A hydraulic knee joint works by using hydraulic fluid within a cylinder and piston system to control the knee's swing and stance phases, allowing for variable cadence and a more natural gait.
Here's a breakdown of how it works:
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Basic Mechanism: A hydraulic knee joint incorporates a cylinder filled with hydraulic fluid and a piston that moves within the cylinder. This system is connected to the knee's mechanical components.
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Swing Phase Control:
- As the prosthetic leg swings forward, the piston moves within the cylinder.
- The flow of hydraulic fluid is regulated by valves. These valves adjust the resistance, which controls the speed of the swing phase.
- By adjusting the valves, the user can change the knee's swing speed to match their desired walking pace.
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Stance Phase Control (Stance Phase Control Knees):
- More advanced hydraulic knees can also provide stance phase control. Sensors and microprocessors may be used to detect changes in the user's weight and gait.
- The hydraulic resistance can be adjusted to provide stability during the stance phase.
- This can help prevent buckling or falls and improves stability on uneven terrain.
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Variable Cadence: One of the primary advantages of a hydraulic knee joint is its ability to adapt to variable walking speeds. The hydraulic system automatically adjusts the resistance based on the user's pace, providing a more natural and energy-efficient gait.
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Benefits:
- Improved Stability: Hydraulic knees enhance stability, especially during the stance phase.
- Natural Gait: Users can walk with a more natural and fluid gait, closer to their pre-amputation walking pattern.
- Variable Speed: Adaptation to different walking speeds (variable cadence) is a significant advantage.
- Reduced Energy Expenditure: The hydraulic system can reduce the amount of energy the user needs to expend while walking.
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Comparison to Pneumatic Knees: While both hydraulic and pneumatic systems offer variable cadence control, hydraulic systems generally provide greater resistance and stability, particularly for higher-impact activities or users who require more support. Pneumatic systems use air instead of fluid.
In summary, a hydraulic knee joint employs a fluid-filled cylinder and piston to manage the knee's motion, enabling users to walk with greater stability, a more natural gait, and the ability to vary their walking speed. The hydraulic fluid's resistance, controlled by valves, is key to achieving this functionality.
