Specialty Lower-Limb Prostheses – Special-Purpose Prosthetic Legs Enhance Life For Amputees
07 Feb 2017
Here’s a question: Name an activity of daily living that is particularly risky for a lower-limb amputee.
If you are in fact an amputee or an amputee’s caregiver, you probably can come up with a lengthy list of answers to that question…among them most likely being “Taking a shower.”
Think about it from the amputee’s standpoint: You don’t want your expensive prosthetic leg to get wet, so you take it off and maneuver yourself into the shower, usually shifting your weight onto a shower stool positioned on an uneven surface. When finished, you repeat the procedure to exit, now coping with the added hindrance of a wet floor… a fall just waiting to happen! And even if you have configured your home bathroom to facilitate your entry and egress from your own shower enclosure, what do you do when you travel?
One answer is a shower leg, a simplified prosthesis designed to withstand water and thus be worn in the shower, so the amputee can stand on both legs with both hands free. The shower leg is one of various prosthetic leg designs amputees can access for specific activities. Some, like running legs, swim legs and ski legs, are designed for amputees engaged in vigorous activities, while others can make life better for most patients who can tolerate an artificial limb.
Given enough time and use, the components in a prosthetic limb will encounter some type of operational malfunction or wear out altogether. As a spare tire greatly lessens a driver’s travail when a blowout occurs, a backup prosthesis will enable amputees to maintain a reasonable level of mobility while the primary system is repaired, upgraded or replaced.
Unfortunately, few funding agencies accept the need for a secondary functional leg, but the good news is that the stand-in prosthesis can be relatively simple in assembly, constructed of parts from an older or temporary limb, and held in reserve until needed.
A common approach is to maintain a previously used prosthesis in a reasonable state of repair to be available for short-term stand-in duty should the primary limb go down.
In addition to its standby role, a backup prosthesis can be worn for specific pursuits such as yard work and other outdoor activities that could damage the more-sophisticated and expensive componentry in the primary limb.
The key characteristic of a shower leg, as well as a swim or dive leg, is that its various parts must be waterproof or at least water-resistant. This requirement eliminates the majority of feet, knees and other components incorporating moving parts, bumpers and mechanical joints… all likely to rust or deteriorate with water contact.
Like a backup prosthesis, a shower leg can be of relatively simple construction, perhaps including parts from a previous limb.
The “foot” can be an actual anatomical prosthetic foot that won’t deteriorate if immersed in water – two examples are the SAFE II waterproof foot and Seattle Lightfoot – or a potentially more stable “peg leg” platform such as the Terra-Round Foot. The Terra-Round is waterproof, flexes to accommodate uneven terrain, such as a sloping shower floor, and incorporates a traction base pad to protect against slips. If an anatomically shaped foot is used, a tread pattern can be melted into the plantar surface for better traction.
A good shower leg not only gives the wearer added safety when entering or leaving a tub or shower enclosure but, by obviating the need to hang onto a railing for stability, also frees both hands for the task at hand – no more one-handed shampoos!
The same basic requirements for a shower limb also pertain to prostheses for amputees who like to swim, water ski or explore underwater. In addition, a swim/dive prosthesis should be designed to protect components from corrosive beach sand and salt water, provide good suspension in the water, and maintain reasonably neutral buoyancy so the limb does not seek to float while the wearer is diving or walking in the water. Some designs allow the leg to fill with water on immersion and drain when out of the water.
Various specialty components can be designed into a swim/dive limb. Swim foot/ankle units enable wearers to walk to the water, then can be repositioned to a high degree of plantar flexion for swimming. A knee unit designed specifically to allow transfemoral amputees to enjoy water activities also is available.
A swim prosthesis allows unilateral amputees to move through the water with legs of approximately the same length, thereby relieving the need to compensate for lack of kick on the amputated side. Adding a flipper enhances swim velocity and reduces energy expenditure.
For scuba diving, a swim/dive leg also reduces air utilization, enabling the wearer to remain submerged longer. Because scuba diving subjects the limb to greater water pressures, a second suspension sleeve covering the residual limb and top of the prosthetic socket helps maintain the watertight seal for the socket interior.
One other strategy for prosthesis wear in or near the water bears mention. A waterproof cast or bandage protector placed over the entire limb and evacuated with a self-contained vacuum pump can keep the prosthetic leg or arm completely dry for light short-term water activities. These covers are not intended for repeated use.
Running limbs have received considerable public attention in recent years due to major assembly improvements and the accomplishments of amputee sprinters, notably South African Oscar Pistorius who for a time was a strong possibility to compete in the Beijing Olympics. (As it was, Pistorius won gold medals at the subsequent Beijing Paralympics in the 100 meters, 200 meters and 400 meters, including a world record in the 400.)
These technologically advanced limbs must be able to withstand the incredible impact force relayed from the ground to the runner’s residual limb with each step and at the same time protect the residual limb from that same impact shock.
Skin breakdown resulting from shear forces encountered in running is common among amputee athletes.
For recreational walkers and slow joggers, impact shock absorption can be achieved with a deforming dynamic response heel and plantar flexion bumper built into the prosthetic foot. However, studies have shown that a dynamic response heel has minimal effect at higher speeds, thus running legs for serious athletes frequently do not incorporate a heel at all but achieve energy storage and release with a high-strength flexible shin-foot that absorbs impact forces through mid-stance then return that energy to propel the limb forward through toe-off.
Various prosthetic manufacturers now offer blade-type running feet in different configurations for runners of different weights and body sizes.
Other Specialty Limbs
Modern prosthetic componentry is enabling many amputees to readily participate in vigorous outdoor activities. Often a particular product can be incorporated into, or temporarily added to, the amputee’s basic prosthesis to facilitate such participation.
Golf Prostheses – One good example is the addition of a torque absorber to the limb to allow internal and external rotation between the socket and foot during a golf swing. Casual amputee golfers do not normally require a special limb to enjoy the game; however, incorporating a torque unit with friction adjustment into the primary limb can significantly enhance a golfer’s ability to control swing and follow-through. Good socket cushioning is also essential for golfers intending to play 18 holes, so a beefed-up insert or liner can be another valuable addition.
Skiing Legs – Downhill or cross-country skiing is well within the realm of many healthy amputees. Specialty feet modeled after the sole of a ski boot can be added to an “everyday” limb to facilitate attachment directly to the ski binding, eliminating the need for a boot altogether.
Rock Climbing – Standard prosthetic feet are not stressed for rock-climbing because the toe is not sufficiently rigid to support the amputee’s full body weight when only that portion of the foot is in contact with the rock face. High-strength specialty feet for this activity are designed to provide that stability and are shaped to fit into tight places frequently encountered in this activity.
For active amputees using specialty prosthetic feet for different activities, a quick-release fitting such as the Ferrier Coupler can be a real time and money saver.
These devices enable different lower components to be used with the same socket without rigorous disassembly and reattachment. They are also helpful for temporary removal of the prosthesis for specific motions or activities, such as…
• clearing the raised lower door frame when exiting an automobile,
• sitting more comfortably for prolonged periods,
• removing the prosthetic foot for swimming,
• attaching a shower foot, and
• adding a temporary foot while the primary one is being repaired.
Optimizing prosthetic legs for specific activities is becoming increasingly common these days as our practitioners seek to further expand quality of life, safety, and fitness opportunities for our patients. To discuss possibilities for a specific individual or amputees in general, we invite you to call our office.