Over the past decade, no class of prosthetic componentry has shown greater advancement than foot and ankle systems. Today’s components reflect improved engineering, lightweight materials and versatile designs, producing enhanced biomechanical benefits and a more natural gait for amputees.
The closer a selected foot-ankle system matches the abilities, environment and activity desires of the amputee, the better the outcome. That’s where our experienced prosthetic staff makes a major difference.
The first step is to determine the appropriate degree of prosthesis complexity and performance based on the patient’s physical condition and capabilities. While the selection of prosthetic feet has grown, amputees may be limited in their access to many of them by the extent to which those designs are deemed reimbursable under Medicare and private insurance.
Medicare uses a system of “functional levels” to define medical necessity for different degrees of sophistication of prosthetic devices. A new amputee’s predicted functional level is generally determined by the referring physician and prosthetist, taking into account the patient’s (1) history; (2) current status, including condition of the residual limb; and (3) desire to ambulate.
Though new designs typically tend to the high end of performance – and cost – more choices are becoming available and increasingly affordable for the lower functional levels. Moreover, new features are making some foot options appropriate for more than one level.
K1 — Low-Level Function (Household Ambulator)
Amputees in this category have the ability or potential to use a prosthesis for transfers on level surfaces at a fixed cadence and tend to be older patients who have undergone an amputation due to vascular insufficiency. They generally require safe, basic function and lightweight for moving relatively short distances.
The SACH (solid ankle, cushion heel) foot is the basic prosthetic unit for the K1 patient. The SACH foot simulates plantar flexion at heel strike by compression of an elastic heel wedge and provides forefoot dorsiflexion by means of a flexible toe section. The SACH foot’s simple construction (no moving parts), lightweight, and low cost make it an ideal choice for preparatory (training) prostheses.
The single-axis foot incorporates the enhancement of an ankle component. This mechanism allows the forefoot to move downward through forward action at the ankle, rather than through initial heel strike. Movements are modulated by plantar flexion and dorsiflexion bumpers. This is also a low-cost, lightweight option, though somewhat more expensive than SACH models. Some single-axis models incorporate dynamic response characteristics appropriate for as high as K3 use. Because single-axis feet increase knee stability in early stance phase, they are often preferred for above-knee amputation levels.
K2 and K3—Mid-level Function (Community Ambulator)
Amputees in the K2 classification have the ability or potential for ambulation on uneven surfaces and to navigate curbs and stairs. K3 patients can be bexpected to navigate inclines and higher barriers and to sustain their activity over time, as in those who maintain employment or engage in sports such as golf or walking programs.
Patients in this group can benefit from more durable SACH foot models, certain multiaxial designs, and feet incorporating dynamic response characteristics. Compared to a SACH model, dynamic response feet provide increased range of motion, decrease impact loading on the contralateral sound foot, and may reduce energy expenditure in ambulation. The newer designs often offer a flexible keel foot as part of the system to provide dynamic assist at toe-off, helping propel the leg into swing phase. Here are some notable examples:
- The Össur Elation Flex-Foot incorporates a carbon fiber keel in its design with the added feature of button-powered heel-height adjuster to allow patients to use shoes of differing heel heights appropriate for formal or informal wear. While Össur’s Flex-Foot series is typically associated with high-tech and high performance, its Sure-Flex foot is appropriate for K2 patients in both cost and performance.
- The long-popular Seattle Lightfoot is now also available as the LightFoot2, incorporating an improved keel providing enhanced rollover.
- Otto Bock’s Springlite II is a proven lightweight energy storing foot adaptable to a wide range of patient weight, heel height and foot size requirements.
- Freedom Innovations, a new manufacturer on the scene, offers two innovative feet in its Revolution series: the Runway, featuring a user adjustable heel height, and the Renegade, an extremely lightweight foot with built-in shock-absorbing qualities.
Multiaxial ankles are well-suited to K2 and K3 function in that they accommodate uneven terrain by providing inversion-eversion and some degree of transverse rotation in addition to dorsiflexion and plantar flexion. The multiaxial mechanism may be a distinct component mated to a separate prosthetic foot; examples include the Seattle C-stance ankle combined with a Seattle Lightfoot and the College Park Endo IP ankle used with a TruStep foot. Alternatively, the ankle mechanism can be made an integral part of the foot component, as with the K2 Sensation and College Park Tribute.
Multiaxial ankle/foot systems are particularly appreciated by amputees who enjoy outdoor activities, notably hikers and golfers. They also lend themselves well to the needs of bilateral amputees. These patients frequently benefit from a dynamic response foot built around a flexible keel, which deforms during weight-bearing, storing energy, then releases that energy during late-stance phase, providing forward propulsion.
Foot-ankle systems for these levels now reflect many of the design advantages previously developed for the very active, high-impact level 4 patient. Steady improvements in weight reduction and reliability have brought K3-K4 components within the realm of moderately active amputees. For example, lightweight carbon fiber materials, energy-storing and shock-absorbing heels, and split-toe features are now available in various newer products. Other leading dynamic response feet suitable to the K2-K3 categories now available include:
- Össur Ceterus Vari-Flex (formerly the Flex-Walk) and Talux
- Otto Bock C-Walk
- Endolite Dynamic Response Foot (with Multiflex Ankle), and
- Ohio Willow Wood Impulse (can be mated with the Earthwalk ankle).
K3-K4—Upper-Level Function (High-activity, Athletes)
The K4 applications are typically high tech, high impact and high cost. A relatively small percentage of all amputees will qualify for reimbursement of ankle-foot components in this category.
Though formerly largely the domain of athlete-amputees and active children, these systems reflect the expectation that some middle-aged amputees may be increasingly inclined to remain an active participant in golfing, hiking, shopping and gardening.
Devices appropriate for K4 and some higher level K3 amputees exhibit high performance spring like qualities and shock absorption capabilities. Examples of devices in this range include:
- Össur Ceterus and Re-Flex VSP
- Otto Bock LuXon Journey, and LuXon Max DP, and
- Ohio Willow Wood Impulse, Carbon Copy 2 and Pathfinder.
The College Park TruStep, a pioneering system appropriate for highly active amputees, features a fully articulated foot, split-toe design and dynamic response. College Park’s Venture offers a new feature, patient-adjustable stride control, for adjusting the foot’s gait characteristics to reflect changing activities, as from home or office use to a hiking trail or gym.
Though this discussion has highlighted many of the leading ankle-foot components available to the lower-limb amputee population, there are in fact many more, all of which offer some special benefit to particular amputees.
Our role is to determine and provide the most appropriate componentry for patients entrusted to our care.
We welcome your inquiries about any of the components discussed in this article and will be pleased to work with you to devise the best solutions to amputee prosthetic needs.
Foot prosthetic technology has come a long way. Please call LeTourneau Prosthetics today for your free consultation. We have offices located in Beaumont, Nederland and Jasper, Texas.