A good prosthetic foot should be strong, as it will be taking on huge force and torque as the user walks and runs. Feet must also be small enough to fit within a foot shell, a cosmetic covering for the prosthetic foot, and thus fit within a shoe. Being light, strong, and small, and yet functional and durable is the challenge. Early designs for prosthetic feet were often a solid piece of wood. A similar design, the SACH (solid-ankle-cushioned-heel) is still in use because of its sturdy function, especially useful for individuals with lower activity levels. A SACH foot typically has a rigid inner structure (wood or plastic) surrounded by a compressible foam cosmetic shell.
Today’s more sophisticated feet, which add more functions, are secured inside a cosmetic shell. Most people never see their prosthetic foot without this exterior shell. The cosmetic shell, which stretches around the foot prosthesis and is held in place and serves the purpose of making the prosthesis look like with an anatomical foot and it also fills the space in the shoe.
Prosthetic feet are designed to meet the needs that fit the lifestyle and activity level of the users. Here are some factors to consider.
Materials: The materials in a prosthetic foot differ by activity level/ mobility class. Wood, plastic and foam are usually found in feet designed for individuals who have low activity levels and require stability. Carbon fiber feet meet the functional needs for shock absorption and energy efficiency, and are lightweight as well.
Comfort: A prosthetic foot has to feel good and to meet all the activity goals. Comfort allows the user to be more active, and the function of the prosthetic foot directly affects comfort.
Function: Prosthetic feet must act as a shock absorber as they strike their heel to the ground, adapt to uneven terrain, provide a smooth rollover from heel to toe, and provide a rigid lever for propelling forward when they finish their step (“toe-off”).
Multi-axial motion: Some prosthetic feet are designed to mimic the ankle, which allows the foot to move in multiple planes. Multi-axial motion is needed to walk comfortably and confidently on uneven ground, when your foot must adapt to whatever it encounters.
Energy storage: A foot made with carbon fiber for energy storage acts as a spring, compressing as you apply weight and propelling you forward as your foot rolls, returning energy to your step as the spring releases.
Body weight: Prosthetic feet are designed for a specific weight range. To ensure that a prosthetic foot performs well for the user, choose the one suited to their body weight class.
Clearance: When the user stands, a prosthesis fills the space between the residual limb and the floor. It is designed to add only the length needed to equate or balance the other leg. Most prosthetic feet are 2 to 7 inches in height. Consequently, a limb loss near the ankle may limit some options to low-profile prosthetic feet.
Preferred Foot shell and the Colours: Shells can be ordered in colors to match the skin tone, in a range of sizes and often with a split toe for wearing sandals. Low-end shells may lack detail, such as toes, and may be attached to the prosthetic foot. At the high end, the toes and skin colors are more realistic. If the activity level is 3 or 4, one needs to look for a foot with a shell that can be replaced once it’s worn out completely due to high end, impact levels and usage.
Price: The price of prosthetic feet generally rises with the activity level because additional functionality translates to more structure and more expensive materials. Before making a final selection, make sure the prosthetic foot of choice will enable the end user to increase or maintain their activity level, work a longer day and lead an active and dynamic life.