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The FineTech Dropped Foot System is a new device currently undergoing clinical trials for the treatment of dropped foot, a chronic condition suffered by stroke patients and others and characterised by the inability to raise the foot during the swing phase of walking. People who suffer from this problem tend to have a laboured and unsafe gait, needing to hitch and circumduct their hip in order to swing their hemiplegic leg clear of the ground. The increased energy expenditure needed leads to fatigue, further reduction in the speed and distance walked, and often a further increase in spasticity. The current approaches for dropped foot correction are fixation of the ankle joint by a brace, or electrical stimulation applied to a nerve in the leg through electrodes attached on the skin surface (surface stimulation). However, there can be significant drawbacks associated with surface stimulation. For example, in order to achieve the correct movement of the foot, the surface stimulation approach requires accurate placement of the electrodes, which is both difficult and rather time consuming. Also, with the surface approach, discomfort or pain can occur, either as a result of a skin reaction to the electrodes, or as a result of electrical current passing through the skin.The FineTech System, in contrast to the surface stimulators, has an implanted part that is directly attached to appropriate nerves and therefore the problems of electrode placement have been eliminated. Also, stimulation will be less painful, as the stimulation current does not pass across the skin. The other novel aspect is that the system has two stimulation channels, this allows for a certain degree of adjustment of the resulting foot movement. The stimulator can be thought of in two parts; the implant, which the surgeon will place under the skin of the leg and the external equipment (transmitter, belt, charger and switch). More extensive details on the implant are available on request. The basic operation of the system is as follows. The foot switch located under the heel detects when the heel leaves
the floor during walking. When this happens, a signal is sent along
the wire connecting the heel switch to the transmitter and the
transmitter becomes active, transmitting power and signals to the
implanted receiver. The level of stimulation on each channel is
set by adjustment of the transmitter. The signals are transformed
by the receiver and result in electrical pulses being delivered
to nerves supplying muscles around the ankle. Soon after the heel
touches the ground again, the stimulation is switched off, in readiness
for the next time that the heel leaves the ground. In some cases,
it is possible that the heel will not touch the ground at the next
step and in these cases, stimulation will automatically be turned
off after four seconds. |
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