Prosthetic Arm Acts Like A Real Limb

Main Category: Medical Devices / Diagnostics
Also Included In: Neurology / Neuroscience;  Rehabilitation / Physical Therapy
Article Date: 06 Feb 2007 - 16:00 PDT

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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."

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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

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