Fluid Friction Dampening Principles

Question 1

For the transfemoral patient capable of walking with a variable cadence:

Answer 1

It is important that the resistance of the knee mechanism respond proportionally to the velocity of the patients gait.

Question 2

Because the gas (air) in pneumatic knee mechanisms is compressible, the compressibility of this gas results in:

Answer 2

A “bouncier” feel for the patient.

Question 3

Fluid for a knee control mechanism must:

Answer 3

• not foam up or create air in the system as this would change the basic property of incompressibility.
• retain constant viscosity
• not be adversely affected by changing temperatures

Question 4

The Reynolds Number is calculated by multiplying the velocity with the diameter of the passageway and the density of the fluid and dividing this product by the absolute viscosity of fluid being forced through the passageway.

Answer 4

True

Question 5

Fluid resistance is ideal for meeting needs of the variable cadence patient because, as increased velocity attempts to force the knee into flexion more rapidly, the knee unit:

Answer 5

• responds with greater resistance flexion.
• engages a second cylinder used for extension resistance and resistance in this direction can be helpful in preventing terminal impact.
• resistance is usually found to be greatest just before the point of maximal knee flexion and just before the point of maximal knee extension, due to the forces placed on the prosthetic knee during gait.
• creates a more smooth and font rolled gait via fluid resistance.