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TECHNICAL PAPERS: Bone/Orthopedic

Simulation of Fretting Wear at Orthopaedic Implant Interfaces

[+] Author and Article Information
Edward Ebramzadeh1

 Biomechanics Laboratory of the J. Vernon Luck, Sr., M.D. Orthopaedic Research Center, Los Angeles Orthopaedic Hospital∕UCLA and  The Dorr Arthritis Institute of Centinela Hospital, Inglewood, Californiaebramzad@usc.edu

Fabrizio Billi, Sophia N. Sangiorgio, Werner Schmoelz1

 Biomechanics Laboratory of the J. Vernon Luck, Sr., M.D. Orthopaedic Research Center, Los Angeles Orthopaedic Hospital∕UCLA and  The Dorr Arthritis Institute of Centinela Hospital, Inglewood, California

Sarah Mattes2

 Biomechanics Laboratory of the J. Vernon Luck, Sr., M.D. Orthopaedic Research Center, Los Angeles Orthopaedic Hospital∕UCLA and  The Dorr Arthritis Institute of Centinela Hospital, Inglewood, California

Lawrence Dorr3

 Biomechanics Laboratory of the J. Vernon Luck, Sr., M.D. Orthopaedic Research Center, Los Angeles Orthopaedic Hospital∕UCLA and  The Dorr Arthritis Institute of Centinela Hospital, Inglewood, California

1

Biomechanics Laboratory, Los Angeles Orthopaedic Hospital∕UCLA, Los Angeles, California.

2

Sony Picture Imageworks, 9050 West Washington Blvd., Culver City, California 90232.

3

Dorr Arthritis Institute of Centinela Hospital, Inglewood, California.

J Biomech Eng 127(3), 357-363 (Jan 02, 2005) (7 pages) doi:10.1115/1.1894121 History: Received April 25, 2003; Revised January 02, 2005

Osteolysis due to wear debris is a primary cause of failure of total joint replacements. Although debris produced by the joint articulating surfaces has been studied and simulated extensively, fretting wear debris, produced at nonarticulating surfaces, has not received adequate attention. We developed a three-station fretting wear simulator to reproduce in vivo motion and stresses at the interfaces of total joint replacements. The simulator is based on the beam bending theory and is capable of producing cyclic displacement from 3to1000microns, under varying magnitudes of contact stresses. The simulator offers three potential advantages over previous studies: The ability to control the displacement by load, the ability to produce very small displacements, and dynamic normal loads as opposed to static. A pilot study was designed to test the functionality of the simulator, and verify that calculated displacements and loads produced the predicted differences between two commonly used porous ingrowth titanium alloy surfaces fretting against cortical bone. After 1.5 million cycles, the simulator functioned as designed, producing greater wear of bone against the rougher plasma-sprayed surface compared to the fiber-mesh surface, as predicted. A novel pin-on-disk apparatus for simulating fretting wear at orthopaedic implant interfaces due to micromotion is introduced. The test parameters measured with the fretting wear simulator were as predicted by design calculations, and were sufficient to measure differences in the height and weight of cortical bone pins rubbing against two porous ingrowth surfaces, plasma-sprayed titanium and titanium fiber mesh.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic drawing of the three-station fretting simulator assembly. The load cell is mounted above the apparatus, with the actuator on bottom.

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Figure 2

Schematic diagram representing the side view of one of the three stations of the fretting wear simulator. The amount of micromotion at the pin-on-disk assembly can be controlled by adjusting the height of the orange brace. Lowering the height of the brace decreases the bending length of the rod, hence decreasing the amount of motion at the fretting interfaces. The simulator can be adjusted to produce cyclic motion of as little as three microns. (a) A view of the apparatus under no axial loading. (b) How the applied axial load P(P=F∕3) bends the rod, and produces displacement.

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Figure 3

Fretting (tangential) motion of the pin against the disk, for a friction coefficient of 0.3, as a function of effective length of the bending rod, and applied compressive load at the pin-disk interface.

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Figure 4

Height and weight losses for both human and bovine specimens fretting against plasma-sprayed and fiber-mesh titanium ingrowth surfaces. Average height losses for bone fretting against plasma-sprayed versus fiber-mesh specimens are on the left, and average weight losses for the same bone specimens are on the right. Error bars represent the standard deviations.

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Figure 5

Human bone specimens under light microscopy after fretting against fiber-mesh titanium (figure on left) and plasma-sprayed titanium (figure on right) ingrowth surfaces. Titanium particles are visible in both specimens, but are more prevalent in the specimen that fretted against the plasma-sprayed titanium (figure on right).

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