Prosthetic Knee Joints: Stance Phase Control and Mechanisms

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Questions and Answers

What is the main function of the weight-activated knee brake?

To provide resistance to knee flexion during the stance phase (correct)

To assist with knee extension during the stance phase

To facilitate knee flexion during the swing phase

To act as a free joint during the stance phase

How does the polycentric knee joint work?

Through an instantaneous center of rotation (ICR) mechanism (correct)

Through a weight-activated brake

Through a hydraulic system

Through an external strap

What is an advantage of the hydraulic stance control mechanism?

It provides resistance to knee flexion during the stance phase

It allows for a free joint during the stance phase

It facilitates knee extension during the swing phase

It allows for stumble recovery and adjustable resistance (correct)

What is a limitation of the extension assist mechanism?

It cannot control the speed of the knee joint Signup and view all the answers

What is a characteristic of the polycentric knee joint during the stance phase?

It is very stable Signup and view all the answers

What is a benefit of the hydraulic stance control mechanism?

It allows for stumble recovery and adjustable resistance Signup and view all the answers

What is a characteristic of the weight-activated knee brake?

It provides resistance to knee flexion during the stance phase Signup and view all the answers

What is a limitation of the polycentric knee joint?

It requires proper training to use Signup and view all the answers

What is one of the benefits of the Ottobock 7E9 joint?

Reduction of pelvic tilt Signup and view all the answers

What is a feature of the Ottobock 7E10 joint (Helix 3D)?

Multi-axis joint structure Signup and view all the answers

What does the large flexion angle of the Ottobock 7E10 joint (Helix 3D) facilitate?

Easier accomplishment of activities of daily living Signup and view all the answers

What is a benefit of the integrated expansion swing of the Ottobock 7E10 joint (Helix 3D)?

Easier initiating swing phase Signup and view all the answers

What is a feature of the stance phase control of the Ottobock 7E9 joint?

Dampened, controlled heel strike Signup and view all the answers

What is a benefit of the swing phase control of the Ottobock 7E10 joint (Helix 3D)?

Individual stride-length setting Signup and view all the answers

What is a characteristic of the pylon tube?

Available in different lengths Signup and view all the answers

What is the purpose of the clamp adaptor?

To angle the tube adaptor for the above knee section Signup and view all the answers

What is the primary function of Stance phase control in a knee joint?

To prevent knee flexion during the stance phase Signup and view all the answers

Which type of knee joint mechanism is characterized by a single axis and relies on ground reaction force for knee flexion and extension?

Posterior Offset knee Signup and view all the answers

What is the primary difference between SAKL and HOKL types of Locked Knee mechanisms?

One is automatic and the other is manual Signup and view all the answers

Which type of Swing Phase Control mechanism assists in knee extension during the swing phase?

Extension assist Signup and view all the answers

What is the disadvantage of the Posterior Offset knee mechanism?

It makes it difficult to initiate knee flexion Signup and view all the answers

Which type of Stance Phase Control mechanism works by preventing knee flexion during the loading response phase?

Weight activated knee brake Signup and view all the answers

What is the primary advantage of the Locked Knee mechanism?

It increases knee stability during the stance phase Signup and view all the answers

What is the primary difference between Stance Phase Control and Swing Phase Control?

One is for the stance phase and the other is for the swing phase Signup and view all the answers

Study Notes

Knee Joints

Knee mechanism is divided into Stance phase control and swing phase control.

Stance Phase Control

Types of stance phase control:
- Locked knee
- Posterior offset knee
- Weight activated knee brake
- Polycentric
- Hydraulic

Locked Knee

The knee joint is locked and does not bend during the gait cycle
For K1 patients
Types of locked knee:
- SAKL (Semi automatic knee lock): locks as soon as the patient stands up, and releases when the patient sits down
- HOKL (Hand operated knee lock): user can choose to walk with a free knee if feeling confident

Posterior Offset Knee

A single axis knee
Simple and robust
Depends on the ground reaction force for initiation of knee flexion and extension
Increases knee stability during stance phase, but makes it difficult for initiation of knee flexion
Difficulty in initiation of knee flexion can cause lengthening of the prosthesis, leading to vaulting or circumduction

Weight Activated Knee Brake

Works by preventing knee flexion during loading response phase
Requires a vertical force (body weight) to activate the braking system
When the force is applied, the brake tightens, and there is no knee flexion until 20 degrees of knee flexion
Resistance can be individually adjusted

Polycentric Knee

Works by the ICR (Instantaneous center of rotation) mechanism
When flexion moment is initiated, the ICR moves forward and downward
When the knee is extended, it is very stable during stance phase
When the knee joint is flexed, it acts as a free joint, good for ground clearance
Requires proper training for the patient to use the knee joint

Hydraulic Knee

A liquid is inside the joint, and its resistance can be adjusted individually
Good for stumble recovery, as the flexion resistance can be individually pre-set
Allows going down stairs with foot over foot and going down ramps and slopes
Expensive

Swing Phase Control

Types of swing phase control:
- Extension assist
- Mechanical brakes
- Pneumatic
- Hydraulic
- Electronic

Extension Assist

The assist can be internal or external
Internal: a spring that compresses on knee flexion
External: an external strap that attaches to the knee and stretches on flexion
The speed of the knee joint cannot be controlled
Easy to align and adjust

Hip Joints

Ottobock 7E9 joint:
- Dampened
- Controlled heel strike
- Significant reduction of pelvic tilt
- Smooth and controlled roll-over under full load, providing support of knee joint stance flexion
- Provides a closer approximation to physiological gait

Ottobock 7E10 Joint (Helix 3D)

Multi-axis joint structure produces three-dimensional hip movement to compensate for pelvic rotation and promote a symmetrical, natural gait
Allows for leg-length reduction during swing to help reduce fall risk and increase security
Improves sitting posture and reduces pelvic obliquity to a minimum due to large flexion angle
Large flexion angle makes accomplishing activities of daily living easier
Integrated expansion swings make initiating swing phase easier
Allows for dampened, controlled heel strike in stance phase for a smoother, more controlled roll-over on the prosthesis under full load
Allows for individual stride-length setting to control the pendulum motion during swing phase

Pylon Tube and Clamp Adaptor

Pylon tube:
- Available in different lengths (for pediatrics, BK, AK)
- Available in 2 different diameters (30mm, 34mm)
- Available in 2 different materials (Stainless steel, titanium)
Clamp adaptor:
- Angled tube adaptor for the above knee section

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Description

This quiz covers the different types of stance phase control and swing phase control mechanisms in prosthetic knee joints, including locked knee, posterior offset knee, and more.