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 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.
Reference No.: 2020-004 (18-053 / 17-066)
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 the 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 described herein circumvents these inherent shortcomings by measuring changes in load-sharing between the stabilizing hardware and the healing tissue.
When a fracture is stabilized with a fixation plate or intramedullary nail, the implant first carries a high share of the load. As the bone heals, the share of the load on the plate decreases; therefore, the load measurements can be used to monitor the healing process and inform doctors on the proper course of treatment. Researchers at Colorado State University have done just that with the development of a non-invasive measurement system capable of wirelessly measuring the load on metallic orthopedic hardware (or fixation plate) implanted in patients 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. The electromagnetic profile of the antenna is sensitive to the movement of objects in the near field range. For example, the displacements of the metal due to loading causes 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, an antenna is held against a patient’s extremity such that a metal implant is in the near-field range of the antenna and loading 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. Allowing doctors to assess whether a fracture is healing properly, or if further intervention is necessary.
The technology also has potential use in detecting loosening of orthopedic implants, for example, in total joint replacements. Since the antenna is sensitive to displacements of the hardware, the increased displacements of a loose implant can be detected.
- No internal sensor required
- Cost effective
- No alterations to existing implants
- Eliminates any regulatory hurdles
- Orthopedic fracture healing monitoring
- Detection of loosening orthopedic implants
- Research development
Labus KM, Sutherland C, Notaros BM, Ilic MM, Chaus G, Keiser D, Puttlitz CM. “Direct Electromagnetic Coupling for Non-Invasive Measurements of Stability in Simulated Fracture Healing.” J. Orthop. Res. 2019. 37(5):1164-1171.
Labus KM, Notaros BM, Ilic MM, Sutherland C, Holcomb A, Puttlitz CM. “A Coaxial Dipole Antenna for Passively Sensing Object Displacement and Deflection for Orthopaedic Applications.” IEEE Access. 2018. 6:68184-68194
Last updated: February 2020
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