 in a new set of patients for its ability to distribute forefoot plantar pressures evenly.  Experimental testing will help to keep computational models realistic and valid while three-dimensional computational modeling will enhance the scientific basis of orthotic design and testing.

Figure 3: Foot geometry is constructed into solid models to facilitate FEA analysis.

Affiliations

Left to Right:  Barna Szabo, Joe Klaesner, Tom Pilgram, Kirk Smith, Jim Blaine, Ricardo Actis, Michael Mueller, Paul Commean, Mary Hastings, Cara Lewis, Dequan Zou, Donovan Lott
Affiliates

Fred Prior, PhD
Department of Radiology
Co-Investigator

Tom Pilgram, PhD
Department of Radiology
Statistician

Paul Commean, BEE
Department of Radiology
Sr. Research Engineer

Kirk Smith, BS
Department of Radiology
Sr. Research Engineer

Michael J. Mueller, PT, PhD
Program in Physical Therapy
Washington University School of Medicine
Principal Investigator

Joseph W. Klaesner, PhD
Program in Physical Therapy
Research Engineer

Dequan Zou, DSc
Program in Physical Therapy
Research Engineer

Mary Hastings, PT
Program in Physical Therapy
Clinical Research

Donovan Lott, PT
Program in Physical Therapy
Clinical Research

Barna A. Szabo, PhD  
Engineering Software Research and Development, Inc.
Co-Investigator

Ricardo L. Actis, PhD
Engineering Software Research and Development, Inc.
Co-Investigator

Liliana Ventura, MSc
Engineering Software Research and Development, Inc.
Research Engineer

Jeffrey Johnson, MD
Department of Orthopaedic Surgery
Consultant

Kent W. Myers
Engineering Software Research and Development, Inc.
Research Engineer

Matthew Silva, PhD
Department of Orthopaedic Surgery
Co-Investigator

Alan Darby, C.Ped.
Wrymark, Inc.
Certified Pedorthist

Support

Funding was provided by the National Center of Medical Rehabilitation and Research, National Institutes of Health (RO1 HD36895).  The authors acknowledge the Prevention and Control Research Core of the Washington University Diabetes Research and Training Center (P60 DK20579) for their assistance in subject recruitment. 

References

  • Mueller, M. J., Hastings, M., Commean, P. K., Smith, K. E., Pilgram, T. K., Robertson, D., Johnson, J. (2003). "Forefoot structural predictors of plantar pressures during walking in people with diabetes and peripheral neuropathy." J Biomech 36(7): 1009-17.
  • Mueller, M. J., Lott, D. J., Hastings, M. K., Commean, P. K., Smith, K. E., Pilgram, T. K. (2006). "Efficacy and mechanism of orthotic devices to unload metatarsal heads in people with diabetes and a history of plantar ulcers." Phys Ther 86(6): 833-42.
  • Mueller, M. J., Smith, K. E., Commean, P. K., Robertson, D. D., Johnson, J. E. (1999). "Use of computed tomography and plantar pressure measurement for management of neuropathic ulcers in patients with diabetes." Phys Ther 79(3): 296-307.
  • Robertson, D. D., Mueller, M. J., Smith, K. E., Commean, P. K., Pilgram, T.,
    Johnson, J. E. (2002). "Structural changes in the forefoot of individuals with diabetes and a prior plantar ulcer." J Bone Joint Surg Am 84-A(8): 1395-404.
  • Smith, K. E., Commean, P. K., Mueller, M. J., Robertson, D. D., Pilgram, T., Johnson, J. (2000). "Assessment of the diabetic foot using spiral computed tomography imaging and plantar pressure measurements: a technical report." J Rehabil Res Dev 37(1): 31-40.
  • Smith, K. E., Commean, P. K., Robertson, D. D., Pilgram, T., Mueller, M. J (2001). "Precision and accuracy of computed tomography foot measurements." Arch Phys Med Rehabil 82(7): 925-9.
  • Bolton, N. R., Smith, K. E., Pilgram, T. K., Mueller, M. J., Bae, K. T.  (2005). "Computed tomography to visualize and quantify the plantar aponeurosis and flexor hallucis longus tendon in the diabetic foot." Clin Biomech (Bristol, Avon) 20(5): 540-6.
  • Commean, P. K., Mueller, M. J., Smith, K. E., Hastings, M., Klaesner, J., Pilgram, T., Robertson, D. D. (2002). "Reliability and validity of combined imaging and pressures assessment methods for diabetic feet." Arch Phys Med Rehabil 83(4): 497-505.
  • Hastings, M. K., Commean, P. K., Smith, K. E., Pilgram, T. K., Mueller, M. J. (2003). "Aligning anatomical structure from spiral X-ray computed tomography with plantar pressure data." Clin Biomech (Bristol, Avon) 18(9): 877-82.