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Research Papers

Evaluating the Bending Response of Two Osseointegrated Transfemoral Implant Systems Using 3D Digital Image Correlation

[+] Author and Article Information
Melanie L. Thompson, Chris K. Mechefske

Department of Mechanical and Materials Engineering, Queen’s University, McLaughlin Hall, Kingston, ON, K7L 3N6, Canada

David Backman

Institute for Aerospace Research, National Research Council Canada, 1200 Montreal Road, Building M-14, Ottawa, ON, K1A 0R6, Canada

Rickard Branemark

Centre of Orthopaedic Osseointegration Sahlgrenska  University Hospital, Per Dubbsgatan 15, 413 45 Gothenburg, Sweden

J Biomech Eng 133(5), 051006 (Apr 28, 2011) (9 pages) doi:10.1115/1.4003871 History: Received July 23, 2010; Revised March 11, 2011; Posted March 28, 2011; Published April 28, 2011; Online April 28, 2011

Osseointegrated transfemoral implants have been introduced as a prosthetic solution for above knee amputees. They have shown great promise, providing an alternative for individuals who could not be accommodated by conventional, socket-based prostheses; however, the occurrence of device failures is of concern. In an effort to improve the strength and longevity of the device, a new design has been proposed. This study investigates the mechanical behavior of the new taper-based assembly in comparison to the current hex-based connection for osseointegrated transfemoral implant systems. This was done to better understand the behavior of components under loading, in order to optimize the assembly specifications and improve the useful life of the system. Digital image correlation was used to measure surface strains on two assemblies during static loading in bending. This provided a means to measure deformation over the entire sample and identify critical locations as the assembly was subjected to a series of loading conditions. It provided a means to determine the effects of tightening specifications and connection geometry on the material response and mechanical behavior of the assemblies. Both osseoinegrated assemblies exhibited improved strength and mechanical performance when tightened to a level beyond the current specified tightening torque of 12 N m. This was shown by decreased strain concentration values and improved distribution of tensile strain. Increased tightening torque provides an improved connection between components regardless of design, leading to increased torque retention, decreased peak tensile strain values, and a more gradual, primarily compressive distribution of strains throughout the assembly.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 9

Locations of peak tensile and compressive strains for each test group (with 120 lbf applied load). Locations are based on the average of the three samples per test group (V1=hex, V2=taper). Note: Proximal interface of the implant and the abutment are at the left side of the photo.

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Figure 10

Average peak tensile and compressive strains as measured by the DIC system for each test group (condition 7 with 120 lbf applied bending load)

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Figure 11

Torque retention of the original hex and modified taper samples following the completion of all nine load conditions in Table 1

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Figure 7

Example DIC results for condition 7 during 120 lbf applied bending load. (a) hex, 12 N m; (b) hex, 25 N m; (c) taper, 12 N m; and (d) taper, 25 N m.

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Figure 5

Representative DIC outputs for taper (12 N m): εxx response during the nine loading conditions, corresponding to Table 1

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Figure 3

DIC experimental setup at NRC

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Figure 2

The osseointegrated implant parts, each assembly contains three parts: an implant-base (top left), an abutment (top right), and a retention bolt (bottom). (a) Hex connection and (b) morse taper connection.

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Figure 8

Example DIC output of εxx during loading conditions 2 (left), 8 (center), and 9 (right) for each of the four test groups

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Figure 6

Example DIC results for condition 3 during 40 lbf applied bending load. (a) hex, 12 N m; (b) hex, 25 N m; (c) taper, 12 N m; and (d) taper, 25 N m.

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Figure 4

Schematic of the mounting fixture for testing the MCL prototype assemblies in bending (designed by NRC), notation to identify corresponding anatomical planes of motion

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Figure 1

Transverse view of the osseointegration setup

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