Advances in Prosthetic Limbs

Advances in Prosthetic Limbs

In the year 2000, archaeologists in Cairo, Egypt discovered the mummified remains of a noblewoman. The 3,000 year old remains had a prosthetic toe made of wood and leather. During the Second Punic War, Roman general Marcus Sergius lost his hand in battle. He had a prosthetic hand fashioned from iron so that he could hold his shield and return to battle. In the Dark Ages, knights had prosthetic limbs fashioned from iron which were designed by the same people who made their armor. In the 16th and 17th centuries, more advances came along, such as hinged mechanical hands, locking knees and specialized harnesses. After World War II, the Artificial Limb Program was started in response to the great number of soldiers who had lost limbs in the war.

So how have prosthetics advanced in modern times? Like many technological advances, the past century has seen incredible growth in prosthetics. In 2012 at the Summer Olympic Games in London, South African sprint runner Oscar Pistorius became the first amputee to compete at an Olympic Games. His prosthetics were ‘blades’ designed for running. Also in 2012, Amy Purdy entered The Amazing Race game show on CBS. She is the top ranked adaptive snowboarder of 2011. And activist and amputee Heather Mills appeared on both Dancing with the Stars and Dancing on Ice.

Prosthetic Limb Materials and Designs

For the past several centuries, prosthetics have been made from wood, leather and metal. Recently, plastics and carbon-fiber composites have been used. These more flexible materials have allowed for advancements making prosthetic limbs lighter and stronger.

Prosthetic limb design also can look realistic or be specialized for different tasks. The basic design elements are the same for most limbs:

  • The pylon – this is the internal frame and structure of the prosthetic limb. In the past these were made from wood. Later, metal rods were used and today carbon-fiber elements can be used to provide more flexibility. The pylon may them be covered in a foam-like substance which can be dyed to match skin tone.
  • The socket – this is the part of the prosthetic limb that joins with the patient’s residual limb. Fit is critical in developing the socket in order to avoid irritation or damage to the residual limb. Many patients use padding or prosthetic socks to make sure the fit is comfortable.
  • The suspension system – this is the method for attaching the prosthetic limb to the residual limb. Originally leather harnesses were used. Today, in addition to harnesses, there are simple attachments that rely on suction with the residual limb.

Prosthetic Limb Control

Perhaps the greatest advances have happened in prosthetic limb control. There are cosmetic prosthetic limbs called cosmesis that are designed solely for appearance. These prosthetic limbs do not have the functionality that many patients require. Functional prosthetic limbs can be controlled in several ways:

  • Body powered prosthetic limbs – these are controlled by wires connecting to other parts of the body. A prosthetic arm, for example, may then be controlled by movements in the opposite arm or shoulder.
  • Externally powered prosthetic limbs – these are controlled by switches which activate motors in the prosthetic limb. The patient uses other body parts or the residual limb to toggle the switched in different combinations to achieve the desired motion.
  • Myoelectric prosthetic limbs – these are attached to muscles with electrodes. The myoelectric prosthetic limb ‘listens’ to the muscles which tell the prosthetic limb what to do.
  • Targeted Muscle Reinnervation (TMR) prosthetic limbs – these cutting edge prosthetic limbs were invented by Dr. Todd Kuiken at the Rehabilitation Institute of Chicago. When a limb is lost, the brain still functions as if the limb is there. So if a patient wants to move a lost arm, the brain will send the signals through different nerve endings up to the point of amputation. The signal dies there. With TMR, surgery is performed to redirect signals through nerve endings to another part of the body. For example, if a patient loses their arm, then the surgeon would redirect the path from the arm to a spot on the chest. This would cause movement in the chest. Electrodes are then placed on the chest and whenever the patient want to move their arm, the prosthetic limb is triggered through the chest. The patient is quite literally moving the prosthetic limb with their brain.

Prosthetic Limb Senses

Finally, the most recent project is being worked on by mechanical engineer Jeremy Fishel and involves prosthetic hands. These hands have 3 fingers with sensors on the tip of each finger called BioTacs. The BioTacs sense pressure, temperature and vibration. This allows the hand to adjust. Scientists are currently working on ways to send the touch feedback to the patient. An excellent article detailing their progress can be found here

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