Prosthetics Knee Unit


Selecting the appropriate prosthetic knee unit for the transfemoral amputee (above knee) is important to achieve a successful outcome and should be based on the person’s activity level, lifestyle and general health. The latest advanced knee is not necessarily the best choice for everyone. Safety and stability for some amputees are more important than functional performance. More active amputees prefer a knee that will give them a higher level of function even if it requires greater control.

There are seven different types of knee units

Mechanical Hydraulic Knee
These systems are a liquid medium (usually silicone oil) instead of air to respond to a wide range of walking speeds. For active patients, this unit will provide the closest thing to normal knee function. The hydraulic knees provide a smoother gait.
Single Axis Knee
A simple hinge hinge that allows the prosthetic shin to move freely in flexion and extension. This unit is primarily for patients with long residual limbs who are able to volantarily stabalize the knee through active hip extension against the posterior wall of the prosthetic socket.


Polycentric Knee
Referred to as “fourbar” knees. More complex in design with the knee is that the leg’s overall length shortens when a step is initiated, reducing the risk of stumbling. These knees are suitable for a wide range of amputees e.g. when they have difficulty in walking with other knees, have knee disarticulation or bilateral leg amputations, or have long residual limbs.

Weight-Activated Stance Control Knee
A very stable knee often prescribed for a first prosthesis. When weight is placed on the prosthesis, the knee will not until the weight is displaced. This knee is also prescribed for older or less active patients.


Pneumatic Knee
These knees consist of pistons inside cylinders which contain air. Pneumatic control compresses air as the knee is flexed, stores the energy and then returns the energy as the knee extends.
Manual Locking Knee
Incorporates an automatic lock that can be unlocked voluntarily. Walking is possible with the lock either engaged or disengaged. The locked knee
requires excessive energy to use and produces a stiff gait, but is the most stable knee available.


Microprocessor knee
A more natural gait is the result of using these knees because the amputees lower the amount of effort they use to control their timing. They are however, heavier, the initial cost is higher and they require more maintenance. Onboard sensors detect movement and timing and adjust the fluid or air cylinder accordingly.