Lower Limb Prosthetics

Custom-made artificial limbs

Significant advancements have been made in terms of prosthetic components and socket designs for the lower limbs. In particular, lighter and more durable materials have resulted in vast improvements to comfort, function and performance.

The rule of thumb is that the lower the level of amputation, the less expensive the prosthetic and the more capable a patient will be with the aid of a prosthesis. The higher the level of amputation, the higher the number of components required and complexity of system required to achieve a balance between stability and function.

KEY 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. The introduction of plastics, fibreglass and carbon-fibre revolutionised 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 or create a vacuum that can only be released through an expulsion valve fitted to the socket.

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

Knee Joints

Knee mechanisms for Trans-Femoral (above the knee) amputees have 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 reducing the higher expenditure associated with instability.

Foot & 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. Major improvements in design and manufacturing of prosthetic feet have resulted in much more energy efficient and natural walking.

Prosthetic feet can be classified in three groups:

• Energy storing feet store and release the energy that is generated throughout the gait cycle, allowing amputees to walk longer and further. Most users of these feet comment on the “spring” these feet provide.
• Energy dissipating feet allow for forces generated during walking to be 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 are a new generation of prosthetic feet that combine the properties of energy storing feet and energy dissipating feet.

Accessory Components

Some extremely useful accessories are now available, including energy storing and absorbing pylons. These units act like a shock absorber in a car’s suspension. They absorb vertical (up and down) forces and rotational forces. When combined with the appropriate components, these shock absorbers significantly increase walking comfort.

3D printed external fairings that wrap around the lower leg section of a prosthesis create a striking visual effect and can be customised to reflect an amputees personality. This, combined with decorative socket finishing, can provide a truly unique prosthesis.