Movable Axis Knee Stability Measurement Apparatus
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Solution Overview
Problem
Conventional devices are unable to provide quantitative measurements of individual anterior-posterior stability of the medial and lateral compartments of the knee, nor can they accurately identify the axis of rotation, which is crucial for differentiating the effects of injuries like ACL ruptures and treatments such as ligament reconstruction or joint replacement.
Innovation Solution
An apparatus with a support frame, a movable axis of rotation fixation assembly, and a displacement assembly that allows for the application of pure torques and simultaneous or independent anterior-posterior forces to the knee, enabling the measurement of medial and lateral compartment translations, angle of rotation, and location of the axis of rotation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional measurement devices are used to measure knee rotations about a fixed axis, then the measurement process is simple, but the measurement precision is insufficient because the axis of rotation changes with flexion angle and is affected by injury or treatment
Solution Approach 1:
The apparatus employs a movable axis of rotation that can dynamically adjust its position along the bone rather than being fixed. This dynamic capability allows the measurement system to track the actual changing axis of rotation during joint movement, thereby improving measurement precision while accepting increased device complexity through the use of movable components and sensors
Solution Approach 2:
The measurement apparatus is divided into separate functional modules including the movable axis mechanism, sensors for detecting position and motion, and a control system. This segmentation allows each component to be optimized independently for its specific function, improving overall measurement precision while managing device complexity through modular design
2Measurement precision
If forces are applied to measure overall knee stability, then the measurement process is straightforward, but the measurement precision is insufficient for differentiating medial and lateral compartment stability
Solution Approach 1:
The force application system is segmented into separate actuators that can independently apply forces to the medial and lateral compartments of the knee. This allows for compartment-specific stability measurements by isolating and testing each compartment individually, improving measurement precision while managing device complexity through independent modular actuators
Solution Approach 2:
The apparatus applies forces locally to specific compartments (medial or lateral) rather than applying uniform force to the entire knee joint. This localized force application enables differentiation of compartment-specific stability characteristics, improving measurement precision while requiring a more complex localized force application mechanism
3Measurement precision
If the axis of rotation is fixed and predetermined, then the device complexity is low, but the measurement precision deteriorates because the actual axis of rotation varies with flexion angle and injury condition
Solution Approach 1:
The axis of rotation is implemented as a movable component that can dynamically reposition itself along the bone during joint movement. This dynamic adjustment allows the measurement system to accurately track the actual axis of rotation at different flexion angles and injury conditions, improving measurement precision while necessitating a more complex movable axis mechanism with associated sensors and control systems
Data Source
AI summary
An apparatus for evaluating motions of a joint is provided that is designed for determining stability of an anatomical joint. The apparatus includes a support frame, a fixation assembly for securing a first body segment of a joint, and a displacement assembly mounted to the support frame. The fixation assembly includes an axis of rotation moveable relative to the support frame. The displacement assembly includes a first frame pivotably mounted to the support frame and rotatably connected to a first end of the fixation assembly, and a second frame pivotably mounted to the support frame and rotatably connected to a second end of the fixation assembly.