Modelling the mechano-biological interface changes around transfemoral osseointegrated implants using physical models and detecting the changes with vibration analysis

Cairns, Nicola and Pearcy, Mark and Smeathers, James and Adam, Clayton (2013) Modelling the mechano-biological interface changes around transfemoral osseointegrated implants using physical models and detecting the changes with vibration analysis. In: 5th International Conference: Advances in Orthopaedic Osseointegration, 2013-05-31 - 2013-06-01.

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Abstract

This study investigated the ability of non-invasive vibration analysis to monitor the healing progression of implants in transfemoral amputees. This is an advancement of its application in monitoring dental implant stability. Studies of physical femur-implant models have used vibration to detect interface alterations that only represent gross changes at the interface in vivo. This study describes the development of a series of physical models which simulate incremental interface changes during the progression of osseointegration and the investigation of vibration analysis in detecting the changing conditions. Models were developed to simulate the mechanical characteristics of the femur-implant interface during discrete stages of osseointegration. Forced excitation was applied to the models while their response was measured and used to calculate the dynamic properties of resonant frequency and mode shape. These parameters were compared to ascertain if they uniquely represented each stage. The six resonant frequencies changed depending on the modelled stage of osseointegration. All modes detected fibrous tissue formation. The second bending mode was consistently more sensitive to interface changes than bone mass changes. The first mode shape was similar across all models. In contrast, the second and third mode shapes revealed differences between the stages. The first bending mode was not detectable when the model boundary condition stiffness was decreased. The results indicate that the higher resonant frequencies may be more useful than the first frequency in detecting osseointegration progression. The insensitivity of the second resonant frequency to bone mass changes has important clinical implications; it is essential that in vivo measurements can only be attributed to remodelling at the interface. The mode shapes can be used in conjunction with the resonant frequencies to help identify changes at the interface. The findings demonstrate the potential of vibration analysis for this application and the technique warrants further investigation.