TECHNICAL PAPERS: Bone/Orthopedics

Vibrational Characteristics of Bone Fracture and Fracture Repair: Application to Excised Rat Femur

[+] Author and Article Information
Azra Alizad

Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, 200 First Street SW, Rochester, MN 55905aza@mayo.edu

Matthew Walch1

Department of Agronomy and Plant Genetics, University of Minnesota, St. Paul, MN 55108-6026

James F. Greenleaf, Mostafa Fatemi

Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, 200 First Street SW, Rochester, MN 55905


At Ultrasound Research Laboratory, Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine during the course of this study.

J Biomech Eng 128(3), 300-308 (Dec 09, 2005) (9 pages) doi:10.1115/1.2187037 History: Received May 02, 2005; Revised December 09, 2005

Background. The vibrational characteristics of any object are directly dependent on the physical properties of that object. Therefore, changing the physical properties of an object will cause the object to adopt changed natural frequencies. A fracture in a bone results in the loss of mechanical stability of the bone. This change in mechanical properties of a bone should result in a change of the resonant frequencies of that bone. A vibrational method for bone evaluation has been introduced. Method of approach. This method uses the radiation force of focused amplitude-modulated ultrasound to exert a vibrating force directly, and remotely, on a bone. The vibration frequency is varied in the range of interest to induce resonances in the bone. The resulting bone motion is recorded and the resonance frequencies are determined. Experiments are conducted on excised rat femurs and resonance frequencies of intact, fractured, and bonded (simulating healed) bones are measured. Results. The experiments demonstrate that changes in the resonance frequency are indicative of bone fracture and healing, i.e., the fractured bone exhibits a lower resonance frequency than the intact bone, and the resonance frequency of the bonded bone approaches that of the intact bone. Conclusion. It is concluded that the proposed radiation force method may be used as a remote and noninvasive tool for monitoring bone fracture and healing process, and the use of focused ultrasound enables one to selectively evaluate individual bones.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 1

Rat femur sample in the fixture. The bone is imbedded until the condylus is just covered in the epoxy. L1=length of the femur from fixture to head; L2=length of the femoral shaft; W=width of femur at midpoint.

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Figure 2

Cross section of a femur

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Figure 3

Experimental setup for bone resonance measurement. The ultrasound transducer and laser vibrometer are on opposite sides of the femur. The femur is held by the fixture at the focal point of the transducer. Femur is set with the wide cross section exposed to the laser and the ultrasound beam.

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Figure 4

Picture of the experimental setup in water tank from the laser vibrometer camera. This figure shows the rat femur in its fixture being held by a clamp. Ultrasound transducer is in the background.

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Figure 5

System setup for measuring the frequency response of the bone by the acoustic method

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Figure 6

Frequency response of the intact femur A. The plots show the motion of the intact femur vs frequency. These plots indicate peaks at 925Hz, 4.2kHz, and 8.1kHz. Peaks of motion below 700Hz were explored and found not to be related to the femur. Top left: Driven and measured at the end of the femur at frequency range of 100Hzto1000Hz. Top right: Driven and measured at the end of the bone at 1kHz–10kHz. Bottom left: Driven and measured at bone midpoint at 100Hz–1000Hz. Bottom right: Driven and measured at bone midpoint at 1kHz–10kHz.

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Figure 7

Frequency response of the cut femur A

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Figure 8

Frequency response of the bonded femur A

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Figure 9

(a) Frequency response of the intact femur measured by acoustic method using the system in Fig. 5. (b) Frequency response of the same femur measured by laser vibrometer. (c) Frequency response of the water tank measured by the acoustic method after moving the ultrasound focus away from the bone. The peaks represent the resonance frequency of the water tank. These peaks match with the extraneous peaks seen in (a).



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