Robotic Prosthetic Limbs


As technology has progressed, so too has our application and usage of technology.  Society has applied technology to everyday uses such as, smart phones, personal GPSs for our cars, even on-line classes.  An equally more important area in which technology has been applied to in recent years has been in the use of prosthetic limbs, or robotic limbs.  But how would you connect a machine to human?  What would be the  ethical as well as technological issues associated with applying humans to technology?  This paper will introduce robotic prosthetics, how they work and their benefits, what types are used, and what developmental hurdles are encountered.  As well as cover any legal, security, ethical, and social issues due to the advancements in robotic prosthetics.

How Robotic Limbs Work and Their Benefits

In 1945 the National Academy of Sciences established the Artificial Limb Program, in order to advance the design and implantation of artificial limbs (Artificial/Prosthetic).  Since then many programs and institutes have been researching and experimenting in order to make prosthetics fully functional, as well as practical in usage.  Modern day prosthetics, or robotic limbs, are defined as mechanical limbs that are controlled by microprocessors and nerve impulses (Resnick, 2010).  There are currently many ways in which the signals from a human nervous system are transmitted to the electronic parts within the prosthetic.

One of the most common forms in which signals are sent from an amputee to the prosthetic is through the use of electromyography sensors (EMG).  When an amputee flexes his muscles the sensors are then translated into the prosthetic (Rewire the Nervous System, 2010).  Another form to transmit signals from the amputee to the prosthetic is known as “targeted reinvention” (Rewire the Nervous System, 2010).  This involves surgery in which the patient’s nerves of another part of his body are rewired to control where the missing limb may be.  Both of these forms  require brain plasticity.  This means that the robotic limbs rely to an extent on a user training a certain movement, i.e. shrugging, to close the hand.  Surgically implementing sensors into the stump of an amputee is also another way to connect the human nervous system to the microprocessors in the prosthetic (Doshi, 2011).  These robotic prosthetics use these different methods of transmission in order to give back some form of former functionality that an amputee lost.

Types and Designs of Robotic Limbs

As with most technology, there are many different designs of robotic limbs.  The company iWalk (using technology developed at MIT) developed the PowerFoot One, a robotic ankle and foot (Bogue, 2005 p. 425).  The PowerFoot One operates by:

Several thousand times each two microprocessors and six sensors evaluate and adjust ankle position, stiffness, damping and power.  Control algorithms generate human like force while traversing ground, slopes, and stairs, providing active amputees with near-normal gait and lower energy expenditure than existing, passive prosthetics. (Bogue, 2005) .

Another example of a lower body robotic limb is Ossur’s Rheo Knee.  The Rheo Knee uses a learning matrix system, or artificial intelligence, to learn an amputee’s walking pattern.  The Rheo Knee is powered by a lithium-ion battery and uses a force sensor and microprocessor to balance the knee (Bogue, 2005).

However, as in the case of feet and knees, robotic hands and arms have also been developed.  Two such cases are Touch Bionic’s iLIMB, and the IOWA.  The iLIMB has “five individually powered digits, each with its own motor” (Bogue, 2005 p. 425).  The IOWA is similarly a five digit maneuverable hand, but instead of using electric motors (which was stated to be used in a later models), to reduce weight, it uses springs and a cable-conduit system (Yang, Abdel-Malek, Potratz, 2005,).  DARPA is currently working on making an arm, the Proto 2 ,which would function as well as a normal arm.  This achieved by attaching the nerves in a patient’s chest to sensors to build an arm that will sense touch, temperature, and vibration (Sofge, 2007).

Hurdles and Developments in Robotic Prosthetics

As with any technology, there are many problems that must be dealt with in order to work properly.  Robotic prosthesis is no exception to the above rule.  The most common problem with prosthetics is economics.    This means that most prosthetics are not economically feasible for the average amputee.  The reasons for this are size variations and the cost to produce the robotic components.  Each prosthetic limb must be custom fitted or adapted to the amputee (Resnick, 2010).  As no human is the exact same height, weight, and proportion to the next, then each one must have measurements taken to asses which modifications need to be made.  Also robotic limbs can range from the high thousands to the millions of dollars; most of them easily costing more than “$100,000” (Resnick, 2010).  Currently new materials are being tested that could more easily be shaped to fit an individuals needs and size (Resnick, 2010).

A more important technological problem is in the sensory itself, or connecting the living nerve’s signals to the machines.  DARPA’s second generation arm, Proto 2, relies heavily on brain plasticity.    Even Proto 2, which has the capacity to sense signals from nerves on the surface, still relies on training the mind to react a certain way in order to manipulate the machine (Sofge, 2008).  A common thought solution to this problem would be for an amputee to be injected with tiny sensors that would then connect to the prosthetic, making communication easier(Sofge, 2007).  However when scientists surgically connected sensors to a patient’s nervous system, the sensors failed within months harming the body’s tissue as well (Doshi, 2011).  But a project led by a group of engineers at Southern Methodist, have found that by shinning infrared light they can stimulate a neuron to send messages.  They also plan to user fiber optic cables, which would allow for faster transmission and possibly let prosthetics “speak” to the brain (Doshi, 2011).

Legal and Security Issues

Whenever humans and technology combine, topics regarding legality and security always come up.  Robotic prosthetics is no exception.  One of the main security, as well as legal, issues going on right now is between current robotic prosthetic users and the TSA.   When an amputee goes through security at an airport he or she is almost always pulled aside for further screening.  “A survey of 7300 amputees conducted by the Amputee Coalition of America in June showed that travelers with limb loss have been subjected to inconsistent, unfair, abusive and often embarrassing screenings by TSA employees” (Trimble 2010).  One of these additional forms of screening is a CastScope, which stated by the TSA website is, “backscatter technology to produce an X-ray image of casts, braces, heavy bandages, and/or prostheses, allowing TSA to quickly and non-invasively identify any potential threats” (Castscope).   The TSA states that this procedure is non-invasive and is required to insure that no harmful devices and/or substances are concealed (Castscope).  However as previously stated many amputees feel that these practices are invasive, embarrassing, and unjust.  They feel that they are being targeted due to their handicap.  The opposite argument states that possible weapons or devices can easily be hidden in robotic limbs and the alternative of learning all the new types of prosthetics isn’t feasible due to the ever advancing technology of artificial limbs.

Ethical and Social Issues

As robotic limbs become more functional and capable, the question arises when they may give an amputee an unfair advantage.  This question is what originally barred Oscar Pistorius from trying out in track and field for the 2008 Summer Olympics.  Oscar Pistorius is a double amputee, who in 2007 sought to try out for the national track team.  However the International Association of Athletics Federations (IAAF) ruled that his prosthetic limbs gave him an unfair advantage (Oscar, 2008).  The report issued stated that Oscar Pistorius’s limbs return three times as much energy than a normal limb, and that they have twenty-five percent less expenditure than normal limbs (Oscar, 2008).  Therefore giving Oscar Pistorius a clear advantage over the other runners.

Oscar Pistorius soon after filed an appeal with the Court of Arbitration for Sports (CAS) to appeal the decision.  A report made by many renowned doctors and developers of robotic limbs convinced the CAS to over turn the decision.  The report showed that when you consider the disadvantages as well as the advantages of prosthetics limbs, “lower-limb sprinting prostheses appears to be physiologically similar, but mechanically different than running with intact limbs” (Bundle, 2009).  Even thought this report proved that prosthetics limbs gave Oscar Pistorius no clear advantage, it still raised the question.  When will artificial limbs give individuals an unfair advantage?


By using microprocessors, with different types of sensors, as well as algorithms, we can build robotic parts that attach and even combine to an amputee.  The progress and development of prosthetic limbs have been massive within the past ten years.  Even though there are many developmental problems with robotic prosthetics, scientists and doctors are continually experimenting and building to create the next and better prosthetic.  But as with any progression in technology there will always be concerns to how these progressions will effect and define society.   Regardless of these concerns, modern prosthetics  show us that technology has progressed to such a point that we can now combine robotic parts to humans to replace those originally lost, at near fully functional levels.