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Technical Briefs

A Preliminary Biomechanical Assessment of a Polymer Composite Hip Implant Using an Infrared Thermography Technique Validated by Strain Gage Measurements

[+] Author and Article Information
Habiba Bougherara, Ehsan Rahim, Suraj Shah, Anton Dubov, Emil H. Schemitsch

Department of Mechanical and Industrial Engineering,  Ryerson University, Toronto, ON, M5B-2K3, CanadaDepartment of Mechanical and Industrial Engineering,  Ryerson University, Toronto, ON, M5B-2K3, Canada; Martin Orthopaedic Biomechanics Lab, St. Michael’s Hospital, Toronto, ON, M5B-1W8, Canada Martin Orthopaedic Biomechanics Lab, St. Michael’s Hospital, Toronto, ON, M5B-1W8, CanadaMartin Orthopaedic Biomechanics Lab, St. Michael’s Hospital, Toronto, ON, M5B-1W8, Canada; Department of Surgery, Faculty of Medicine,  University of Toronto, Toronto, ON, M5S-1A8, Canada

Rad Zdero1

Department of Mechanical and Industrial Engineering,  Ryerson University, Toronto, ON, M5B-2K3, Canada; Martin Orthopaedic Biomechanics Lab, St. Michael’s Hospital, Toronto, ON, M5B-1W8, Canada e-mail: zderor@smh.ca

1

Corresponding author.

J Biomech Eng 133(7), 074503 (Jul 22, 2011) (6 pages) doi:10.1115/1.4004414 History: Received March 23, 2011; Revised May 26, 2011; Posted June 13, 2011; Published July 22, 2011; Online July 22, 2011

With the resurgence of composite materials in orthopaedic applications, a rigorous assessment of stress is needed to predict any failure of bone-implant systems. For current biomechanics research, strain gage measurements are employed to experimentally validate finite element models, which then characterize stress in the bone and implant. Our preliminary study experimentally validates a relatively new nondestructive testing technique for orthopaedic implants. Lock-in infrared (IR) thermography validated with strain gage measurements was used to investigate the stress and strain patterns in a novel composite hip implant made of carbon fiber reinforced polyamide 12 (CF/PA12). The hip implant was instrumented with strain gages and mechanically tested using average axial cyclic forces of 840 N, 1500 N, and 2100 N with the implant at an adduction angle of 15 deg to simulate the single-legged stance phase of walking gait. Three-dimensional surface stress maps were also obtained using an IR thermography camera. Results showed almost perfect agreement of IR thermography versus strain gage data with a Pearson correlation of R2  = 0.96 and a slope = 1.01 for the line of best fit. IR thermography detected hip implant peak stresses on the inferior-medial side just distal to the neck region of 31.14 MPa (at 840 N), 72.16 MPa (at 1500 N), and 119.86 MPa (at 2100 N). There was strong correlation between IR thermography-measured stresses and force application level at key locations on the implant along the medial (R2  = 0.99) and lateral (R2  = 0.83 to 0.99) surface, as well as at the peak stress point (R2  = 0.81 to 0.97). This is the first study to experimentally validate and demonstrate the use of lock-in IR thermography to obtain three-dimensional stress fields of an orthopaedic device manufactured from a composite material.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Composite hip implant instrumented with strain gages and fixed in a cement-filled steel chamber. A metal ball was inserted at the proximal tip of the hip implant to simulate the femoral head. Black arrows show the strain gage locations 1 to 4.

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Figure 2

Experimental setup used for mechanical cyclic testing of the composite hip implant. Tests were done first with strain gages mounted on the surface of the hip implant and then repeated with strain gages removed while imaging the implant using the IR thermography camera.

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Figure 3

Correlation graph of surfaces stresses from IR thermography vs strain gages. Excellent agreement yielded a Pearson correlation coefficient of R2  = 0.96 and a slope = 1.01 for the line of best fit. Perfect agreement would have give R2  = 1 and slope = 1. All stress values are combined on the graph, regardless of axial force level used or the tensile or compressive nature of the stress. All stresses are Von Mises.

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Figure 4

IR thermography grayscale images of three-dimensional surface stresses on the composite hip implant for the three cyclic force levels of 840 N, 1500 N, and 2100 N. Stresses were extracted from locations 1 to 6 and the “max” point. Locations 1 to 4 corresponded to the strain gage sites. Stress scales given by the camera do not include the maximum or minimum stress values.

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