Diagnostic prediction of ovine fracture healing outcomes via a novel multi-location direct electromagnetic coupling antenna

Employing direct electromagnetic coupling to assess acute fracture healing: An ovine model assessment

OBJECTIVES

This study explored the efficacy of collecting temporal fracture site compliance data via an advanced direct electromagnetic coupling (DEC) system equipped with a Vivaldi-type antenna, novel calibration technique, and multi-antenna setup (termed maDEC) as an approach to monitor acute fracture healing progress in a translational large animal model. The overarching goal of this approach was to provide insights into the acute healing dynamics, offering a promising avenue for optimizing fracture management strategies.

METHODS

A sample of twelve sheep, subjected to ostectomies and intramedullary nail fixations, was divided into two groups, simulating normal and impaired healing scenarios. Sequential maDEC compliance or stiffness measurements and radiographs were taken from the surgery until euthanasia at four or eight weeks and were subsequently compared with post-sacrifice biomechanical, micro-CT, and histological findings.

RESULTS

The results showed that the maDEC system offered straightforward quantification of fracture site compliance via a multiantenna array. Notably, the rate of change in the maDEC-measured bending stiffness significantly varied between normal and impaired healing groups during both the 4-week (p = 0.04) and 8-week (p = 0.02) periods. In contrast, radiographically derived mRUST healing measurements displayed no significant differences between the groups (p = 0.46). Moreover, the cumulative normalized stiffness maDEC data significantly correlated with post-sacrifice mechanical strength (r2 = 0.80, p < 0.001), micro-CT measurements of bone volume fraction (r2 = 0.60, p = 0.003), and density (r2 = 0.60, p = 0.003), and histomorphometric measurements of new bone area fraction (r2 = 0.61, p = 0.003) and new bone area (r2 = 0.60, p < 0.001).

CONCLUSIONS

These data indicate that the enhanced maDEC system provides a non-invasive, accurate method to monitor fracture healing during the acute healing phase, showing distinct stiffness profiles between normal and impaired healing groups and offering critical insights into the healing process's progress and efficiency.

Ultrasensitive capacitive sensing system for smart medical devices with ability to monitor fracture healing stages

Bone fractures are a global public health problem. A sustained increase in the number of incident cases has been observed in the last few decades, as well as the number of prevalent cases and the number of years lived with disability. Current monitoring techniques are based on imaging techniques, which are highly subjective, radioactive, expensive and unable to provide daily monitoring of fracture healing stages. The development of reliable, non-invasive and non-subjective technologies is mandatory to minimize non-union risks. Delayed healing and non-union conditions require timely medical intervention, such that preventive procedures and shortened treatment periods can be carried out. This work proposes the development of an ultrasensitive capacitive sensing system for smart implantable fixation implants with ability to effectively monitor the evolution of bone fractures. Both in vitro experimental tests and numerical simulations highlight that networks of co-surface capacitive systems are able: (i) to detect four different bone healing phases, capacitance decrease patterns occurring as the healing process progresses and (ii) to monitor the callus evolution in multiple target regions. These are very promising results that highlight the potential of capacitive technologies to minimize the individual and social burdens related to fracture management, mainly when delayed healing or non-union conditions occur.

Direct electromagnetic coupling to determine diagnostic bone fracture stiffness

Background

Rapid prediction of adverse bone fracture healing outcome (e.g., nonunion and/or delayed union) is essential to advise adjunct therapies to reduce patient suffering and improving healing outcome. Radiographic diagnostic methods remain ineffective during early healing, resulting in average nonunion diagnosis times surpassing six months. To address this clinical deficit, we developed a novel diagnostic device to predict fracture healing outcome by noninvasive telemetric measurements of fracture bending stiffness. This study evaluated the hypothesis that our diagnostic antenna system is capable of accurately measuring temporal fracture healing stiffness, and advises the utility of this data for expedited prediction of healing outcomes during early (≤3 weeks) fracture recovery.

Methods

Fracture repair was simulated, in reverse chronology, by progressively destabilizing cadaveric ovine metatarsals (n=8) stabilized via locking plate fixation. Bending stiffness of each fracture state were predicted using a novel direct electromagnetic coupling diagnostic system, and results were compared to values from material testing (MT) methods. While direct calculation of fracture stiffness in a simplistic cadaver model is possible, comparable analysis of the innumerable permutations of fracture and treatment type is not feasible. Thus, clinical feasibility of direct electromagnetic coupling was explored by parametric finite element (FE) analyses (n=1,632 simulations). Implant mechanics were simulated throughout the course of healing for cases with variations to fracture size, implant type, implant structure, and implant material.

Results

For all fracture states, stiffness values predicted by the direct electromagnetic coupling system were not significantly different than those quantified by in vitro MT methods [P=0.587, P=0.985, P=0.975; for comparing intact, destabilized, and fully fractured (FF) states; respectively]. In comparable models, the total implant deflection reduction (from FF to intact states) was less than 10% different between direct electromagnetic coupling measurements (82.2 µm) and FE predictions (74.7 µm). For all treatment parameters, FE analyses predicted nonlinear reduction in bending induced implant midspan deflections for increasing callus stiffness.

Conclusions

This technology demonstrates potential as a noninvasive clinical tool to accurately quantify healing fracture stiffness to augment and expedite healing outcome predictions made using radiographic imaging.

Evaluation of Bone Consolidation in External Fixation with an Electromechanical System

The monitoring of fracture or osteotomy healing is vital for orthopedists to help advise, if necessary, secondary treatments for improving healing outcomes and minimizing patient suffering. It has been decades since osteotomy stiffness has been identified as one main parameter to quantify and qualify the outcome of a regenerated callus. Still, radiographic imaging remains the current standard diagnostic technique of orthopedists. Hence, with recent technological advancements, engineers need to use the new branches of knowledge and improve or innovate diagnostic technologies. An electromechanical system was developed to help diagnose changes in osteotomy stiffness treated with the external fixator LRS Orthofix®. The concept was evaluated experimentally and numerically during fracture healing simulation using two different models: a simplified model of a human tibia, consisting of a nylon bar with a diameter of 30 mm, and a synthetic tibia with the anatomical model from fourth-generation Sawbones®. Moreover, Sawbones® blocks with different densities simulated the mechanical characteristics of the regenerated bone in many stages of bone callus growth. The experimental measurements using the developed diagnostic were compared to the numerically simulated results. For this external fixator, it was possible to show that the displacement in osteotomy was always lower than the displacement prescribed in the elongator. Nevertheless, a relationship was established between the energy consumption by the electromechanical system used to perform callus stimulus and the degree of osteotomy consolidation. Hence, this technology may lead to methodologies of mechanical stimulation for regenerating bone, which will play a relevant role for bedridden individuals with mobility limitations.

Vivaldi Antennas for Contactless Sensing of Implant Deflections and Stiffness for Orthopaedic Applications

The implementation of novel coaxial dipole antennas has been shown to be a satisfactory diagnostic platform for the prediction of orthopaedic bone fracture healing outcomes. These techniques require mechanical deflection of implanted metallic hardware (i.e., rods and plates), which, when loaded, produce measurable changes in the resonant frequency of the adjacent antenna. Despite promising initial results, the coiled coaxial antenna design is limited by large antenna sizes and nonlinearity in the resonant frequency data. The purpose of this study was to develop two Vivaldi antennas (a.k.a., "standard" and "miniaturized") to address these challenges. Antenna behaviors were first computationally modeled prior to prototype fabrication. In subsequent benchtop tests, metallic plate segments were displaced from the prototype antennas via precision linear actuator while measuring resultant change in resonant frequency. Close agreement was observed between computational and benchtop results, where antennas were highly sensitive to small displacements of the metallic hardware, with sensitivity decreasing nonlinearly with increasing distance. Greater sensitivity was observed for the miniaturized design for both stainless steel and titanium implants. Additionally, these data demonstrated that by taking resonant frequency data during implant displacement and then again during antenna displacement from the same sample, via linear actuators, that "antenna calibration procedures" could be used to enable a clinically relevant quantification of fracture stiffness from the raw resonant frequency data. These improvements mitigate diagnostic challenges associated with nonlinear resonant frequency response seen in previous antenna designs.