Tom Burke

Project Title: Frequency Response as a tool to assess damage within bone structure

Student Name: Tom Burke

Supervisor: Dr. John Hession, Dr. Joe Gildea

Funding Body: Strand 3

Abstract:

Vibration analysis has been used by clinicians for decades in an attempt to assess fracture and integrity.  By stimulating the bone and analyzing the response, it is possible to monitor the structures integrity. A range of pathological conditions may also be monitored, from trauma fractures, to diseases of the bone such as osteoporosis, to the integrity of artificial hip-joint prosthesis.

Resonant Frequencies (RF), Frequency Responses (FR) and Modes of Vibration (MOV) of the structure under an excitation allows the investigator to determine a Transfer Function for a given system, in this case, whole Ovine Tibia. This function, describes the mass, stiffness and damping matrices of the structure under given conditions, i.e. boundary, loading etc.  

This study focuses on using these vibration parameters RF, FR and MOV, to determine the structures mechanical properties, namely Bending Rigidity and Structural Stiffness.

Due to the complex geometry and homogeneity of whole bone, it was necessary to develop a standardized method to keep the experiment as controlled as possible and hold boundary conditions constant such as, points of location, point of excitation, and point of received responses.

The vibration experiment consisted of investigating bone resonant frequencies and responses under predetermined load intervals. Loading was carried out using three point bending in accordance with ASTM E4, and ANSI/ASAE S459.

Excitation was applied using a GW Electromechanical Shaker (Gearing & Watson) and a controlled frequency sweep (Stepped Sine) of known amplitude and force. Excitation was applied to the Articular surface of the Medial Malleolus via an Impedance Head and Stinger arrangement, Fig. 1. The Tibia was held in the normal physiological orientation, under Free-Free boundary conditions, using a custom built Jig.

RF, FR and MOV’s were determined using a Single Input Multiple Output analysis (SIMO). A spectrum analyzer was used as both a data acquisition and processing platform (Brϋel & Kjaer). FR was determined from Bode Plots of each excitation sweep, while changes in RF and MOV were determined from peak amplitude responses displayed on a Frequency (Hz) vs. Magnitude (dB) plot.

Publications/Conferences attended:

22nd Jan 2010                16th Annual Conference Bioengineering, Royal Academy of Medicine.

Frequency Response as a tool to assess damage within bone structure.

28th Nov 2009                 10th Annual Multidisciplinary Research Conference.

Frequency Response as a tool to assess damage within bone structure.

30th Jan 2009                 15th Annual Conference Bioengineering, Royal Academy of Medicine.

Modelling of Crack Propagation in bone using Acoustic Emission, Strain Energy & Vibration.

Fig 1: MOV Shift of Structure & Experimental Setup