Design and Analysis of Orthogonally Compliant Features for Local Contact Pressure Relief in Transtibial Prostheses

[+] Author and Article Information
Mario C. Faustini, Richard R. Neptune

Department of Mechanical Engineering,  The University of Texas at Austin, Austin, Texas 78712

Richard H. Crawford

Department of Mechanical Engineering,  The University of Texas at Austin, Austin, Texas 78712rhc@mail.utexas.edu

William E. Rogers, Gordon Bosker

Department of Rehabilitation Medicine, The University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229

MathWorks, Natick, MA.

Robert McNeel & Associates, Seattle, WA.

Valencia, CA.

South Boston, MA.

J Biomech Eng 127(6), 946-951 (Jul 07, 2005) (6 pages) doi:10.1115/1.2049331 History: Received April 02, 2005; Revised July 07, 2005

A very attractive advantage of manufacturing prosthetic sockets using solid freeform fabrication is the freedom to introduce design solutions that would be difficult to implement using traditional manufacturing techniques. Such is the case with compliant features embedded in amputee prosthetic sockets to relieve contact pressure at the residual limb-socket interface. The purpose of this study was to present a framework for designing compliant features to be incorporated into transtibial sockets and manufacturing prototypes using selective laser sintering (SLS) and Duraform™ material. The design process included identifying optimal compliant features using topology optimization algorithms and integrating these features within the geometry of the socket model. Using this process, a compliant feature consisting of spiral beams and a supporting external structure was identified. To assess its effectiveness in reducing residual limb-socket interface pressure, a case study was conducted using SLS manufactured prototypes to quantify the difference in interface pressure while a patient walked at his self-selected pace with one noncompliant and two different compliant sockets. The pressure measurements were performed using thin pressure transducers located at the distal tibia and fibula head. The measurements revealed that the socket with the greatest compliance reduced the average and peak pressure by 22% and 45% at the anterior side distal tibia, respectively, and 19% and 23% at the lateral side of the fibula head, respectively. These results indicate that the integration of compliant features within the socket structure is an effective way to reduce potentially harmful contact pressure and increase patient comfort.

Copyright © 2005 by American Society of Mechanical Engineers
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Figure 7

(a) Interface contact pressure measured at the distal tibia for both the noncompliant and most compliant sockets; (b) interface contact pressures at the fibula head. (Only the first 10 seconds of data are shown.)

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Figure 6

Results of the topology optimization for an orthogonally compliant test disk for different input volume fractions and their theoretical compliances [as defined in Eq. 3].

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Figure 5

(a) Pressure transducers fixed on the patient’s residual limb at the fibula head and tibial area, (b) compliant socket with corresponding pressure measurement sites indicated, and (c) patient walking using socket with compliant features while limb-socket interface pressure data were collected with a portable data acquisition system.

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Figure 4

(a) Views of a prosthetic socket with complete compliant features incorporated; (b) Section view of socket exposing the compliant features and detailed view of compliant feature

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Figure 3

(a) Section view of the spiral-slotted compliant feature [Fig. 2] and corresponding schematic model of this section of the socket wall passing through the spiral-slotted feature. Note, an orthogonal deflection of center portion is desired while the border is fixed. (b) Definition of the design domain Γ, derived from symmetry through the central vertical plane of a. For the topology optimization problem, material presence is mandatory in the black areas, while material is not allowed in white areas, and gray areas indicate the sections to be optimized.

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Figure 2

(a) Example of orthogonally compliant spiral-slotted features incorporated in a socket; (b) a detailed view of spiral slot compliant feature and a section view showing the void space between the slotted wall and the back protective wall

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Figure 1

(a) A patient using an SLS fabricated socket; (b) description of the parts of a prosthesis for below-the-knee amputees: (i) socket, (ii) attachment fitting, (iii) pylon, and (iv) prosthetic foot



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