Extending structural health monitoring concepts for bone healing assessment

Abstract

A B S T R A C T A series of experimental investigations are performed to show the potential of integrating sensing elements into an external fixation for healing assessment of a fracture femur. This investigation is supported by finite element analyses that highlight the fundamental structural dynamics, which enable a stiffness-based healing assessment methodology. A saw-bone femur externally fixated with a Hoffman II will be subjected to an artificial fracture. The healing of the fractured femur is simulated with the curing of epoxy applied to the fractured region. The finite element analyses results will help determine the useful modes for assessing the state of healing of the fracture that can be attributed to the changes in the stiffness of the fixated structure. The findings will be tested against a set of experiments to show how the stiffness-related quantities can be delineated from the dynamic response. The results reported will show distinct changes to the frequency response functions as the epoxy cures demonstrating the potential of integrating sensors onto an external fixation for healing and fracture union assessment.Keywords bone fracture; bone healing assessment; structural health monitoring. N O M E N C L A T U R E(x,y,z) = Cartesian coordinate system ρ = density E = Young's modulus ν = Poisson's ratio f = frequency Z tf ( f ) = transfer function v force (t) = voltage time series from force transducer attached to impactor (load cell) v PVDF (t) = voltage time series from polyvinylidene fluoride sensor (film sensor) vˆf orce f ð Þ = voltage amplitude in frequency domain from force transducer attached to impactor vˆP VDF f ð Þ = voltage amplitude in frequency domain from polyvinylidene fluoride sensor ε(t) = strain time series ε s (f) = strain spectrum i(t) = input force time series Iˆf ð Þ = input force spectrum K force = force constant K PVDF = strain constant

Healing assessment of fractured femur treated with an intramedullary nail

“…The B&K Photon + has an internal analogue filter and a 160 dB/octave line-phase digital filter to present aliasing and phase distortion. Unlike previous works, 5,16 the forcing was applied without the use of an instrumented forcing device. Instead, the two-sensor system measures the dynamic response of the fixated femur and along with a statistical assessment of the validity of the data acquired.…”

“…Furthermore, these assessments are correlated to clinical findings that involve patients' verbal description on weight-bearing pain to associate bone healing which is often inaccurate in determining the state of healing and union of the fracture. 5 Therefore, there is currently no robust or reliable method to adequately quantify the load sharing between the internal fixation and bone during different stages of healing.…”

Non-radiative healing assessment techniques for fractured long bones and osseointegrated implant

“…In the work funded by the United States Office of Naval Research (ONR), Ong et al [44] indicated that there is a strong dependence of dynamic response on structural properties of a given construct. In the recent research funded by ONR, Ong et al [44,45] proposed a concept of integrating the sensing elements into external fixation to monitor fracture healing remotely. In their research [44], the potential of locating sensors on the external fixation and the appropriate frequency range were conceptualised using a series finite element analysis.…”

“…In the recent research funded by ONR, Ong et al [44,45] proposed a concept of integrating the sensing elements into external fixation to monitor fracture healing remotely. In their research [44], the potential of locating sensors on the external fixation and the appropriate frequency range were conceptualised using a series finite element analysis. This is then substantiated with a series of experimental study.…”

“…This is then substantiated with a series of experimental study. Ong et al [44] reported that the lower modes are dominated by the deformation of the external fixation and are insensitive to the bone structural change. In the frequency bandwidth between 200 and 400 Hz, these higher order modes were sensitive to the mechanical properties changes in the fracture region (see Fig.…”