Telemetric Load-Sensing for the Monitoring of Orthopedic Fracture Healing
Figure 1. An antenna measures the load on a fixation plate used to stabilize a fractured bone. The compressive load on the bone causes the plate to bend, and the resulting displacement of the plate relative to the antenna is detected as a shift in the antenna’s resonant frequency.
At A Glance
Researchers at Colorado State University in collaboration with Bilkent University in Turkey have developed a system and methods to monitor orthopedic fracture healing. The system uses an electromagnetic antenna to measure changes in the near-field interference of metallic orthopedic implants due to deformation of the implants caused by mechanical loads. This measurement reports on the compliance of the fracture site and therefore the progress of healing.
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Currently, after orthopedic surgery, radiographs are used to monitor fracture healing. X-rays use attenuation to provide images of the bone and healing tissue, as attenuation is related to the density of the material. X-rays, however, are unable to discern if a fracture is healing properly in the early post-operative period because there is little to no mineralized tissue in the healing fracture callus (tissue). Furthermore, it would be advantageous to decrease both patient and technician unnecessary exposure to radiation.
The technology developed herein circumvents these inherent shortcomings by measuring changes in load-sharing between the stabilizing hardware and the healing tissue.
The wireless measurement system was developed to sense the load on metallic orthopedic hardware implanted in patients, which can be used to monitor fracture healing. As the implanted hardware is loaded, the material experiences deformations and displacements due to bending that are proportional to the load. These displacements are detected by an electromagnetic antenna, sensitive to the movement of objects in the near field range. More specifically, the displacements of the metal due to loading cause a shift in the resonant frequency of the antenna as measured by the S-parameter. The frequency shift is calibrated to determine the load on the implant. Therefore, when the antenna is held against a patient’s extremity such that the metal implant is in the near-field range of the antenna, loading of the extremity causes displacements of the implant relative to the antenna. The resonant frequency shifts of the antenna are used to measure the load on the implant.
Data has shown that the frequency shift can be used to detect the stabilization of bone, with an increasing frequency shift corresponding to an increasingly unstable construct. This also corresponds to an increase in the maximum principal strain measured on the plate, showing that as the bone becomes less stable, the load on the plate increases. These data indicate that this telemetric sensing technology can be used to measure the load on the fixation plate itself, which can be applied to monitor fracture healing.
- No internal sensor required (implant itself provides the signal)
- Requires no alterations or additions to existing implants
- Eliminates any regulatory approval hurdles
- Cost effective
- Orthopedic fracture healing monitoring
- Detection of loosening orthopedic implants (e.g., joint replacements)
- Research development
Last updated: June 2021
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#CSUInvents – #TechTuesday! Currently, there is no way to accurately monitor fracture healing in the early post-operative period. Researchers at CSU Walter Scott, Jr. College of Engineering have developed a novel method and apparatus to solve this problem. Check out this #patentpending telemetric load-sensing #orthopaedics device invented by Christian Puttlitz, Kirk McGilvray, and Kevin Labus in the Orthopaedic Bioengineering Research Laboratory at Colorado State University.