In medicine, a prosthesis, (from Ancient Greek prósthesis, "addition, application, attachment") is an artificial device that replaces a missing body part lost through trauma, disease, or congenital conditions.
The main types of prosthesis, craniofacial and somato (body), can be divided further by anatomical region. Craniofacial prostheses include intra-oral and extra-oral prostheses. Extra-oral prostheses are further divided into hemifacial, auricular (ear), nasal, orbital and ocular. Intra-oral prostheses include dental prostheses such as dentures, obturators, and dental implants. Somato prostheses include breast and limb prostheses. Breast prostheses include full breast devices and nipple prostheses. Limb Prostheses include upper extremity and lower extremity prostheses. Upper extremity prostheses are used at varying levels of amputation: shoulder disarticulation, transhumeral, elbow disarticulation, transradial, wrist disarticulation, full hand, partial hand, finger, partial finger. Lower extremity prostheses are also used at varying levels of amputation. These include hip disarticulation, transfemoral, knee disarticulation, transtibial, symes, foot, partial foot, and toe. The type of prostheses needed will be designed and assembled according to the patient's appearance and functional needs. For instance, a patient may need a transradial prosthesis, but need to choose between an aesthetic functional device, a myoelectric device, a body-powered device, or an activity specific device. Depending on the patient's funding situation, she may have the option to choose more than one device.
A transhumeral prosthesis is an artificial limb that replaces an arm missing above the elbow. Transhumeral amputees experience some of the same problems as transfemoral amputees, due to the similar complexities associated with the movement of the elbow. This makes mimicking the correct motion with an artificial limb very difficult. In the prosthetic industry a trans-humeral prosthesis is often referred to as a "AE" or above the elbow prothesis.
A transradial prosthesis is an artificial limb that replaces an arm missing below the elbow. Two main types of prosthetics are available. Cable operated limbs work by attaching a harness and cable around the opposite shoulder of the damaged arm. The other form of prosthetics available are myoelectric arms. These work by sensing, via electrodes, when the muscles in the upper arm moves, causing an artificial hand to open or close. In the prosthetic industry a trans-radial prosthetic arm is often referred to as a "BE" or below elbow prosthesis.
A transfemoral prosthesis is an artificial limb that replaces a leg missing above the knee. Transfemoral amputees can have a very difficult time regaining normal movement. In general, a transfemoral amputee must use approximately 80% more energy to walk than a person with two whole legs. This is due to the complexities in movement associated with the knee. In newer and more improved designs, hydraulics, carbon fiber, mechanical linkages, motors, computer microprocessors, and innovative combinations of these technologies are employed to give more control to the user. In the prosthetic industry a trans-femoral prosthetic leg is often referred to as an "AK" or above the knee prosthesis.
A transtibial prosthesis is an artificial limb that replaces a leg missing below the knee. Transtibial amputees are usually able to regain normal movement more readily than someone with a transfemoral amputation, due in large part to retaining the knee, which allows for easier movement. Lower extremity prosthetics describes artificially replaced limbs located at the hip level or lower. The two main subcategories of lower extremity prosthetic devices are 1.trans-tibial (any amputation transecting the tibia bone or a congenital anomaly resulting in a tibial deficiency) and 2.trans-femoral (any amputation transecting the femur bone or a congenital anomaly resulting in a femoral deficiency). In the prosthetic industry a trans-tibial prosthetic leg is often referred to as a "BK" or below the knee prosthesis while the trans-femoral prosthetic leg is often referred to as an "AK" or above the knee prosthesis.
Prosthetics have been mentioned throughout history. The earliest recorded mention is the warrior queen Vishpala in the Rigveda. The Egyptians were early pioneers of the idea, as shown by the wooden toe found on a body from the New Kingdom. Roman bronze crowns have also been found, but their use could have been more aesthetic than medical.
Another early mention of a prosthetic comes from the Greek historian Herodotus, who tells the story of Hegesistratus, a Greek diviner who cut off his own foot to escape his Spartan captors and replaced it with a wooden one. Pliny the Elder also recorded that a Roman general who had his arm cut off had an iron one made to hold his shield up when he returned to battle. A famous and quite refined historical prosthetic arm was that of Götz von Berlichingen, made at the beginning of the 16th century.
Around the same time, François de la Noue is also reported to have had an iron hand, as is, in the 1600s century, René-Robert Cavalier de la Salle. During the Dark Ages, prosthetics remained quite basic in form. Debilitated knights would be fitted with prosthetics so they could hold up a shield. Only the wealthy could afford anything that would assist in daily life. During the Renaissance, prosthetics developed with the use of iron, steel, copper, and wood. Functional prosthetics began to make an appearance in the 1500s.
Götz von Berlichingen, a German mercenary, developed a pair of iron hands that could be moved by a series of catches and springs. An Italian surgeon recorded the existence of an amputee who had an arm that allowed him to remove his hat, open his purse, and sign his name. Improvement in amputation surgery and prosthetic design came at the hands of Ambroise Paré. Among his inventions was an above-knee device that was a kneeling peg leg and foot prosthesis with a fixed position, adjustable harness, and knee lock control. The functionality of his advancements showed how future prosthetics could develop.
Other major improvements before the modern era:
- Pieter Verduyn - First nonlocking below-knee (BK) prosthesis.
- James Potts - Prosthesis made of a wooden shank and socket, a steel knee joint and an articulated foot that was controlled by catgut tendons from the knee to the ankle. Came to be known as “Anglesey Leg” or “Selpho Leg.”
- Sir James Syme - A new method of ankle amputation that did not involve amputating at the thigh.
- Benjamin Palmer - Improved upon the Selpho leg. Added an anterior spring and concealed tendons to simulate natural-looking movement.
- Dubois Parmlee – Created prosthetic with a suction socket, polycentric knee, and multi-articulated foot.
- Marcel Desoutter & Charles Desoutter – First aluminum prosthesis
At the end of World War II, the NAS (National Academy of Sciences) began to advocate better research and development of prosthetics. Through government funding, a research and development program was developed within the Army, Navy, Air Force, and the Veterans Administration.
Lower extremity modern history 
Socket technology for lower extremity limbs saw a revolution of advancement during the 1980s when John Sabolich C.P.O., invented the Contoured Adducted Trochanteric-Controlled Alignment Method (CATCAM) socket, later to evolve into the Sabolich Socket. He followed the direction of Ivan Long and Ossur Christensen as they developed alternatives to the quadrilateral socket, which in turn followed the open ended plug socket, created from wood. The advancement was due to the difference in the socket to patient contact model. Prior, sockets were made in the shape of a square shape with no specialized containment for muscular tissue. New designs thus help to lock in the bony anatomy, locking it into place and distributing the weight evenly over the existing limb as well as the musculature of the patient. Ischial containment is well known and used today by many prosthetist to help in patient care. Variation’s of the ischial containment socket thus exists and each socket is tailored to the specific needs of the patient. Others who contributed to socket development and changes over the years include Tim Staats, Chris Hoyt, and Frank Gottschalk. Gottschalk disputed the efficacy of the CAT-CAM socket- insisting the surgical procedure done by the amputation surgeon was most important to prepare the amputee for good use of a prosthesis of any type socket design.
The first microprocessor-controlled prosthetic knees became available in the early 1990s. The Intelligent Prosthesis was first commercially available microprocessor controlled prosthetic knee. It was released by Chas. A. Blatchford & Sons, Ltd., of Great Britain, in 1993 and made walking with the prosthesis feel and look more natural. An improved version was released in 1995 by the name Intelligent Prosthesis Plus. Blatchford released another prosthesis, the Adaptive Prosthesis, in 1998. The Adaptive Prosthesis utilized hydraulic controls, pneumatic controls, and a microprocessor to provide the amputee with a gait that was more responsive to changes in walking speed. Cost analysis reveals that a sophisticated above knee prosthesis will be in the neighborhood of $1 million in 45 years, given only annual cost of living adjustments.
Current technology/manufacturing 
Over the years there have been significant advancements in artificial limbs. New plastics and other materials, such as carbon fiber, have allowed artificial limbs to be stronger and lighter, limiting the amount of extra energy necessary to operate the limb. This is especially important for transfemoral amputees. Additional materials have allowed artificial limbs to look much more realistic, which is important to transradial and transhumeral amputees because they are more likely to have the artificial limb exposed.
In addition to new materials, the use of electronics has become very common in artificial limbs. Myoelectric limbs, which control the limbs by converting muscle movements to electrical signals, have become much more common than cable operated limbs. Myoelectric signals are picked up by electrodes, the signal gets integrated and once it exceeds a certain threshold, the prosthetic limb control signal is triggered which is why inherently, all myoelectric controls lag. Conversely, cable control is immediate and physical, and through that offers a certain degree of direct force feedback that myoelectric control does not. Computers are also used extensively in the manufacturing of limbs. Computer Aided Design and Computer Aided Manufacturing are often used to assist in the design and manufacture of artificial limbs.
Most modern artificial limbs are attached to the stump of the amputee by belts and cuffs or by suction. The stump either directly fits into a socket on the prosthetic, or—more commonly today—a liner is used that then is fixed to the socket either by vacuum (suction sockets) or a pin lock. Liners are soft and by that, they can create a far better suction fit than hard sockets. Silicone liners can be obtained in standard sizes, mostly with a circular (round) cross section, but for any other stump shape, custom liners can be made. The socket is custom made to fit the residual limb and to distribute the forces of the artificial limb across the area of the stump (rather than just one small spot), which helps reduce wear on the stump. The custom socket is created by taking a plaster cast of the stump or, more commonly today, of the liner worn over the stump, and then making a mold from the plaster cast. Newer methods include laser guided measuring which can be input directly to a computer allowing for a more sophisticated design.
One problem with the stump and socket attachment is that a bad fit will reduce the area of contact between the stump and socket or liner, and increase pockets between stump skin and socket or liner. Pressure then is higher, which can be painful. Air pockets can allow sweat to accumulate that can soften the skin. Ultimately, this is a frequent cause for itchy skin rashes. Further down the road, it can cause breakdown of the skin.
Artificial limbs are typically manufactured using the following steps:
- Measurement of the stump
- Measurement of the body to determine the size required for the artificial limb
- Fitting of a silicone liner
- Creation of a model of the liner worn over the stump
- Formation of thermoplastic sheet around the model – This is then used to test the fit of the prosthetic
- Formation of permanent socket
- Formation of plastic parts of the artificial limb – Different methods are used, including vacuum forming and injection molding
- Creation of metal parts of the artificial limb using die casting
- Assembly of entire limb
Body-powered arms 
Current high tech allows body powered arms to weigh around half to only a third of the weight that a myoelectric arm has.
Current body powered arms contain sockets that are built from hard epoxy or carbon fiber. These sockets or "interfaces" can be made more comfortable by lining them with a softer, compressible foam material that provides padding for the bone prominences. A self suspending or supra-condylar socket design is useful for those with short to mid range below elbow absence. Longer limbs may require the use of a locking roll-on type inner liner or more complex harnessing to help augment suspension.
Wrist units are either screw-on connectors featuring the UNF 1/2-20 thread (USA) or quick release connector, of which there are different models.
Voluntary opening and voluntary closing 
Two types of body powered systems exist, voluntary opening "pull to open" and voluntary closing "pull to close". Virtually all "split hook" prostheses operate with a voluntary opening type system.
More modern "prehensors" called GRIPS utilize voluntary closing closing systems. The differences are significant. Users of voluntary opening systems rely on elastic bands or springs for gripping force, while users of voluntary closing systems rely on their own body power and energy to create gripping force.
Voluntary closing users can generate prehensive forces equivalent to the normal hand, upwards to or exceeding one hundred pounds. Voluntary closing GRIPS require constant tension to grip, like a human hand, and in that property they do come closer to matching human hand performance. Voluntary opening split hook users are limited to forces their rubber or springs can generate which usually is below twenty pounds.
An additional difference exists in the biofeedback created that allows the user to "feel" what is being held. Voluntary opening systems once engaged provide the holding force so that they operate like a passive vice at the end of the arm. No gripping feedback is provided once the hook has closed around the object being held. Voluntary closing systems provide directly proportional control and biofeedback so that the user can feel how much force that they are applying.
Terminal devices 
Terminal devices contain a range of hooks, prehensors, hands or other devices.
Voluntary opening split hook systems are simple, convenient, light, robust, versatile and relatively affordable. Hooks obviously do not match human hand in both appearance and overall versatility.
However, a hook's material tolerances can also exceed and surpass the human hand for mechanical stress (one can use a hook to slice open boxes or as a hammer whereas same is not possible with a hand), for thermal stability (one can use a hook to grip items from boiling water, to turn meat on a grill, to hold a match until it has burned down completely) and for chemical hazards (as a metal hook withstands acids or lye, and does not react to solvents as a prosthetic glove or human skin does).
Prosthetic hands are available in both voluntary opening and voluntary closing versions and because of their more complex mechanics and cosmetic glove covering require a relatively large activation force, which, depending on the type of harness used, may be uncomfortable.
Commercial providers, materials 
Hosmer and Otto Bock are major commercial hook providers. Mechanical hands are sold by Hosmer and Otto Bock as well; the Becker Hand is still manufactured by the Becker family. Prosthetic hands may be fitted with standard stock or custom made cosmetic looking silicone gloves. But regular work gloves may be worn as well. Other terminal devices include the V2P Prehensor, a versatile robust gripper that allows customers to modify aspects of it, Texas Assist Devices (with a whole assortment of tools) and TRS that offers a range of terminal devices for sports. Cable harnesses can be built using aircraft steel cables, ball hinges and self lubricating cable sheaths.
Lower extremity prosthetics 
Lower extremity prosthetics describes artificially replaced limbs located at the hip level or lower. The two main subcategories of lower extremity prosthetic devices are 1.trans-tibial (any amputation transecting the tibia bone or a congenital anomaly resulting in a tibial deficiency) and 2.trans-femoral (any amputation transecting the femur bone or a congenital anomaly resulting in a femoral deficiency). In the prosthetic industry a trans-tibial prosthetic leg is often referred to as a "BK" or below the knee prosthesis while the trans-femoral prosthetic leg is often referred to as an "AK" or above the knee prosthesis.
Other, less prevalent lower extremity cases include the following:
- Hip disarticulations - This usually refers to when an amputee or congenitally challenged patient has either an amputation or anomaly at or in close proximity to the hip joint.
- Knee disarticulations - This usually refers to an amputation through the knee disarticulating the femur from the tibia.
- Symes - This is an ankle disarticulation while preserving the heel pad.
C-Leg knee prosthesis 
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The Otto Bock Orthopedic Industry introduced the C-Leg during the World Congress on Orthopedics in Nuremberg in 1997. The company began marketing the C-Leg in the United States in 1999. Other microprocessor-controlled knee prostheses include Ossur's Rheo Knee, released in 2005, the Power Knee by Ossur, introduced in 2006, the Plié Knee from Freedom Innovations and DAW Industries’ Self Learning Knee (SLK).
The idea was originally developed by Kelly James, a Canadian engineer, at the University of Alberta. The C-Leg uses hydraulic cylinders to control the flexing of the knee. Sensors send signals to the microprocessor that analyzes these signals, and communicates what resistance the hydraulic cylinders should supply. C-Leg is an abbreviation of 3C100, the model number of the original prosthesis, but has continued to be applied to all Otto Bock microprocessor-controlled knee prostheses. The C-Leg functions through various technological devices incorporated into the components of the prosthesis. The C-Leg uses a knee-angle sensor to measure the angular position and angular velocity of the flexing joint. Measurements are taken up to fifty times a second. The knee-angle sensor is located directly at the axis of rotation of the knee.
Moment sensors are located in the tube adapter at the base of the C-Leg. These moment sensors use multiple strain gauges to determine where the force is being applied to the knee, from the foot, and the magnitude of that force.
The C-Leg controls the resistance to rotation and extension of the knee using a hydraulic cylinder. Small valves control the amount of hydraulic fluid that can pass into and out of the cylinder, thus regulating the extension and compression of a piston connected to the upper section of the knee. The microprocessor receives signals from its sensors to determine the type of motion being employed by the amputee. The microprocessor then signals the hydraulic cylinder to act accordingly. The microprocessor also records information concerning the motion of the amputee that can be downloaded onto a computer and analyzed. This information allows the user to make better use of the prosthetic.
The C-Leg is powered by a lithium-ion battery housed inside the prosthesis near the knee joint. On a full charge, the C-leg can operate for up to 45 hours, depending on the intensity of use. A charging port located on the front of the knee joint can be connected to a charging cable plugged directly into a standard outlet. A "pigtail" charging port adapter permits the relocation of the charging port to a location more accessible when the prosthesis has a cosmetic cover applied. The charger cord has lights that allow the user to observe the level of charge when connected to the knee. A 12 volt car charger adapter can also be purchased.
The C-Leg provides certain advantages over conventional mechanical knee prostheses. It provides an approximation to an amputee’s natural gait. The C-Leg allows amputees to walk at near walking speed. Variations in speed are also possible and are taken into account by sensors and communicated to the microprocessor, which adjusts to these changes accordingly. It also enables the amputees to walk down stairs with a step-over-step approach, rather than the one step at a time approach used with mechanical knees. The C-Leg’s ability to respond to sensor readings can help amputees recover from stumbles without the knee buckling. However, the C-Leg has some significant drawbacks that impair its use. The C-Leg is susceptible to water damage and thus great care must be taken to ensure that the prosthesis remains dry. Otto Bock recommends that each amputee use the C-Leg for up to two months before the system can fully become accustomed to the individual’s unique gait. Becoming accustomed to the C-Leg is especially difficult when walking downhill, and amputees should seek help while becoming familiar with the system to avoid injury.
A wide range of amputees can make use of the C-Leg; however, some people are more suited to this prosthesis than others. The C-Leg is designed for use on people who have undergone transfemoral amputation, or amputation above the knee. The C-Leg can be used by amputees with either single or bilateral limb amputations. In the case of bilateral amputations, the application of C-Legs must be closely monitored. In some cases, those who have undergone hip disarticulation amputations can be candidates for a C-Leg. The prosthesis is recommended for amputees that vary their walking speeds and can reach over 3 miles per hour; however, it cannot be used for running. The C-Leg is practical for upwards of 3 miles daily, and can be used on uneven ground, slopes, or stairs. Active amputees, such as bikers and rollerbladers may find the C-Leg suited to their needs.
Certain physical requirements must be met for C-Leg use. The amputee must have satisfactory cardiovascular and pulmonary health. The balance and strength of the amputee must be sufficient to take strides while using prosthesis. The C-Leg is designed to support amputees weighing up to 275 pounds.
A myoelectric prosthesis uses electromyography signals or potentials from voluntarily contracted muscles within a person's residual limb on the surface of the skin to control the movements of the prosthesis, such as elbow flexion/extension, wrist supination/pronation (rotation) or hand opening/closing of the fingers. A prosthesis of this type utilizes the residual neuro-muscular system of the human body to control the functions of an electric powered prosthetic hand, wrist or elbow. This is as opposed to an electric switch prosthesis, which requires straps and/or cables actuated by body movements to actuate or operate switches that control the movements of a prosthesis or one that is totally mechanical. It is not clear whether those few prostheses that provide feedback signals to those muscles are also myoelectric in nature. It has a self suspending socket with pick up electrodes placed over flexors and extensors for the movement of flexion and extension respectively.
Robotic prostheses 
In order for a robotic prosthetic limb to work, it must have several components to integrate it into the body's function: Biosensors detect signals from the user's nervous or muscular systems. It then relays this information to a controller located inside the device, and processes feedback from the limb and actuator (e.g., position, force) and sends it to the controller. Examples include wires that detect electrical activity on the skin, needle electrodes implanted in muscle, or solid-state electrode arrays with nerves growing through them. One type of these biosensors are employed in myoelectric prosthesis.
Mechanical sensors process aspects affecting the device (e.g., limb position, applied force, load) and relay this information to the biosensor or controller. Examples include force meters and accelerometers.
The controller is connected to the user's nerve and muscular systems and the device itself. It sends intention commands from the user to the actuators of the device, and interprets feedback from the mechanical and biosensors to the user. The controller is also responsible for the monitoring and control of the movements of the device.
An actuator mimics the actions of a muscle in producing force and movement. Examples include a motor that aids or replaces original muscle tissue.
Targeted muscle reinnervation (TMR) is a technique in which motor nerves which previously controlled muscles on an amputated limb are surgically rerouted such that they reinnervate a small region of a large, intact muscle, such as the pectoralis major. As a result, when a patient thinks about moving the thumb of his missing hand, a small area of muscle on his chest will contract instead. By placing sensors over the reinervated muscle, these contractions can be made to control movement of an appropriate part of the robotic prosthesis.
An emerging variant of this technique is called targeted sensory reinnervation (TSR). This procedure is similar to TMR, except that sensory nerves are surgically rerouted to skin on the chest, rather than motor nerves rerouted to muscle. The patient then feels any sensory stimulus on that area of the chest, such as pressure or temperature, as if it were occurring on the area of the amputated limb which the nerve originally innervated. In the future, artificial limbs could be built with sensors on fingertips or other important areas. When a stimulus, such as pressure or temperature, activated these sensors, an electrical signal would be sent to an actuator, which would produce a similar stimulus on the "rewired" area of chest skin. The user would then feel that stimulus as if it were occurring on an appropriate part of the artificial limb.
Recently, robotic limbs have improved in their ability to take signals from the human brain and translate those signals into motion in the artificial limb. DARPA, the Pentagon’s research division, is working to make even more advancements in this area. Their desire is to create an artificial limb that ties directly into the nervous system.
Robotic arms 
Advancements in the processors used in myoelectric arms has allowed to make gains in fine tuned control of the prosthetic. The Boston Digital Arm is a recent artificial limb that has taken advantage of these more advanced processors. The arm allows movement in five axes and allows the arm to be programmed for a more customized feel. Recently the i-Limb hand, invented in Edinburgh, Scotland, by David Gow has become the first commercially available hand prosthesis with five individually powered digits. The hand also possesses a manually rotatable thumb which is operated passively by the user and allows the hand to grip in precision, power and key grip modes. Raymond Edwards, Limbless Association Acting CEO, was the first amputee to be fitted with the i-LIMB by the National Health Service in the UK. The hand, manufactured by "Touch Bionics" of Scotland (a Livingston company), went on sale on 18 July 2007 in Britain. It was named alongside the Large Hadron Collider in Time magazine's top fifty innovations.
Another neural prosthetic is Johns Hopkins University Applied Physics Laboratory Proto 1. Besides the Proto 1, the university also finished the Proto 2 in 2010.
Early in 2013, Max Ortiz Catalan and Rickard Brånemark of the Chalmers University of Technology, and Sahlgrenska University Hospital in Sweden, succeeded in making the first robotic arm which is mind-controlled and can be permanently attached to the body (using osseointegration).
Robotic legs 
Attachment to the body 
Most prostheses can be attached to the exterior of the body, in a non-permanent way. Some others however can be attached in a permanent way. One such example are exoprostheses (see below).
Direct bone attachment / osseointegration 
Osseointegration is a new method of attaching the artificial limb to the body. This method is also sometimes referred to as exoprosthesis (attaching an artificial limb to the bone), or endo-exoprosthesis.
The stump and socket method can cause significant pain in the amputee, which is why the direct bone attachment has been explored extensively. The method works by inserting a titanium bolt into the bone at the end of the stump. After several months the bone attaches itself to the titanium bolt and an abutment is attached to the titanium bolt. The abutment extends out of the stump and the (removable) artificial limb is then attached to the abutment. Some of the benefits of this method include the following:
- Better muscle control of the prosthetic.
- The ability to wear the prosthetic for an extended period of time; with the stump and socket method this is not possible.
- The ability for transfemoral amputees to drive a car.
The main disadvantage of this method is that amputees with the direct bone attachment cannot have large impacts on the limb, such as those experienced during jogging, because of the potential for the bone to break.
Cosmetic prosthesis has long been used to disguise injuries and disfigurements. With advances in modern technology, cosmesis, the creation of lifelike limbs made from silicone or PVC has been made possible. Such prosthetics, such as artificial hands, can now be made to mimic the appearance of real hands, complete with freckles, veins, hair, fingerprints and even tattoos. Custom-made cosmeses are generally more expensive (costing thousands of US dollars, depending on the level of detail), while standard cosmeses come ready-made in various sizes, although they are often not as realistic as their custom-made counterparts. Another option is the custom-made silicone cover, which can be made to match a person's skin tone but not details such as freckles or wrinkles. Cosmeses are attached to the body in any number of ways, using an adhesive, suction, form-fitting, stretchable skin, or a skin sleeve.
Unlike neuromotor prostheses, neurocognitive prostheses would sense or modulate neural function in order to physically reconstitute or augment cognitive processes such as executive function, attention, language, and memory. No neurocognitive prostheses are currently available but the development of implantable neurocognitive brain-computer interfaces has been proposed to help treat conditions such as stroke, traumatic brain injury, cerebral palsy, autism, and Alzheimer's disease. The recent field of Assistive Technology for Cognition concerns the development of technologies to augment human cognition. Scheduling devices such as Neuropage remind users with memory impairments when to perform certain activities, such as visiting the doctor. Micro-prompting devices such as PEAT, AbleLink and Guide have been used to aid users with memory and executive function problems perform activities of daily living.
Prosthetic enhancement 
In addition to the standard artificial limb for everyday use, many amputees or congenital patients have special limbs and devices to aid in the participation of sports and recreational activities.
Within science fiction, and, more recently, within the scientific community, there has been consideration given to using advanced prostheses to replace healthy body parts with artificial mechanisms and systems to improve function. The morality and desirability of such technologies are being debated. Body parts such as legs, arms, hands, feet, and others can be replaced.
The first experiment with a healthy individual appears to have been that by the British scientist Kevin Warwick. In 2002, an implant was interfaced directly into Warwick's nervous system. The electrode array, which contained around a hundred electrodes, was placed in the median nerve. The signals produced were detailed enough that a robot arm was able to mimic the actions of Warwick's own arm and provide a form of touch feedback again via the implant.
- Oscar Pistorius
In early 2008, Oscar Pistorius, the "Blade Runner" of South Africa, was briefly ruled ineligible to compete in the 2008 Summer Olympics because his transtibial prosthesis limbs were said to give him an unfair advantage over runners who had ankles. One researcher found that his limbs used twenty-five percent less energy than those of an able-bodied runner moving at the same speed. This ruling was overturned on appeal, with the appellate court stating that the overall set of advantages and disadvantages of Pistorius' limbs had not been considered. Pistorius did not qualify for the South African team for the Olympics, but went on to sweep the 2008 Summer Paralympics, and has been ruled eligible to qualify for any future Olympics. He qualified for the 2011 World Championship in South Korea and reached the semifinal where he ended last timewise, he was 14th in the first round, his personal best at 400m would have given him 5th place in the finals.
At the 2012 Summer Olympics in London, Pistorius became the first amputee runner to compete at an Olympic Games. He ran in the 400 metres race semifinals;, and the 4 × 400 metres relay race finals.
Design considerations 
There are multiple factors to consider when designing a transtibial prosthesis. Manufacturers must make choices about their priorities regarding these factors.
Nonetheless, there are certain elements of socket and foot mechanics that are invaluable for the athlete, and these are the focus of today’s high-tech prosthetics companies:
- Fit - athletic/active amputees, or those with bony residua, may require a carefully detailed socket fit; less-active patients may be comfortable with a 'total contact' fit and gel liner
- Energy storage and return – storage of energy acquired through ground contact and utilization of that stored energy for propulsion
- Energy absorption – minimizing the effect of high impact on the musculoskeletal system
- Ground compliance – stability independent of terrain type and angle
- Rotation – ease of changing direction
- Weight – maximizing comfort, balance and speed
- Suspension - how the socket will join and fit to the limb≈
The buyer is also concerned with numerous other factors:
- Ease of use
- Size availability
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Transradial and transtibial prostheses typically cost between US $6,000 and $8,000. Transfemoral and transhumeral prosthetics cost approximately twice as much with a range of $10,000 to $15,000 and can sometimes reach costs of $35,000. The cost of an artificial limb does recur because artificial limbs are usually replaced every 3–4 years due to wear and tear. In addition, if the socket has fit issues, the socket must be replaced within several months. If height is an issue components can be changed, such as the pylons. 
Low cost above knee prostheses often provide only basic structural support with limited function. This function is often achieved with crude, non-articulating, unstable, or manually locking knee joints. A limited number of organizations, such as the International Committee of the Red Cross (ICRC), create devices for developing countries. Their device which is manufactured by CR Equipments is a single-axis, manually operated locking polymer prosthetic knee joint.
Table. List of knee joint technologies based on the literature review. 
|Name of technology (country of origin)||Brief description||Highest level of
|ICRC knee (Switzerland)||Single-axis with manual lock||Independent field|
|ATLAS knee (UK)||Weigh-activated friction||Independent field|
|POF/OTRC knee (US)||Single-axis with ext. assist||Field|
|DAV/Seattle knee (US)||Compliant polycentric||Field|
|LEGS M1 knee (US)||Four-bar||Field|
|LCKnee (Canada)||Single-axis with automatic lock||Field|
|None provided (Nepal)||Single-axis||Field|
|None provided (New Zealand)||Roto-molded single-axis||Field|
|None provided (India)||Six-bar with squatting||Technical development|
|Friction knee (US)||Weigh-activated friction||Technical development|
|Wedgelock knee (Australia)||Weigh-activated friction||Technical development|
|SATHI friction knee (India)||Weigh-activated friction||Limited data available|
There is currently an open Prosthetics design forum known as the "Open Prosthetics Project". The group employs collaborators and volunteers to advance Prosthetics technology while attempting to lower the costs of these necessary devices.
A plan for a low-cost artificial leg, designed by Sébastien Dubois, was featured at the 2007 International Design Exhibition and award show in Copenhagen, Denmark, where it won the Index: Award. It would be able to create an energy-return prosthetic leg for US $8.00, composed primarily of fiberglass.
Prior to the 1980s, foot prostheses merely restored basic walking capabilities. These early devices can be characterized by a simple artificial attachment connecting one's residual limb to the ground.
The introduction of the Seattle Foot (Seattle Limb Systems) in 1981 revolutionized the field, bringing the concept of an Energy Storing Prosthetic Foot (ESPF) to the fore. Other companies soon followed suit, and before long, there were multiple models of energy storing prostheses on the market. Each model utilized some variation of a compressible heel. The heel is compressed during initial ground contact, storing energy which is then returned during the latter phase of ground contact to help propel the body forward.
Since then, the foot prosthetics industry has been dominated by steady, small improvements in performance, comfort, and marketability. Jaipur Foot, an artificial limb from Jaipur, India, costs about US$ 40.
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