Bending Vibrations of the Femur and the Oscillatory Behavior of a Cemented Femoral Hip Endoprosthesis

[+] Author and Article Information
M. Thomsen, W. Görtz

Orthopädische Klinik, University of Heidelberg, Heidelberg, Germany

A. Görtz, H. Nägerl

IV. Physikalisches Institut, University of Göttingen, Göttingen, Germany

U. V. Nägerl

Neurology Department, UCLA School of Medicine, Los Angeles, CA 90024

D. Kubein-Meesenburg

Abt. Kieferorthopädie des Zentrums ZMK, University of Göttingen, Göttingen, Germany

J. Fanghänel

Institut für Anatomie, University of Greifswald, Greifswald, Germany

J Biomech Eng 122(4), 416-422 (Feb 28, 2000) (7 pages) doi:10.1115/1.1286317 History: Received March 24, 1998; Revised February 28, 2000
Copyright © 2000 by ASME
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(a) Mechanical arrangement (schematic): A=application point of stimulating force in x direction; B=z positions of the stereo pickups, which record the bone oscillations. Total length of the femur in relation to center M=44.5 cm. (b) Photograph of the mechanical arrangement: a=electrodynamic load-speaker, b=embedding, c=prosthesis head, d=three electrodynamic stereo pickups (to monitor head oscillations), db=two electrodynamic stereo pickups (to monitor bone oscillations). Thickness of the plaster embedding =6 cm.
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(a) Location of the stereo pickups on the prosthesis head. M=center of the prosthesis head and origin of the fixed coordinate system. In each case, the pickups recorded two components of the velocity of the contact points: the components which are (a) perpendicular to the head surface, and (b) parallel to the head surface and perpendicular to the groove of the record piece. (b) Location of the stereo pickups on the bone. B=center of the bone disk.
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Circuit diagram of the analog data processing
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(a) Frequency spectrum of the velocity amplitudes, determined by the six channels of the three stereo pickups at the prosthesis head. Ωi=resonance frequencies. (b) Frequency spectrum of the velocity amplitudes, determined by the four channels of the two stereo pickups on the fermoral bone head. Ωi=resonance frequencies.
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12 Hz vibration. The instantaneous helical axis PH of the head was stationary and medially shifted outside the head. The corresponding instantaneous axis PB was also almost stationary, but laterally shifted. The angular velocities μzb and μzb have the same direction.
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Resonance Ω1: The components of translation and rotation as functions of time for the prosthesis head and the femoral bone (true scale). The phase was related to the stimulating force according to: Fx=−Fxo cos(Ω1t).
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Stationary instantaneous rotational axes of the resonances Ω2=331 Hz (a), Ω3=340 Hz (b), and Ω4=389 Hz (c).




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