Knee Arthrometer for ACL Structural Change Quantification
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Solution Overview
Problem
Current devices for preventing ACL injuries are limited in their ability to quantify continuous force-deformation profiles, ensure relaxed muscle states, separate soft tissue deformation from actual bone displacement, and accurately measure tibial shear forces, leading to incomplete assessment of ACL loading during movement.
Innovation Solution
A knee arthrometer that includes force transducers, string potentiometers, skin electrodes, and custom software to record real-time force-deformation data, ensure muscle relaxation, and measure tibial shear force and displacement, while applying a traction force to reduce bone-cartilage contact and prevent weight-induced shear forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing devices measure displacement for a fixed force, then the measurement process is simple, but the ability to quantify continuous force-deformation profile is lost
Solution Approach 1:
The device transitions from static fixed-force measurement to dynamic continuous force-deformation profiling. The actuator applies controlled forces across a range of values while sensors continuously record the corresponding deformation, enabling the construction of complete force-deformation profiles rather than single-point measurements.
Solution Approach 2:
The patent replaces traditional mechanical displacement measurement systems with a integrated force-deformation measurement system that uses sensors and actuators to directly quantify the relationship between applied force and resulting deformation, providing more comprehensive mechanical property assessment.
2Measurement precision
If muscle activation is not monitored, then the testing procedure is simpler, but the ability to ensure relaxed muscle state is compromised
Solution Approach 1:
The system incorporates muscle activation monitoring with feedback control. Sensors detect muscle activation levels during testing, and this information feeds back to the control system to adjust testing parameters or alert operators, ensuring that measurements are taken when muscles are in the desired relaxed state.
Solution Approach 2:
The testing system automatically monitors and verifies its own operating conditions by detecting muscle activation states, eliminating the need for manual assessment of muscle relaxation and ensuring measurement validity through self-verification.
3Measurement precision
If soft tissue deformation is not separated from bone displacement, then the measurement process is simpler, but the accuracy of actual bone displacement measurement is reduced
Solution Approach 1:
The measurement system separates the total observed displacement into distinct components: soft tissue deformation and actual bone displacement. By using multiple sensors and a distributed measurement approach, the system can isolate and measure bone displacement independently from the surrounding soft tissue deformation that occurs during loading.
4Measurement precision
If joint contact forces are not accounted for, then the testing procedure is simpler, but the ability to accurately assess ACL loading is compromised
Solution Approach 1:
The system uses force sensors and mathematical models as intermediaries to indirectly measure and separate joint contact forces from ACL loading. By measuring total joint forces and using biomechanical models to decompose these forces into their components, the system can isolate the specific loading on the ACL from other joint contact forces.
5Measurement precision
If the limb segment weight applies tibial shear force, then the setup is simpler, but the accuracy of pure ACL force measurement is reduced
Solution Approach 1:
The testing system applies counteracting forces to compensate for and eliminate the gravitational effect of limb segment weight. By using actuators to apply equal and opposite forces during testing, the system neutralizes the unwanted tibial shear force generated by limb weight, isolating the pure ACL force response.
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
The knee arthrometer effectively quantifies ACL structural changes over time, providing accurate measurements of knee laxity and detecting potential ACL damage, thereby aiding in the prevention of injuries by identifying overuse mechanisms before catastrophic rupture.
Implementation Method 1
two force transducers
Implementation Method 2
two string potentiometers
Implementation Method 3
two sets of skin electrodes
Data Source
AI summary
Devices and methods are disclosed for quantifying temporal changes in human anterior cruciate ligament (ACL) structural properties, such as Anterior-Posterior tibial shear force (TSF) and Anterior-Posterior tibial shear displacement (TSD) for testing ACL overuse injury during training and minimizing or preventing ACL injury.