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

Abstract

Background: Expedient prediction of adverse bone fracture healing (delayed-or non-union) is necessary to advise secondary treatments for improving healing outcome to minimize patient suffering. Radiographic imaging, the current standard diagnostic, remains largely ineffective at predicting nonunions during the early stages of fracture healing resulting in mean nonunion diagnosis times exceeding six months. Thus, there remains a clinical deficit necessitating improved diagnostic techniques. It was hypothesized that adverse fracture healing expresses impaired biological progression at the fracture site, thus resulting in reduced temporal progression of fracture site stiffness which may be quantified prior to the appearance of radiographic indicators of fracture healing (i.e., calcified tissue).Methods: A novel multi-location direct electromagnetic coupling antenna was developed to diagnose relative changes in the stiffness of fractures treated by metallic orthopaedic hardware. The efficacy of this diagnostic was evaluated during fracture healing simulated by progressive destabilization of cadaveric ovine metatarsals treated by locking plate fixation (n=8). An ovine in vivo comparative fracture study (n=8) was then utilized to better characterize the performance of the developed diagnostic in a clinically translatable setting.In vivo measurements using the developed diagnostic were compared to weekly radiographic images and postmortem biomechanical, histological, and micro computed tomography analyses.Results: For all cadaveric samples, the novel direct electromagnetic coupling antenna displayed significant differences at the fracture site (P<0.05) when measuring a fully fractured sample versus partially intact and fully intact fracture states. In subsequent in vivo fracture models, this technology detected significant differences (P<0.001) in fractures trending towards delayed healing during the first 30 days post-fracture.Conclusions: This technology, relative to traditional X-ray imaging, exhibits potential to greatly expedite clinical diagnosis of fracture nonunion, thus warranting additional technological development.

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

“…Future studies are therefore recommended for evaluating the applicability of the miniaturized antenna for predicting healing induced bone fracture stiffness progression. These results nonetheless agree with previous antenna development studies [25], which were foundational to the development of subsequent clinical diagnostic devices [26,27]. Previous antenna designs were notably limited by highly nonlinear antenna sensitivity, as a function of initial antenna-implant distance, which made clinical implementation of this technology challenging.…”

“…To address these challenges, a diagnostic antenna system was developed for noninvasive quantification of relative changes in fracture stiffness for any case treated with off-theshelf metallic orthopaedic hardware [25][26][27]. This diagnostic device utilized a coiled coaxial dipole antenna design to directly electromagnetically couple (DEC) to metals in its near-field, thus enabling detection of displacements of metallic implant hardware [25].…”

“…Resultant deflections produced a measureable change in the resonant frequency of the antenna, where the magnitude of implant deflections were a function of the fracture stiffness, a direct measure of healing. This technology has exhibited aptitude in quantifying relative changes in healing fracture stiffness in translational cadaveric [26] and in vivo fracture models [27].…”

Direct electromagnetic coupling to determine diagnostic bone fracture stiffness

“…The LCP was secured to the mid-diaphysis with eight bicortical locking screws (3.5 mm diameter, 316 L SS). The middle screw hole was filled with a locking screw head (i.e., screw threads removed leaving only the locking head) to facilitate subsequent ostectomy at the LCP midspan and to maintain consistent methods to prior analogous tests ( 57 ) ( Figure 1A ). Overlaying soft tissue was restored using standard suturing techniques.…”

“…Coiled coaxial DEC antennas have demonstrated efficacy in quantifying relative changes in fracture stiffness in cadaveric ( 56 ) and in vivo fracture models ( 57 ). However, the original DEC antenna design was limited by reduced antenna sensitivity and a large antenna size.…”