There are two basic types of suspension for a below-knee prosthesis: locking pin and
suction. An elevated vacuum system is an optional addition that is used conjunction with
suction suspension.
Importance of Suspension
The suspension or connection of a prosthesis is paramount to a users success and comfort. Poor suspension can result in: a decrease in prosthetic utilization, skin abrasions or blistering, increased pain, poor gait or possible tripping.
A well fitting and suspended socket will keep the patient comfortable through the day.
Suspension Types
The suspension mechanism is determined by the patients goals, conditions, and residual limb presentation. Suspension can be achieved through:
Anatomical suspension- using the anatomy of the patients limb.
Mechanical attachment- using a locking or strapping mechanism that secures the prosthesis in place.
Suction suspension- using a sealing mechanism such as a sleeve or gasket, expelling the air within the socket through a one way valve.
Vacuum suspension- similar to suction suspension but provides a mechanism to increase the negative pressure within the socket with an external vacuum pump.
Advantages & Disadvantages
ANATOMICAL SUSPENSION is advantageous for patients with a limb that permits an anatomical purchase. This may include a bulbous residual limb or unique limb contours that permits a width discrepancy that permits suspension. Generally, these designs do not require the use of gel liners, sleeves, or gaskets. The disadvantages may include challenges for donning the prosthesis, compromised suspension with volumetric changes, or fabrication of the device. The photo to the right uses a "stove piped" pelite liner to provide anatomical suspension.
LOCKING PIN SUSPENSION is advantageous for patients who prefer a simple and secure attachment. The donning and doffing of the device is simplistic, adding socks is relatively simple, and patient preserves range of motion at the proximal joint. Disadvantages include “Pistoning” during swing phase—gravity pulls liner away from limb, decreasing the sense of
connection, and increasing friction. Potential donning challenge for vision impairment or hand dexterity challenges.
SUCTION SUSPENSION is advantageous for patients as it lessens the pistoning affect as the seal is created proximal to the distal end of the limb. This provides the patient the feeling of increased connectivity to the socket during swing phase. The disadvantages can be a bulky sleeve, less range of motion at the proximal joint, compromised suspension with leak.
ELEVATED VACUUM SYSTEM is similar to suction suspension as it eliminates the
movement of the prosthesis on the residual limb. It provides maximum security, limb volume stabilization, increased proprioception, and regulates the air pressure within the socket during both swing and stance phase. Some disadvantages include decrease in range of motion at the knee, possible daily charging and maintenance, may cause injury with improper use or fit, and is expensive for the patient.
The photo the left shows a Willow Wood Limb Logic inline vacuum pump. *Note the delineation of the trimlines of the prosthesis.
For more information, view the video below: