hydraulic knee joint

Hydraulic system prosthesisHYDRAULIC SYSTEM PROSTHESIS

PRESENTED BY:MALEEHA NAEEMORTHOTIST & PROSTHETIST

Hydraulics

• Hydraulics is a topic in applied sciences and engineering dealing with the mechanical properties of liquids or fluids.

Components

• Laminated socket• Hydraulic knee unit• Pylon• SACH foot

Hydraulic knee joint

• Hydraulic knees allow adjustment of walking speed by the use of hydraulics (liquid) within the knee.

• Hydraulics can be used with polycentric knees.

Patient compatibility level

• This type of knee is often used for more active patients who vary their walking speeds and do not need assistive walking devices.

Components

• Piston• Knee bolt• Cylinder• Hole

Hydraulic cylinder

Mechanism of Action

• The piston is attached to a pivot in the thigh section of the prosthesis behind the knee bolt, and the cylinder is attached to a pivot in the shank. Because of the way oil acts when forced through a small hole the amount of resistance required for a given velocity of walking is provided automatically.

Features

• As a person’s walking speed increases or decreases, the hydraulics adjust to control the speed at which the shin of the prosthesis swings forward and bends backwards.

Features

“Stumble Recovery” Or A Braking Mechanism: • To prevent buckling of the knee when weight

is on the knee.• The knee has the ability to be locked so that it

will not bend. This may be used if someone is standing for long periods of time

Features

Sensing point:• This has an developed mechanical sensor. • This detects the position of the ground reaction force around the sensing point• Automatically control the knee’s stability.

Gait Analysis

At heel contact

• The system immediately locks the knee joint for the user’s safety

• Limits knee flexion to a maximum 10 degrees.Benefits:• Appropriate amount of stance flexion provides

a comfortable walking. • Amount of the Stance-Flexion is adjustable

according to the user’s gait.

At late stance

• System detects ground reaction force at toe• The knee joint naturally releases the lock• Smoothly shifts to the swing phase.Benefit:• No special gait training is required to the user

for releasing the lock at terminal stance.• System seamlessly releases the lock.

At swing phase

• A compact and powerful hydraulic cylinder naturally responses to various walking speeds.

• Benefit:• Raise of the forefoot provides an easy

walk with no risk of the forefoot hitting the ground.

• Extension assist spring helps to keep full extension at the terminal swing.

Advantages

• Weight activated hydraulics system is reliable• Knee automatically responds to changes

during gait• Durable• Ability to walk down slopes and stairs• Precise adjustability• Ground clearance

Disadvantages

• Heavier • Require more maintenance• A higher cost.