Spinal Cage Calibration via Virtual Model
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Solution Overview
Problem
Current cage calibration methods for computer-assisted surgery are inefficient, particularly in sterile environments, as they require cumbersome calibration devices that are not suitable for all cage shapes and can expose patients and staff to unnecessary radiation, and do not allow for stable cage placement or easy measurement of cage length.
Innovation Solution
A computer-implemented method using a pointing device to acquire a cage tip point, end point, and axis, creating a virtual model of the cage that complies with sterility restrictions and allows for accurate calibration without the need for traditional calibration devices, by determining a transformation between coordinate systems to track the cage's shape, position, and orientation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional calibration devices are used for cage calibration, then calibration can be performed, but sterility is compromised and the devices are not suitable for all cage shapes
Solution Approach 1:
The patent creates a virtual model (copy) of the physical cage through image processing and coordinate system transformation. This virtual representation allows calibration without physical contact, maintaining sterility while adapting to any cage shape that can be captured in the image. The virtual model serves as a digital twin that preserves all geometric information of the original cage.
Solution Approach 2:
The patent replaces the mechanical calibration device with an optical/image-based system. Instead of using physical calibration matrices or mechanical measurement tools that require contact with the cage, the system uses 2D images captured by a camera or navigation system, processes them computationally, and derives 3D cage geometry through coordinate transformations. This substitution eliminates sterility concerns while providing universal compatibility.
2Measurement precision
If calibration devices with openings are used to measure cage dimensions, then measurement is possible, but stable cage placement becomes difficult
Solution Approach 1:
The patent captures a 2D image copy of the cage and performs all measurements on this digital representation. The image contains sufficient geometric information to determine cage dimensions, tip position, and orientation. By measuring the virtual copy rather than requiring physical placement in calibration device openings, the system maintains measurement precision without compromising placement stability.
3Adaptability or versatility
If a generic calibration approach is used that allows multiple input options, then flexibility is improved, but calibration complexity increases
Solution Approach 1:
The patent implements a self-calibrating system where the cage itself provides all necessary calibration information through its image. The system automatically detects cage features, establishes coordinate systems, and generates the virtual model without requiring manual input of calibration parameters or user interaction with complex calibration procedures. The cage's own geometry serves as the calibration reference.
4Reliability
If traditional calibration methods are used, then calibration can be performed, but radiation exposure to patient and staff increases
Solution Approach 1:
The patent replaces traditional calibration methods that may involve fluoroscopic imaging or other radiation-based techniques with a pure optical/image processing approach. The system uses 2D images captured during normal surgical navigation (which can be non-radiation-based) and performs all calibration computations digitally. This substitution maintains calibration accuracy while eliminating or significantly reducing radiation exposure.
Data Source
AI summary
A computer implemented medical method of calibrating a cage is presented. In particular, this calibration method calculates a virtual model of the cage based on a cage tip point and a cage end point, acquired by using a pointer tip of a pointing device, and at least one axis, acquired by using a pointer shaft of the pointing device along a side of the cage. This method allows for providing a more detailed virtual model of the cage, while being in compliance with sterility restrictions.