Help at hand
Accelerometers are at the heart of a medical implant that improves mobility for stroke sufferers. Lou Reade reports
A Europe-wide research project to design intelligent implants is using accelerometers – as used in the Nintendo Wii games console – to help stroke sufferers regain the use of their hands.
Stimugrip, designed by FineTech Medical, helps patients with an upper motor neuron lesion to extend their wrist and open their hand. The research is part of the pan-European Healthy Aims project to develop intelligent medical implants and diagnostic systems using a range of micro-, bio- and nano-technologies.
Stimugrip senses the user’s own movements and uses this information to stimulate nerves that have been left ineffective following a stroke. There are two main parts to the system; a two-channel stimulator, which is implanted in the arm; and an external controller.
An accelerometer in the controller, which is worn on the outside of the arm, talks to the implant on the inside of the arm through an inductive coupling – the method used to charge an electric toothbrush.
The surgical procedure is to make an incision in the forearm and attach electrodes to the appropriate muscles. The receiver is attached to the electrodes and put into the forearm, then the incision is closed.
John Spensley, managing director of Finetech Medical, said: “If you had your arm down by your side and lifted in a horizontal fashion this could trigger the opening of the hand.”
The way in which each individual user ‘triggers’ the device can be very complex.
“Triggering can be quite complicated because all users are different and have often been coping with restricted movement for years,” says Spensley. “The trigger can even change as the user regains movement – as they start to move in a different way.”
Paul Taylor, a biomedical engineer from The National Clinical FES Centre in Salisbury, which is conducting clinical trials on Stimugrip on five people, said: "Volunteers have reported that they are more aware of their affected arm, and now spontaneously use it in daily life – where as before they would ignore it. For one volunteer this is the first time in 47 years.
“Improvements have been seen in measures of hand function, disability, activities of daily living and quality of life,” he concluded.
Stimugrip is based on Stimustep, an earlier system to treat another stroke-related condition called dropped foot – which renders patients unable to raise their foot during the swing phase of walking. Previously, the condition was managed by fixing the ankle joint with a brace and electrical stimulation of a nerve through the skin. This can be quite uncomfortable.
Using Stimustep, a foot switch under the heel detects when the heel leaves the floor during walking. A signal is then sent to the transmitter, which sends power and signals to the implanted receiver. Electrical pulses are then delivered to nerves supplying muscles around the ankle. Once the heel touches the ground again, the stimulation is switched off, in readiness for the next cycle.
Because the implanted is directly attached to appropriate nerves, the problems of electrode placement are eliminated. At the same time, stimulation is less painful because the stimulation current does not pass across the skin, says FineTech.
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