Ferrofluid Sensor for Intramedullary Nail Tracking
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Solution Overview
Problem
Electromagnetic Tracking (EMT) systems face challenges in accurately tracking the position and orientation of surgical implants, such as intramedullary nails, due to external forces causing deformation, which can lead to positioning errors when the sensor is not positioned within the clearance hole.
Innovation Solution
A wireless sensor with a ferrofluid core is introduced into the clearance hole of the surgical implant, causing distortion in a magnetic field, allowing field measuring coils to determine the position and orientation of both the sensor and the clearance hole, simplifying tracking and reducing computational requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the sensor is positioned outside the clearance hole, then the tracking system can use simpler hardware, but positioning errors occur due to deformation of the implant under external forces
Solution Approach 1:
The sensor is positioned inside the clearance hole of the implant, nesting the tracking device within the implant structure itself. This ensures that the sensor moves with the clearance hole during deformation, maintaining accurate relative positioning without requiring external mounting structures.
Solution Approach 2:
The clearance hole acts as an intermediary structure that couples the sensor to the implant. By placing the sensor within the clearance hole, the system uses the hole's deformation as a mediator to maintain accurate tracking of the implant's position and orientation even when the implant bends under external forces.
2Measurement precision
If a six degree of freedom (6DoF) sensor is used to track both position and orientation, then tracking precision is improved, but computational power and hardware cost increase
Solution Approach 1:
The system exploits the cylindrical symmetry of the clearance hole and sensor arrangement to eliminate the need for tracking roll orientation. Since the clearance hole is cylindrical, rotation around its axis (roll) does not change the relative positioning, allowing the use of a simpler 5DoF sensor that tracks only position and two orientation components, reducing computational requirements while maintaining tracking precision.
Solution Approach 2:
The tracking system focuses computational resources on measuring the specific degrees of freedom that are relevant to the cylindrical geometry. Instead of uniformly measuring all six degrees of freedom, the system locally adapts the measurement approach to exploit the rotational symmetry, measuring only the necessary orientation components that affect clearance hole positioning.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables precise tracking of the implant's position and orientation, minimizing positioning errors due to deformation, and allows for the use of lower-cost hardware and reduced computational power, while also providing biocompatible and biodegradable options for sensor removal.
Implementation Method 1
Magnetic properties of the sensor are configured to cause distortion in a generated magnetic field, and a field measuring coil is configured to measure characteristics of the distortion
Implementation Method 2
The sensor may include a shell filled with a ferrofluid core
Data Source
AI summary
A system comprising: a sensor configured to be introduced into a clearance hole of a surgical implant, wherein the sensor is configured to be introduced in proximity to a generated magnetic field and cause distortion of the magnetic field; and one or more field measuring coils configured to: measure a characteristic of the magnetic field when the sensor is in proximity to the magnetic field; and provide, to a computing device, a signal representative of the measured characteristic of the magnetic field, wherein the computing device is configured to determine one or both of a position and an orientation of the sensor and the clearance hole based on the measured characteristic of the magnetic field.