Home-based monitoring of fracture healing has the potential of reducing routine follow-up and improve personalized fracture care. Implantable sensors measuring electrical impedance might detect changes in the electrical current as the fracture heals. The aim was to investigate whether electrical impedance correlated with radiographic fracture healing. Eighteen rabbits were subjected to a tibial osteotomy that was stabilized with an external fixator. Two electrodes were positioned, one electrode placed within the medullary cavity and the other on the lateral cortex, both three millimeters from the osteotomy site. Transverse electrical impedance was measured daily across the fracture site at a frequency range of 5 Hz to 1 MHz using an Analog Discovery 2 Oscilloscope with Impedance Analyzer. Biweekly x-rays were taken and analyzed blinded using a modified anterior-posterior (AP) radiographic union score of the tibia (RUST). Each animal served as its own control by performing repeated measurements from time zero until the end of follow-up.Introduction and Objective
Materials and Methods
Limb-lengthening nails have largely replaced external fixation in limb-lengthening and reconstructive surgery. However, the adverse events and high prevalence of radiological changes recently noted with the STRYDE lengthening nail have raised concerns about the use of internal lengthening nails. The aim of this study was to compare the prevalence of radiological bone abnormalities between STRYDE, PRECICE, and FITBONE nails prior to nail removal. This was a retrospective case series from three centres. Patients were included if they had either of the three limb-lengthening nails (STYDE, PRECICE, or FITBONE) removed. Standard orthogonal radiographs immediately prior to nail removal were examined for bone abnormalities at the junction of the telescoping nail parts.Aims
Methods
In 2019, Lin et al. published a proof-of-concept study of electrical impedance spectroscopy as a simple and low-cost method to characterize progression of fracture repair (Lin et al., Sci Rep 2019). However, the electrical impedance sensors were placed in the fracture site which may impair the transfer to clinical use. To further explore the concept of monitoring fracture healing by electrical impedance spectroscopy, we established a tibial fracture model in the rabbit where sensors are positioned in proximity to the fracture site but without being placed in the fracture site. The aim of this pilot study was to explore whether distinct patterns of electrical impedance would evolve as tibial fractures in rabbits were evaluated until radiographic signs of healing. Approval was granted from the Inspectorate of the Animal Experimentation under the Danish Ministry of Justice. Four rabbits were anaesthetized, and in each rabbit a tibial osteotomy was made and stabilized by an external fixator. Electrical impedance was measured immediately postoperative and hereafter daily until euthanization after 3 weeks. Recordings were obtained within a wide frequency range (10 Hz to 1 MHz) from an inner electrode placed into the medullary canal and an outer electrode placed extracortical on the lateral with a distance of 3 mm to the defect. A similar pattern of electrical impedance over time was observed in the four rabbits. During the very early stages of fracture healing, an initial fluctuation in electrical impedance occurred. However, after 10 days the curves revealed a steady daily increase in electrical impedance. The first radiological signs of bone healing were detected after 14 days and progressed in all four rabbits in accordance with increments in the electrical impedance until termination of the pilot study after 21 days. Consistent electrical impedance patterns were detected during bone healing in a pilot study of four rabbits. Further research is needed to explore whether the presented method of electrical impedance measurements can be used to monitor bone healing over time.
Electrical impedance spectroscopy measurements might be used for real-time monitoring of bone healing. Differences in electrical characteristics of different tissues during fracture healing can provide information of the tissue composition within the fracture region. This concept embraces the digital revolution of orthopaedics allowing for a sensor-based and home-based monitoring of bone healing. Furthermore, real-time monitoring will allow individualized and timely treatment adjustments to prevent bone healing complications. However, electrodes must be placed at a distance to the fracture site in order not to interfere with bone healing. Therefore, we investigated whether longitudinal and transverse electrical impedance measurements from electrodes placed at a distance to the bone defect can detect differences between intact bone and bone defects in vivo. Approval was granted from the Inspectorate of the Animal Experimentation under the Danish Ministry of Justice. Six rabbits were anaesthetized and had both tibias subjected to an osteotomy protocol where first the medial, then the lateral, and final the posterior cortex were removed resulting in a complete 2 mm bone defect. Electrical impedance was measured prior to and after each step of the osteotomy protocol. Recordings were obtained at different frequencies (10 Hz to 1 MHz) from an inner electrode placed into the medullary canal and two different electrodes placed extracortical on the lateral and posterior bone with a distance of 5 mm to the defect. For each rabbit, one tibia had measurements with a free inner electrode and the other tibia had measurements both with a nail and an isolated nail. For all tibias, the intact bone resulted in higher impedance compared with the complete defect, and this difference was most pronounced in the frequency range of 1 kHz to 100 kHz. This applied for all types of internal electrodes including electrode, nail, isolated nail. The isolated nail showed the biggest impedance difference between the intact bone and the complete defect. Incomplete bone defects had lower impedance compared with intact bone, but no consistent pattern for differences in impedance was observed between the different applied defects. Consistent impedance differences between intact bone and complete defects were detected in-vivo in rabbits. Further research is needed to explore whether the presented method of electrical impedance measurements can be used to characterize bone healing over time.
