IEEE Technology and Society Magazine - June 2015 - 73

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limbs [17]. Several polydigital myoelectric hand prostheses, with greater degrees of freedom than the traditional opening/closing hand, are already commercially
available. Nonetheless, rigorous clinical studies of the
performance and advantages offered by these devices
are still lacking.

Recent Technological Advances

FiguRe 2. A soldier in the U.S. Army plays fooz-ball with
two prosthetic limbs: one mechanical (right arm) and one
myoelectric (left arm). Courtesy of the U.S. Army, by Walter Reed
photographers.

the loss of one or both upper limbs has huge consequences on the person's capacity to carry out activities
of daily living as well as impacting their professional life
and autonomy. Amputation is considered to be a public
health issue because of "the repercussions of the deficit
related to the loss of all, or part of, one or both upper
limbs on socio-professional and family life" [15]. This is
consistent with the analysis of disability conceptualized
by the International Classification of Functioning, Disability, and Health (ICF) [16].
Three different types of prostheses are currently available to patients: non-functional (cosmetic) prostheses,
and functional ones, among which (see Figure 2) mechanical prostheses (controlled by the remaining joints or the
opposite limb via a cable) and myoelectric prostheses
which use surface electromyograms (sEMG) of the voluntary electrical activity of the residual muscles of the
stump to control the electrical actuators of the prosthesis.
The latter are commonly placed under the term "robotic"
prostheses although "robotic" prostheses relate to recent
myoelectric prostheses that integrate automation, e.g..
automatic tightening of the hand when a grasped object
begins to slip, or advanced control technologies, such
as the automatic posture generation offered on recent
polydigital hand prostheses.
Commercial companies mostly propose hand and
forearm prostheses for forearm amputations (the most
common upper limb amputation), as well as a few
elbow prostheses. Naturally, because of the small size
of the market, there are fewer prostheses available for
transhumeral (above the elbow), and even fewer for
higher levels of amputation.
Most research institutes and companies focus on
improving the hardware of hand devices, the design
of which is coming closer to that of humanoid robotics
june 2015

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Beyond improvements in hardware, significant progress
has been made both in devices developed by research
laboratories and in commercial prosthetics. The additional
progress has been in the areas of control techniques, sensory feedback, and the development of new materials.
For example, researchers from the Rehabilitation Institute of Chicago (RIC) have developed an innovative surgical technique called "targeted muscle reinnervation." This
technique involves the surgical rerouting of motor nerves
of the sectioned limb to a group of surgically deinnervated muscles in the thoracic wall [18]. Following a learning process, the subject controls these muscles exactly
as he/she controlled the missing limb. Electrodes are
implanted within the muscles in order to capture the EMG
signal sent by the brain, which thinks it is controlling the
arm. This signal is then used to drive the prosthesis. This
method can be used to control prostheses with a large
number of active joints, avoiding sequential control (joint
by joint). More recently, electrodes have been implanted
in the cortex of the brain of tetraplegic patients with a
total loss of mobility. During these short-term trials (one
month for ethical-legal reasons), including an intensive
learning phase, the patients were able to use an external
robotic arm to carry out activities of daily living [19].
Sensory information is essential for the performance of
motor activities (in neurosciences the term sensory-motor
control is used, rather than motor control). Much research
is therefore focused on restoring the sensations of interaction of the prosthesis with the environment. The aim is to
improve fine control (such as the degree of force exerted
by the hand), and to reduce the necessity for intense visual
control. The technique involves placing force/pressure sensors in the prosthetic fingers and returning the information
to the patient via another modality (usually vibro-tactile) to
the residual part of the limb [20]. An alternative invasive
approach has recently been tested on one patient. In [21],
information on touch and interaction forces measured on
a prosthetic hand was translated into electrical stimulations sent to electrodes directly implanted into the peripheral nerves of an amputated patient. Using this sensory
feedback, the blindfolded patient was able to recognize
different objects by their feel and shape and to adapt his
grasping strategy accordingly.
Several less "robotic" innovations have also improved
the quality of prostheses, as well as their comfort. The use
of new materials (plastics, composites, light metal alloys)

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Table of Contents for the Digital Edition of IEEE Technology and Society Magazine - June 2015