Inertial Sensor Hip-Knee-Angle Verification Device
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Solution Overview
Problem
Current computer-assisted surgery systems, particularly those using inertial-based sensors, face challenges in accurately determining the mechanical axis of the femur and hip-knee-ankle angle without requiring distally extending drop-rods or other physical components clamped to the ankle, necessitating a more efficient and minimally invasive method for digitizing these parameters during knee replacement surgery.
Innovation Solution
A verification device equipped with inertial sensors and a visual alignment guide, including a laser emitting element, that communicates with the CAS system to determine the mechanical axes of the femur and tibia, allowing for precise calculation of the hip-knee-ankle angle without physical components at the ankle, using MEMS-based trackable members for orientation data and pivotable adjustments to align with anatomical landmarks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional optical CAS navigation systems use two optical bone sensors fixed to the bone at spaced apart locations, then the femoral mechanical axis and hip-knee-ankle angle can be determined, but the device complexity and number of components increase
Solution Approach 1:
The patent extracts the essential function of mechanical axis determination from complex multi-sensor systems. By using a single inertial sensor unit that can determine the femoral mechanical axis through alternative calculation methods (using integrated gyroscope and accelerometer readings), the system removes the need for multiple optical sensors while maintaining measurement capability.
Solution Approach 2:
The inertial sensor unit serves multiple functions: it determines orientation, calculates mechanical axis, and provides navigation data. This multi-functional approach replaces the need for separate optical sensors at multiple locations, reducing overall system complexity while maintaining measurement precision.
2Device complexity
If inertial sensors are used in an inertial-based CAS system, then the system is simpler and more efficient, but the sensors do not necessarily provide six degrees of freedom
Solution Approach 1:
The patent changes the parameter representation from requiring direct six-DOF sensor output to calculating equivalent six-DOF information through integration of gyroscope and accelerometer readings. This parameter transformation allows inertial sensors to provide the necessary orientation and position data without directly measuring all six degrees of freedom.
Solution Approach 2:
The patent introduces calculation algorithms as an intermediary between the inertial sensors and the final orientation/position determination. Instead of relying on sensors to directly provide six-DOF data, the system uses integrated readings from gyroscope and accelerometer to calculate the necessary orientation parameters, bridging the gap between simplified sensor input and comprehensive navigation output.
3Measurement precision
If a distally extending drop-rod or other physical components are clamped to the ankle, then the mechanical axis of the tibia can be digitized, but the procedure becomes more invasive
Solution Approach 1:
The patent extracts the essential measurement function from invasive physical components like drop-rods. By using non-contact or minimally contact methods with inertial sensors and calculation algorithms, the system determines the tibial mechanical axis without requiring distally extending components clamped to the ankle, thereby eliminating the harmful invasiveness while maintaining measurement precision.
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 quick, accurate, and repeatable digitization of the mechanical axes and hip-knee-ankle angle, ensuring correct alignment and implant positioning during knee replacement surgery, reducing invasive procedures and improving surgical precision.
Implementation Method 1
a laser emitting element operable to project a laser beam
Implementation Method 2
The device includes a first micro-electro-mechanical sensor (MEMS) disposed within the mounting base and a second MEMS disposed within the visual alignment guide element
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
The disclosed device for verifying a hip-knee-ankle angle includes a mounting base having a planar abutting surface adapted for direct abutting against a resected surface on a distal femur, and a first inertial sensor in communication with a computer assisted surgery (CAS) system to determine an orientation of the mounting base and to digitize a mechanical axis of the femur. A visual alignment guide element is pivotably mounted to the mounting base such that the angular position of the visual alignment guide element is adjustable so as to be visually aligned with a mechanical axis of a tibia. A difference between orientations of the mounting base and the visual alignment guide is calculated by the computer assisted surgery system to determine the hip-knee-ankle angle. The visual alignment guide may include a second inertial sensor and/or a laser emitting element.