Tibial Digitizer for Inertial CAS Axis Acquisition
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Solution Overview
Problem
Inertial-based computer-assisted surgery systems face challenges in determining the mechanical axis of the tibia with limited degrees of freedom, necessitating a more efficient method using readily identifiable anatomical reference points.
Innovation Solution
A tibial digitizer tool with an upper and lower mounting end connected by an alignment rod, featuring a self-centering malleoli engaging mechanism and trackable members, is used to determine the mechanical axis by fastening to the tibial plateau and malleoli, and aligning with anatomical landmarks, providing orientation data to the CAS system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If inertial sensors are used in an inertial-based CAS system, then the system can provide portable and flexible navigation capability, but the sensors do not necessarily provide 6 DOF which limits the ability to determine bone orientation
Solution Approach 1:
A mechanical digitizer tool acts as an intermediary between the inertial sensors and the tibia bone. The tool includes a digitizing rod that physically contacts anatomical landmarks (tibial plateau and malleoli) to define the mechanical axis, while inertial sensors mounted on the tool provide orientation data. This intermediary mechanism enables 6 DOF determination despite the inertial sensors alone not providing full 6 DOF capability.
2Measurement precision
If traditional optical CAS navigation systems are used with two optical bone sensors fixed at spaced apart locations, then the tibial mechanical axis can be determined, but the procedure becomes complex and time-consuming
Solution Approach 1:
The invention merges multiple functions into a single integrated digitizer tool: (1) mechanical linkage to define the mechanical axis through anatomical landmarks, (2) mounting mechanism for inertial sensors, and (3) direct registration capability with the CAS system. This consolidation eliminates the need for separate optical bone sensors at multiple locations, reducing procedural complexity while maintaining measurement precision.
3Adaptability or versatility
If inertial sensors are used without a simplified digitization method, then the system has limited capability, but calculating missing DOF using integrated gyroscope and accelerometer readings adds computational complexity
Solution Approach 1:
The mechanical digitizer tool itself provides the missing degrees of freedom through its physical construction. The tool's rigid structure and defined geometry (alignment rod connecting upper and lower reference points) inherently encode the mechanical axis orientation, eliminating the need for complex computational derivation from sensor data alone. The system uses the tool's physical properties to supplement the inertial sensor measurements.
Data Source
AI summary
A method for determining a mechanical axis of a tibia using a tibial digitizer is disclosed. The method includes: determining an upper reference point on a tibial plateau corresponding to an entry point of the mechanical axis; fastening an upper mounting end of the tibial digitizer to the tibial plateau at the upper reference point; and fastening a lower mounting end of the tibial digitizer to medial and lateral malleoli of the ankle, by inwardly displacing opposed caliper arms of a self-centering malleoli engaging mechanism toward each other in a common plane until the caliper arms abut the malleoli. A lower reference point located at a midpoint between the medial and lateral malleoli is then determined by identifying a corresponding midpoint between the caliper arms when they are clamped onto the medial and lateral malleoli.