Prosthetic Arm Acts Like A Real Limb
A new technique - targeted muscle reinnervation* -- that allows a
neuro-controlled prosthetic arm to move as if it is a real limb, is
reported in an Article in this week's issue of
The Lancet.
Currently, most prosthetics are not linked to muscles or connected to
the nerves of the amputated area, and only allow a single motion to be
controlled at a time - the operation of a prosthetic elbow, wrist and
hand, or hook must be done sequentially, and movements are
frustratingly slow and awkward. Added to this, current prostheses have
no intrinsic sense of touch and have little sensory feedback to the
user, and are instead operated only with visual feedback.
Todd Kuiken (Neural Engineering Center for Artificial Limbs,
Rehabilitation Institute of Chicago, USA) and colleagues developed a
new technique called targeted muscle reinnervation that allows improved
control of a motorised prosthetic arm**. The authors conducted targeted
reinnervation surgery on a woman with a left arm amputation at the
humeral neck. This procedure allows the re-routed nerves to grow into
the appropriated muscle and direct the signals they once sent to the
amputated arm to the robotic arm via surface electrodes instead. This
gave the patient better functional movement in her arm, and she
reported using her neuro-controlled prosthesis for many hours a day.
Furthermore, using targeted sensory reinnervation,*** the sensation
nerves to the hand were re-routed to a patch of skin on the patient's
chest, and now when the patient is touched on this skin, she feels that
her hand is being touched. This should eventually let her 'feel' what
she is touching with an artificial hand, as if she were touching it
with her own hand.
The authors conclude: "This patient and our other three patients
represent early application of the targeted reinnervation technique.
Whether the improved function is enough to keep these patients wearing
their devices in years to come, or whether they adapt to their new
control even better and show greater functional gains, remains to be
seen. Long-term follow-up is also needed to see how our patient's
transfer sensation evolves."
###
Katie Lorenz, Rehabilitation Institute of Chicago, USA.
* Targeted muscle reinnervation uses the residual nerves from an
amputated limb and transfers them onto alternative muscle groups that
are not biomechanically functional since they are no longer attached to
the missing arm. During the nerve transfer procedure, target muscles
are denervated so that they can be reinnervated by the residual arm
nerves that previously travelled to the arm before amputation.The
reinnervated muscles than serve as biological amplifiers of the
amputated nerve motor commands. This technique thus provides
physiologically appropriate electromygram control signals that are
related to previous functions of the lost arm.
**See accompanying video on The Lancet website
http://www.thelancet.com/
*** Using this technique, a segment of skin near or overlying the
targeted sensory reinnervation site is denervated and the regenerating
afferent nerve fibres from the residual hand nerves are enabled to
reinnervate this area of skin. As a result, when the skin is touched,
the amputee feels as if their hand is being touched.
Contact: Joe Santangelo
Lancet
