Researchers at Colorado State University have developed a non-invasive system that uses near-field electromagnetic sensing to monitor fracture healing through implanted hardware. An antenna couples to metallic implants and detects load-induced deflection through shifts in resonant frequency. These shifts are calibrated to quantify implant load and effective limb stiffness. Repeated measurements enable longitudinal tracking of callus formation and load transfer. The system also identifies abnormal micromotion associated with implant loosening.
Accurate assessment of fracture healing requires understanding the evolving mechanical load-sharing between fixation hardware and regenerating bone. Conventional imaging modalities (e.g., X-ray, CT) provide structural information but limited quantitative insight into mechanical stability. Instrumented implants can measure strain directly but introduce design complexity, cost, and regulatory challenges. A non-contact method that quantifies implant deformation and load transfer would provide a clinically practical solution for early detection of delayed union or fixation failure.
When a fracture is stabilized with a fixation plate or intramedullary nail, the implant initially carries most of the mechanical load. As the bone heals, it progressively assumes a greater share of the load, reducing the stress on the implant. Measuring these load changes provides an effective way for doctors to monitor healing and guide treatment decisions.
Under load, the implanted hardware experiences bending and corresponding deformations that are proportional to the applied force. These displacements are detected using an electromagnetic antenna, which is highly sensitive to movement within its near-field range. Specifically, the bending of the metal implant causes measurable shifts in the antenna’s resonant frequency, observed through S-parameter measurements. These frequency shifts are then calibrated to quantify the load on the implant.
In clinical use, the antenna is positioned against a patient’s extremity so that the implant lies within its near-field. Loading the extremity produces displacements of the implant relative to the antenna, generating resonant frequency shifts that correspond to the implant load. This approach allows doctors to assess whether a fracture is healing properly or if additional intervention may be necessary.
The technology can also detect loosening in orthopedic implants, such as total joint replacements. Because the antenna is sensitive to hardware displacements, increased movement associated with a loose implant can be detected, enabling early identification and timely clinical response.
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Christian M Puttlitz
Kevin M Labus
Steve Foster
Steve.Foster@colostate.edu
970-491-7100