by Ariola Bardhi
The origin of prosthetics dates back to the early civilizations of Egypt, Greece and Rome, when prosthetic limbs were made out of fiber, wood, iron, and bronze.   Brutal war battles throughout world history have resulted in extraordinary mortality and morbidity, including grotesque injuries and the loss of limbs. These innumerable war casualties have provided impetus for the improvement of artificial limb design. The French army surgeon, Ambroise Paré, who is often considered to be the father of modern prosthetic surgery and design, was the first to develop an artificial iron leg with an articulated knee-joint in 1529.   After the U.S. Civil War in the early 1860s, the large number of veterans having amputations increased the interest and governmental funding for artificial limbs. A prosthesis with a suction pocket and a multi-articulated foot were designed by Dubois Parmlee during this time.  After World War II, which pushed the advancement of prosthetic device design even further, the National Academy of Sciences established the Artificial Limb Program.  There became a new emphasis on the movement and functionality of artificial limbs, resulting in the invention of the above-the-knee and below-the-knee prostheses in 1945 and 1975, respectively. 
The above-the-knee prosthesis improved the design of prostheses and recovery for amputations high up the thigh, and the below-the-knee prosthesis gave the amputees better control and easier adoption compared to earlier devices, since it retained the amputee’s knee. In the 1980s the Contoured Adducted Trochanteric-Controlled Alignment Method (CAT- CAM) socket was invented improving general patient rehabilitation, as it was shown in clinical trials.    Microprocessors began to be incorporated into the design of external prostheses beginning in the early 1990s, an innovation representing a great leap toward the development of ever-improving artificial limb designs that enhance control by the patient. 
Today a variety of options for artificial limbs are available. New advancements include the microprocessor-controlled C-leg, the battery-powered PowerKnee, the PowerFoot, and the myoelectric iLimb, amongst others.     They reflect improvements in the materials used (such as carbon fiber), attachment methods, and fit between the stump and the socket. The addition of microprocessors and other computer-aided designs further improved the use and functionality of prostheses. The stump is usually fixed into the socket by vacuum, or by a pin lock. This can be problematic, because anything less than a perfect fit can cause discomfort to the amputee, from minor skin irritations to painful sores. This can be avoided through another attachment method called osseointegration.  A titanium screw is inserted into the bone of the amputated limb, and after it is properly positioned, a linker is added that attaches the artificial limb to the titanium bolt. As one can imagine, this method is permanent, and can provide many advantages depending on the lifestyle of the patient.
Myoelectric prostheses represent another advancement in artificial limb technology. They use electromyography (EMG) signals from voluntarily contracted muscles within the amputee’s residual limb to control the movement of the artificial limb. A small electrode attached to the surface of the skin records an EMG signal. The signal is amplified and processed by motors located in the hand, wrist, or elbow to produce movement.  In 2001 The Rehabilitation Institute of Chicago developed the targeted muscle reinnervation (TMR) prosthesis, which is an advancement of the myoelectric prostheses. In TMR the nerves from the amputated limb are rerouted to intact, healthy muscle in the body, such as chest muscles, allowing for the movement of the prosthetic limb by thinking about the action to be performed. The nerve impulses generated by thought are sensed by surface electrodes attached to the surface of the muscle, where the nerves have been rerouted, and carried to the artificial limb to generate movement.   In November 2012 Zac Vawter successfully used his TMR myoelectric leg to climb 103 floors of Chicago’s Willis Tower.  This was an exciting event that validated the success of TMR technology. However, TMR uses residual nerves from the amputated limb, and the patient does not generate movement by electrical signals in the brain sent directly to the prosthetic device. Is it possible to have a prosthetic limb that is controlled directly by the brain?
Researchers at Chalmers University of Technology in Sweden are currently addressing the question. They are determined to develop a limb that can be controlled by direct neural feedback.   Researchers plan to use osseointegration in combination with neural and muscular electrodes that will be placed on the stumps, and algorithms that will translate thought into movement. A clinical trial is currently underway to test the efficacy of their invention. 
Other groups are currently developing innovative ideas for prosthetic technology as well. In a collaborative effort between research groups from University of Alabama, University of Virginia, Vanderbilt University, and Georgia Institute of Technology, they are trying to use monopropellants, a type of liquid fuel, to develop a lightweight prosthesis with enough energy to power a day’s worth of routine operations. This system will require a sleeve muscle actuator, which is very compact and has similar properties to the biological skeletal muscle.  The second research group is the Walk Again Project, a collaboration between the Duke University Center for Neuroengineering, the Technical University of Munich, the Swiss Federal Institute of Technology in Lausanne, and the Edmond and Lily Safra International Institute of Neuroscience of Natal in Brazil. This group is working on the development of a body suit, also called an “exoskeleton,” which will contain the artificial limb and be connected wirelessly to a computer that controls the motor signals of the exoskeleton. The brain will control movement through electrodes implanted under the skull, particularly on the motor cortex area of the brain. A new sensor has been developed at Duke that picks up microwaves throughout the 3-D cortex, and recording systems that contain them are currently being tested on monkeys. 
As we wait for the results of these new advancements in prosthetics, it is clear that the field is moving toward more energy efficient and mind-controlled artificial limbs. What is very exciting, is that the inventions that are currently being tested right now will not only improve the lives of amputees significantly, but they might also provide the technology to restore motility in patients with Parkinson’s disease, or other disorders that disrupt motor behaviors. 
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