Actuator Knee Exercise Device with Load Cell Feedback
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Solution Overview
Problem
Current rehabilitation methods for total knee replacement (TKR) patients face challenges in achieving full range of motion due to scar tissue formation and pain, with existing devices like continuous passive motion machines lacking precision and variability in pressure application, leading to inadequate rehabilitation outcomes.
Innovation Solution
An exercise device with an actuation member and load cell that provides controlled and variable pressure to enhance knee joint mobility, incorporating a control method that adjusts therapy parameters such as extension and flexion angles, forces, and hold times to minimize pain and promote fluid drainage, allowing for progressive increase in range of motion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If early range of motion therapy is applied to prevent scar tissue formation, then mobility recovery is improved, but patient pain increases significantly
Solution Approach 1:
A gel pad is introduced as an intermediary between the actuation member and the patient's limb. The gel pad distributes pressure evenly across the contact surface, preventing localized high-pressure points that would cause pain while still delivering sufficient force to move the joint through its range of motion. This mediator allows early therapy to proceed without exceeding the patient's pain threshold.
Solution Approach 2:
The system dynamically adjusts therapy parameters including force magnitude, application duration, and frequency based on patient tolerance. The controller monitors patient response and modifies these parameters in real-time, enabling progressive increase in therapy intensity while maintaining comfort. This allows mobility recovery to accelerate without proportionally increasing pain.
2Length of moving object
If high pressure is applied to achieve full range of motion, then joint mobility is improved, but risk of additional injury increases
Solution Approach 1:
Load cells are integrated into the actuation member to provide real-time feedback on the force being applied to the patient's limb. This feedback loop allows the controller to monitor joint resistance and stop or reduce pressure if abnormal resistance is detected, preventing excessive force that could cause injury. The system can distinguish between normal tissue resistance and abnormal resistance indicating potential injury risk.
Solution Approach 2:
The system transitions from static, fixed-pressure application to dynamic, adaptive pressure control. The actuation member adjusts force magnitude and application timing based on real-time conditions, allowing the joint to be moved through its available range of motion safely while preventing force that would exceed tissue tolerance. This dynamic control enables achieving greater range of motion without proportionally increasing injury risk.
3Device complexity
If continuous passive motion machines are used for rehabilitation, then device simplicity is maintained, but treatment precision and variability are insufficient
Solution Approach 1:
Traditional mechanical CPM machines with fixed linkages and manual controls are replaced with a motorized actuation system controlled by a microprocessor. This substitution enables precise electronic control of force application, timing, and duration while maintaining the passive motion concept. The system can deliver highly variable and precise pressure profiles that were impossible with purely mechanical systems, yet remains relatively simple in overall architecture.
Solution Approach 2:
The actuation member is designed to perform multiple functions: applying compressive force, providing shear force, and controlling joint movement through various ranges of motion. This multi-functional design consolidates what would otherwise require multiple separate devices or manual techniques into a single automated system, maintaining simplicity while achieving precision and variability in treatment delivery.
Data Source
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AI summary
The present teachings provide for an exercise device (610) for exercising a joint and a limb. The device (610) includes an actuator (730), a foot plate (664), a foot plate load cell (636), and a restrictor (670). The actuation member (630) is rotatable about a rotation axis (X). The actuation member (630) includes a first portion (632) and a second portion (634) that is movable in a direction perpendicular to the rotation axis (X). The foot plate (664) is at a distal end of the second portion (634) of the actuation member (630). The foot plate load cell (636) is mounted to the foot plate (664) and is configured to measure force exerted on the foot plate (664). The restrictor (670) is configured to restrict movement of the second portion (634) of the actuation member (630) and the foot plate (664) at the distal end thereof in the direction perpendicular to the rotation axis (X) unless force exerted on the foot plate (664) exceeds a predetermined force.