MRI Bone-Motion Measurement for Knee Rotation Axis Mapping
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Solution Overview
Problem
Current methods for defining a knee joint rotation axis are inadequate, leading to suboptimal surgical outcomes in total knee arthroplasty due to the complex and variable nature of knee joint movements, which lack a stable rotation axis.
Innovation Solution
A method using MRI to measure relative movement between bones by imaging before and after movement, identifying characteristic subcortical vessels as reference points, and calculating the difference in angles and displacement to determine a stable axis, combined with a computer-aided approach to quantify stability and define individual and population average rotation axes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional definition of rotation axis is applied to knee joint, then the definition is clear for strictly pivotal movement, but the knee joint movement is complex with internal-external rotations and varus-valgus rotations leading to no absolutely stable rotation axis
Solution Approach 1:
The patent transitions from a static rotation axis definition to a dynamic approach by defining the rotation axis as a function of joint angle. The rotation axis position and orientation are determined at multiple joint angles (0°, 30°, 60°, 90°) and interpolated to create a continuous dynamic representation that adapts to the complex kinematics of knee joint movements including internal-external rotations and varus-valgus rotations
Solution Approach 2:
The patent changes the parameter representation of the rotation axis from a fixed geometric entity to a variable defined by joint angle. By expressing rotation axis coordinates (x, y, z) and orientation angles (α, β, γ) as functions of joint angle θ, the system adapts to varying movement conditions while maintaining measurement precision
2Productivity
If no precise definition of knee joint rotation axis is provided, then research can proceed, but the design and placement of artificial joint cannot accurately adapt to individuals during surgery
Solution Approach 1:
The patent performs preliminary action by acquiring and analyzing dynamic MRI data before surgery to determine individual-specific rotation axes at multiple joint angles. This preoperative planning includes creating 3D models, tracking bone movements, and calculating rotation axis parameters that are stored for use during surgical planning and execution, thereby improving both precision and efficiency
Solution Approach 2:
The patent creates accurate digital copies of the patient's knee joint anatomy and movement patterns through MRI imaging and 3D modeling. These digital replicas include bone geometries, soft tissue structures, and movement trajectories that serve as virtual models for preoperative planning and simulation, enabling precise determination of individual rotation axes without requiring complex intraoperative measurements
3Measurement precision
If dynamic MRI imaging at multiple joint angles is performed, then accurate individual rotation axis can be determined, but the imaging process becomes complex and time-consuming
Solution Approach 1:
The patent develops a universal computational framework that handles multiple imaging angles, different bone pairs (femur-tibia, femur-patella), and various movement types through a single integrated system. The software platform performs automated image registration, feature extraction, and rotation axis calculation across all joint angles, reducing the need for separate specialized procedures for each measurement condition
Data Source
AI summary
A method for measuring a relative movement between bones and a method for acquiring a joint rotation axis of bones are provided, which can effectively improve rotational stability of a prosthesis of knee arthroplasty, thereby improving surgical outcomes. A population average bone joint most stable axis (a-MSA) is acquired through the method, so that the design of a joint prosthesis can be improved and a reference of a population average position can be provided for intraoperative placement of a prosthesis. An individual bone joint MSA (i-MSA) of a patient is acquired through the method before surgery, so that individual position information can be provided for intraoperative placement of a prosthesis, thereby further improving rotational stability of a surgical prosthesis.