Confounding in Electrical Signals of Bone as the Fracture Heals

Diagnostics and prognosis for fracture healing still remains an unanswered problem leading to increased suffering and costs during treatment especially in cases of delayed and/or non-unions. Healing is a continuous process, therefore should be measured on a continuous quantitative scale. Bone is a biological semi-conductor that displays a combination of many electromagnetic properties generated due to piezoelectric and junctional diode effects. Their measurements as the fracture heals could be beneficial but are confounded by the ionic movement (noise) from soft tissue. Fracture type, cross sectional area, diameter, volume and length of bone are possible confounders in electrical measurements in addition to demographics and generic health related parameters of patients. A pilot observational study was designed to measure electrical signals from bone with reduced noise using a bio-compatible insulated external fixator as probe in adult patients with compound fractures of tibio-fibula. Measurements generated by using direct current were unsatable due to ionic movements. An LCR-q meter providing 2μA alternating current gave stable readings in terms of impedance (capacitance, conductance and inductance). The high variance was observed, which could be due to inability of measuring cross sectional area of bone. Interestingly, even though inductance was not a good predictor of healing, it was found to be unaffected by cross sectional area. However, the findings are not robust due to limited data availability, but can be used as a template for further research. The information gathered from this study will be important for development of an instrument to reliably measure fracture healing from bone's electromagnetic characteristics.