Prosthetics: A Design for Human Variability

Adaptive technology is any object or system that is specifically designed for the purpose of increasing or maintaining the capabilities of people with disabilities. Prosthetic limbs are a fine example of such an adaptive technology. While rare, limb amputations have become increasingly common worldwide. Often times, this kind of amputation leaves the victim with the inability to perform necessary daily tasks due to reduced functionality. In an effort to recover the lost functionality, a prosthetic limb can be fitted to the person. Until recently, the benefits from such prosthetics were often outweighed by the burden of their use or  attachment to the body. However, new prosthetic limbs have been developed which dramatically increased functionality and in some cases actually overtake the utility of biological limbs. These prosthetics have allowed users to live a productive and normal lifestyle free from limitations. In fact, specialized prosthetics have even been made to allow patients to participate in sports and recreation.

pistorius-feature-525The “Cheetah Leg” is optimized for sprinting. The prosthetic is built from carbon fiber and can boast a high strength at about half the weight of a biological leg. The decreased weight requires less torque to swing forward. This allows for faster rotation with less exertion. The shape of the leg acts as a spring, which stores energy on the heel strike and releases it at the toe-off. The length of the prosthetic also increases the stride of the runner in relation to their height. Overall, the performance of the limb is remarkable for a prosthetic and may even surpass that of a normal leg. In fact, the Cheetah Leg has become a topic of debate in the Olympics due to its possible advantage.

flipperFor marine situations, a promising prototype is the “Neptune” flipper. The Neptune is configurable for above and below the knee amputations. The purpose of the Neptune is for balancing the power of the leg kicks of uni-lateral amputations. Also, for bi-lateral amputations, two Neptune flippers could be used to add power to the swim stroke. Since the majority of amputations are due to health conditions, the flipper could allow users to exercise after their surgery. The initiation of a health routine could prevent further limb amputations, and improve the health of the patient.

KONICA MINOLTA DIGITAL CAMERAProsthetics have also been developed for winter sports. Although a walking-limb can be modified and used, a ski-specific alignment should be performed for the duration of the activity. Additional foot dorsiflexion and external knee support should be added. For advanced users specialty feet, which eliminate the boot, are available. The plantar surface of the ski foot can be modeled after the boot sole and attached directly to the ski bindings eliminating the boot altogether. This eliminates excess weight, but, more importantly, enhances energy transfer to the sporting equipment for more efficient performance. Individuals with uni-lateral amputations will usually opt to use a single ski with modified bi-lateral forearm outriggers. Recently, a  prosthetic has been designed specifically for sports that require a loaded, flexed knee position, such as snowboarding. Snowboarders are in bi-lateral dynamic hip, knee and ankle flexion as they negotiate the hill. This new knee is adjustable and produces the weighted knee flexion needed to snowboard successfully. No additional adaptive gear is necessary when using the energy-storing knee.

Recent research efforts have propelled protheses design from century-old devices that were uncomfortable to wear to technically advanced devices. The functionality of the new devices is approaching that of the original limb and, in some instances, surpassing it. These prosthetics have given patients the opportunity to perform daily functions and live a normal lifestyle not limited by the functionality of their prosthetic. Prosthetic limbs are a model example of an adaptive technology.

13 thoughts on “Prosthetics: A Design for Human Variability

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  4. Hi,

    My 84-year-old mom has just this year overcome years of total deafness and a host of other problems. (Her vitals are all still good, and since her hearing has been substantially restored, her cognition has improved by leaps and bounds, which is very encouraging; really, all her problems, even cognitive ones now virtually nonexistent, have been of a peripheral and circumstantial nature; yet together, they have been quite life-limiting. Anyway, these problems are finally fixed.) I am writing you now because there persists one stubborn issue that seems to defy all normative remedies: Serious joint damage from injuries she incurred in middle age, especially in one ankle and one knee (all cartilage gone from the latter, with bone noisily grinding away on bone; too late to replace this knee, as she did the other one 11 years ago. The arms also have joint damage, so that offloading more of the work from the legs to the arms is not practical). Mom’s mobility problem is preventing her from having the normal life of a healthy 84-year-old, and is causing a host of spin-off problems, e.g.: (1) a sporadic lack of alertness from inactivity (Note, _not_ due to dementia, though it could eventually lead there if not dealt with); (2) a tendency not to get to the bathroom in time (She is wearing adult pull-ups to help mitigate this, but wetting herself is adding to hygiene and discouragement problems); and (3) a recurring sore spot and yeast problem (both needing constant monitoring & assistance from me, her 53-year-old son).

    Mom is mentally alert & could have years more of productive life, if only we could find some kind of robust external support to compensate for the ankle & especially the knee (certainly more than just a hinged knee brace). She needs to lose weight (5’1″, 186 lbs.), but being stuck in a chair most of the time (walker to get to the bathroom — that is, when she doesn’t need to be wheeled there; wheelchair for her infrequent trips out…) is making any form of exercise, or even just regular movement, fresh air, etc. very hard to get. _We_are_really_desperate_ to find creative solutions to her problem. →Do you know of any experimental external support/mobility devices that might be able to help her walk again? My fantasy solution would be to find a team of robotics students to spec out & build a kind of high-tech set of glorified “crutches” — external robotic legs that would walk her places (etc.) while supporting her at the underarms, as I do now at times — Being 6’2″ and reasonably strong, if I’m careful to stand in close in front of her so as not to injure my temperamental back, I can, by lifting her at the underarms (or depending on the task at hand, by drawing her upward by the hands, arms outstretched), enable her to stand up, sit down, walk, go up & down steps, & get up into & down out of the minivan I drive her around in.

    Mom is not a wounded vet, but she’s still a worthy subject for someone, perhaps engineering students, who would be willing to take up the challenge. I am certain the building blocks already exist, are even becoming commonplace, for the mechanical mimicking of the support functions I am currently performing. I do not mind helping Mom in this fashion, but if she had an extra (external) pair of robotic legs/crutches that could do essentially what I do (with her at the controls instead of me), I know she could feel less utterly dependent on others, and this would do worlds of good for her. I very strongly believe that it would extend and enrich her life.

    We are located in southwest Washington State, nearly equal distances from Seattle, WA and Portland, Oregon, but I will take her anywhere people are willing to try & help her. I hope you’re still out there, because time’s a-wasting for my mom, who’s just one creative solution away from having her life back in a substantial fashion, and not having to feel all the time like she’s a helpless burden and as if it’s basically all over for her. Who will answer the call and help my mom? I’m sure it will make a worthwhile school project for qualified students, and in a very real way will save the life of a worthy person who has much left to give.

    (We are certainly open to other solutions, though please bear in mind that most common therapies have already been ruled out. Also, the robotic legs/crutches idea seems like a very natural one to me, as I am actually already acting as such a mechanical walker for her. All she needs is a device that will do what I do that is always available to her and for which she can operate the controls, herself.)

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