Lower Extremity Prosthetics

Prosthetic limbs are custom designed and custom made for each amputee.
Over the past couple of decades significant advancements have been made in terms of prosthetic components and socket design. The use of lighter and more durable materials has resulted in improved comfort and function.

The socket design and the components determine the level of comfort and function we can expect from a prosthesis.

We will briefly overview the components of lower extremity prostheses:

SOCKET AND INTERFACE

The purpose of the prosthetic socket is to transmit forces from the residual limb to the prosthesis. A well constructed socket will provide comfort and stability during walking and standing on a prosthesis. Traditionally, sockets were made out of materials that were available as natural resources. Wood, metal and leather were predominantly used until the 1960's. The introduction of plastics, fibre-glass and carbon-fibre revolutionized socket manufacturing and design, making them lighter and much more durable.

The interface/liner is intended to absorb shock and shear forces on the residual limb. It fits between the residual limb and the socket and can be made from various soft materials. Modern interfaces are constructed from silicon and urethane polymers, which help protect the tissue. They can also assist with suspension of the prosthesis by incorporating a pin that connects to a locking mechanism in the socket.

Combining these new technologies with new socket designs, such as Total Surface Bearing (TSB) or Ischial Containment (IC), have also improved prosthetic comfort and function dramatically.

FOOT AND ANKLE

The human foot and ankle is a very complex functional unit. It provides stability as well as flexibility, absorbs forces and generates energy for efficient and comfortable walking.

As each patient has different needs and lifestyles, it is vital to select the most appropriate prosthetic foot to achieve maximum comfort and function. Over the past decades we have witnessed major improvements in design and manufacturing of prosthetic feet, allowing much more energy efficient and natural walking.

· Energy storing feet

Energy storing feet store and release the energy that is generated throughout the gait cycle. It results in a more energy efficient gait by reducing energy consumption, allowing amputees to walk longer and further. Most users of these feet comment on the "spring" these feet provide.

· Energy dissipating feet

Forces generated during walking are absorbed and redirected, allowing very little energy to be transferred to the residual limb. Combining different materials also allows those feet to conform to walking surfaces, providing the amputee with more stability and comfort.

· Hybrid feet

In the last few years further improvements in manufacturing technology have delivered new developments that combine the properties of energy storing feet and energy dissipating feet. This results in compliance and energy return.

KNEE JOINTS

Knee mechanisms for trans-femoral (above-knee) amputees have also seen major technological advancement in the last decade, greatly improving safety and function. Microprocessor controlled knee units have led these advances.
Incorporation of hydraulic and pneumatic mechanisms allows modern knee units to adapt to variable cadence and assists walking on slopes and stairs. New design concepts for multi-axial knee units have seen increased stability without the accompanying instability downside of higher energy expenditure.

ACCESORY COMPONENTS

Some extremely useful accessories have also been designed recently. Perhaps the most interesting is the group of energy storing and absorbing pylons. The intention of these pylons is to decrease the level of force transmitted through the prosthesis at heel strike. These units act like a shock absorber in a car's suspension. They absorb vertical (up & down) forces and rotational forces. When combined with the appropriate components, these shock absorbers increase walking comfort significantly.