Tibia Cutting Guide Assembly with Inertial Mechanical-Axis Alignment
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Solution Overview
Problem
Inertial-based CAS systems for determining the mechanical axis of the tibia often lack sufficient degrees of freedom, necessitating a simpler and more efficient method to digitize the tibial mechanical axis using readily identifiable anatomical reference points.
Innovation Solution
A tibia cutting guide assembly that utilizes inertial sensors mounted to a guide holder and guide rod, which are aligned with anatomical landmarks such as the tibial tubercle and malleoli, allowing for precise adjustment and fixation to the tibia, enabling accurate orientation and resection planning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional optical CAS navigation systems are used to determine the tibial mechanical axis, then measurement precision can be achieved, but device complexity increases due to requiring two optical bone sensors with six degrees of freedom each
Solution Approach 1:
The patent replaces the complex optical sensor system with inertial sensors that use mechanical integration of accelerometer and gyroscope data to determine the tibial mechanical axis. This substitution reduces device complexity while maintaining measurement precision by using a different physical approach (inertial measurement vs. optical tracking).
Solution Approach 2:
The patent extracts only the essential function needed for mechanical axis determination from the full six-DOF optical sensor system. By using inertial sensors with fewer degrees of freedom and calculating the mechanical axis through integration of linear acceleration and angular velocity data, the system removes unnecessary complexity while preserving the core measurement capability.
2Measurement precision
If inertial sensors with integrated gyroscope and accelerometer readings are used to calculate missing DOF, then measurement capability is maintained, but ease of operation decreases due to complex calculation requirements
Solution Approach 1:
The inertial sensor system performs self-service by automatically integrating accelerometer and gyroscope readings to calculate the mechanical axis and missing degrees of freedom. The system handles the complex calculations internally without requiring manual intervention, thereby maintaining measurement precision while improving ease of operation.
Solution Approach 2:
The patent performs preliminary calibration and setup actions during system initialization, establishing the coordinate systems and sensor orientations before actual measurement begins. This preliminary action reduces the computational burden during operation, making the system easier to use while maintaining accurate mechanical axis determination.
3Ease of operation
If a simpler method to digitize the mechanical axis is sought, then ease of operation improves, but measurement precision may be compromised
Solution Approach 1:
The patent replaces complex optical measurement systems with inertial sensors that offer a simpler operational interface. The inertial sensors directly measure acceleration and rotation, providing a more straightforward method for mechanical axis digitization while maintaining precision through mathematical integration of the sensor data.
Solution Approach 2:
The patent changes the measurement parameters from optical position tracking to inertial acceleration and velocity measurement. By integrating these parameters over time and applying appropriate coordinate transformations, the system achieves accurate mechanical axis determination through a simpler operational process that requires less complex setup and operation.
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
Enables precise and efficient alignment of the tibia cutting guide with the mechanical axis of the tibia, facilitating accurate surgical resection by leveraging inertial sensors for orientation adjustment and fixation.
Implementation Method 1
The device comprises at least a first and a second inertial sensor (1, 2), provided with a triaxial accelerometer and a triaxial gyroscope
Data Source
Figure 1A~1B
Figure 2A~2C
Figure 3A~3B
AI summary
An assembly for positioning a tibia cut guide (10,110,210,310) includes a sensor bracket (314B) with a first inertial sensor (20A). The sensor bracket (314B) is mountable to the tibia (11) at a location thereon representative of a mechanical axis, and mountable to the tibia cut guide (10,110,210,310). An ankle clamp (316C) is mountable non-invasively about a skin (S) of an ankle (A) of a patient to be in fixed relation to the ankle (A) and has a second inertial sensor (20B). The ankle clamp (316C) is spaced apart from the sensor bracket (314B) along a length of a leg and free of interconnection therewith. The first and second inertial sensors (20A,20B) are displaceable with the tibia (11) to register the tibia (11) in a reference coordinate system defined by the first and second inertial sensors (20A,20B), and to calibrate the first inertial sensor (20A) with the mechanical axis.