Walking is something that lower extremity prosthetic users don’t take for granted. Those first steps on a new prosthesis signal the beginning of a recovery process that is both hopeful and challenging. Today, prosthetic users have an impressive array of feet to choose from… feet and ankles that are made for walking and feet and ankles that are made for dancing, cycling, golfing, swimming, snow skiing, and running. The comfort and flexibility of these dynamic prosthetic feet are helping propel amputees to new levels of activity.

Over the past decade, options in prosthetic feet have expanded from a mere five or six basic styles to more than fifty different models. Gone are the heavy wood, steel and plastic materials of yesterday, replaced by lightweight plastics and carbon fiber composites. Much like the human foot, today’s prosthetic feet are energy returning, actually storing and expending energy to make walking easier and less tiresome. Other key features are toe and heel springs that allow for natural movement of the ankle, shock absorption, multi-axial rotation, adjustable heel heights, and waterproof materials.

So how can you be sure your prosthetist selects just the right foot to fit your lifestyle? Specific Medicare guidelines determine which type of foot is best suited for each user. Several factors are considered such as activity level, rehabilitation potential, occupation, weight, and amputation level.

Under Medicare standards, people with a functional level of 1 qualify for a SACH foot (Solid Ankle Cushioned Heel) or a single-axis foot. Those with a functional level of 2 qualify for a SAFE foot (Solid Ankle Flexible Endoskeleton) or a multi-axial foot. Both of these feet offer cushioning and energy absorption and are virtually maintenance free, however, since they don ’t actually store and release energy, they are not dynamic response. Basic prosthetic feet may be single-axis or multi-axis in their design. Prosthetic feet that function on two or three axes provide increased surface contact for the foot, improving the user’s stability. They are appropriate for functional level 2, but we prefer to use these feet only on a temporary prosthesis and replace them with dynamic feet if possible on the final, definitive prosthesis.

Dynamic-response feet are available to people with a Medicare functional level of 3 or 4. This type of foot is very much like a sophisticated spring that cushions on heel strike, uses the absorbed energy to push the foot forward into mid-stance, and then, into toe-off. The spring action at toe-off propels the prosthesis through the swing phase of the gait and the pattern then repeats. This phenomenon is known as "energy return" meaning that a high percentage of the energy expended when the user steps forward is stored within the foot system, and then returned as momentum for each successive step. The comfort and responsiveness of a dynamic foot can be an important part of enabling a prosthetic user to advance from a minimal activity level to a moderate activity level. People with more active lifestyles require these more responsive feet. They are lightweight and comfortable and usually operate on multiple axes. The result is increased surface contact for the foot which means greater stability and control for the user. While many younger people rely on these feet to propel them through sports and other recreational activities, it’s important for older prosthetic users to realize they too can gain dramatic improvements in mobility.

There are many excellent dynamic-response feet that are well-suited for people with active lifestyles. The Talux from Ossur-Flexfoot features a special keel called the Carbon X Active Keel for maximum energy storage. This foot provides a fluid, natural walking motion on a variety of terrains.

The Ceterus, also from Ossur-Flexfoot, appeals to users who engage in a variety of physical and athletic activities. It has a torsion control cell that reduces rotary forces on the knee and hip joints and shear forces on the residual limb, and a built-in vertical shock pylon that can be adjusted by the user. "In 13 years of trying different feet, this is the best that I’ve ever used," says above-knee amputee Chris Bradley, a prosthetic technician. "I wear my leg 16 hours a day and find I don’t get nearly as tired. It’s really smooth and the natural rotation has helped my golf swing."

Springlite’s Luxon Max is often used on above-knee prostheses that have a computerized knee like Otto Bock’s C-Leg knee. This foot’s split-keel design gives users a smooth impact on heel strike and a natural pivot motion on both the toe and heel. The Luxon Max also has good side-to-side flexion that is especially beneficial on uneven surfaces. "When I got my C-Leg knee, I tried several types of feet and this one felt the most comfortable," says Doug Brooks, COO of Brinker International in Dallas. "I travel a lot and this knee and foot combination lets me move much more quickly and confidently. I also notice that on uneven ground at the golf course I’m more balanced and steadier with the Luxon Max foot."

Springlite’s Luxon Max DP is another good choice. The unique Luxon material is an elastomer that offers superior cushioning, stability and resilience that gives this foot a springy step. It also has a foot plate that separates the heel and forefoot, enhancing flexibility and range of motion. "This foot is flexible, has really smooth rollover, and there’s no dead spot," says Theron Hogue, below- knee user. "It performs great on uneven surfaces so I like to wear it when I’m rock climbing."

For active prosthetic users who frequently struggle with volume loss in the residual limb, we recommend Ohio Willow Wood’s Pathfinder foot combined with Vacuum Assisted Socket System (VASS) technology. VASS creates a vacuum in the socket that has the result of substantially reducing volume loss in the residual limb, leading to a consistent socket fit. The Pathfinder foot is designed for highly active people and features an adjustable pneumatic heel spring and two composite toe springs for great dynamic response.

Dynamic-response feet sometimes include cushioning bumpers at forefoot, mid-stance and heel, and bushings at the ankle to help control alignment. These extra features play an important role in dampening and absorbing shock to the residual limb and help create a more fluid gait pattern. Bumpers and bushings are usually customized by the prosthetist to accommodate each individual’s activity level and body weight. Patients need to remember that feet with multiple moving parts usually require more maintenance, and also tend to have more noise coming from the foot. Because of the need to have access to moving parts for maintenance, it is difficult to design an effective cosmetic covering.

The most specialized prosthetic feet are those created specifically for the high-performance needs of competitive athletes. The Flex-Sprint III is a sprinting foot designed for below-knee users, although it may be suitable for some above-knee users. The Springlite Sprinter is custom made specifically for the serious track and field athlete. It is extremely lightweight with a double contoured toe for high propulsion and decreased drag.

Prosthetic users do a lot more than simply walk on their feet. They engage in a range of activities, many of which require different shoes, and thus different heel heights. Whether it’s cowboy boots, golf shoes, lady’s heels or running shoes, a user-adjustable foot can accommodate them all. Users can quickly change from one shoe style to another, or simply reposition the ankle to accommodate downhill terrain, and then shift it back again for level ground. The Total Concept from Ossur-Flexfoot features a dynamic-response foot with an articulated ankle that adjusts from 10 degrees dorsiflexion to 25 degrees plantarflexion for heel heights from zero up to two inches. Adjustable feet give some users much greater control over their dorisflexion-plantarflexion, which is the up-and-down movement at the ankle that permits the leg to move over the foot during ambulation.

Other specialized designs come from Rampro, manufacturer of the Activankle and the Swimankle. The Activankle is an adjustable, waterproof ankle that is constructed from non-corroding metals. In its unlocked position, the Activankle allows for unlimited dorisflexion with no rotation or lateral movement, a feature that is necessary for jet skiing, snow skiing and rowing. A protective covering keeps sand out of the ankle joint, making it a good choice for users who swim in a beach or lake setting. When the user completes their activity, the ankle is easily locked back into the walking position. The Swimankle is a similar design, but is meant exclusively for swimming, snorkeling and scuba diving. The Swimankle uses the same 70-degree plantar flexion that enables the user to point the foot down, but it does not dorsiflex. It also shifts easily back into a walking position but does not have a protective covering and should not be used in sandy conditions. Maria Greenfield is a bilateral, lower-extremity amputee who enjoys this adaptive design. "When I learned to scuba dive, I got these articulating ankles. I just rotate a little lever at the ankle, and I can point my foot down and put my swim fins on so I can kick and propel myself through the water," she says.

Freedom Innovations has recently debuted its new Ski Foot which clicks directly into a snow ski binding with no boot. According to Ron Harding, a volunteer ski instructor who is also a bilateral, below-knee amputee, using the Ski Foot is "Tremendous…a smooth, fluid motion."

Staying in step with new prosthetic feet and ankles is an important concern for all amputees whether they are athletic, highly active or moderately active. There is a foot that is just right for every user, and knowing what the options are enables you to discuss this issue clearly with your prosthetic provider. Evaluate the pros and cons of different feet and together, you can make the best choice. The correct foot makes walking easier, requires less energy, and increases your comfort and stability. Fortunately, some manufacturers allow a trial period. That means you can actually try out and compare feet before deciding which one is right for you.

Scott Sabolich is the owner and Clinical Director of Scott Sabolich Prosthetics & Research in Oklahoma City, Oklahoma. He is an American Board Certified Prosthetist and state licensed prosthetist. He is a member of the American Association of Orthotics and Prosthetics and the American Academy of Prosthetics. Scott has fit several prestigious athletes including Paralympic medalist Earle Conner (AK) and Roderick Green (BK).

Photo: Maria Greenfield swimleg
Maria Greenfield demonstrates how easy it is to put swim fins with the Swimankle.