Do you trip or fall? Could FES help?
Jon Graham, Clinical Director, PhysioFunction.

Many stroke survivors find that they catch the toes of their affected leg as they swing it forwards. This is often because they are unable to lift the foot up at the ankle. The technical term for this is drop foot (or foot drop). It is caused by weakness from the stroke of the muscles at the front of the shin. Tightness or spasticity in the calf muscles can add to the difficulty of lifting the foot.

The most common solution for this is the use of a plastic splint worn in the shoe called an Ankle Foot Orthosis (AFO), or a metal calliper attached to the shoe. These fix the foot at a suitable angle so that the toes can clear the ground.

In the USA in the 1960s, researchers found that it was possible to stimulate the nerves supplying the foot lifting muscles using tiny electrical currents. This was termed Functional Electrical Simulation (FES). In the mid 1990s, the Medical Physics Department at Salisbury District Hospital produced the Odstock Drop Foot Stimulator (ODFS) which enabled this technology to be used practically outside of the laboratory. The ODFS uses a small footswitch placed discreetly in the heel of the user’s shoe. When the weight comes off the heel, the switch triggers the stimulator which then conveys the electrical current via sticky electrode pads to the muscle and the nerve supplying it. The muscle is then activated and the foot lifts up at the ankle.

Not only does FES reduce trips and falls, it can also make walking faster and less effortful. Overtime the muscles can even relearn how to lift the foot without the stimulator. The National Institute for Clinical Excellence (NICE) has declared FES as a safe and effective treatment for drop foot.

The ODFS has been further refined and is now called the PACE. It still relies on wires: one from the foot switch to the stimulator and one from stimulator to the electrode pads. Users have to position the pads for themselves.

Recently two wireless stimulators have become available in the UK: Walkaide and Bioness. Both these devices contain the electrode pads in specially shaped anatomical cuffs that fit just below the knee. The Walkaide has a built in movement sensor that is trained to trigger the stimulator as the user starts to swing their leg forward. The Bioness L300 uses a wireless footswitch to ensure effective triggering with every step. The absence of wires and the housing of the electrodes in the cuff makes these devices easy to put on with one hand - which is so important for many FES users Many PCTs will fund the PACE FES at the National FES Centre at Salisbury or at one its UK-wide satellite clinics. Walkaide and Bioness L300 are generally funded privately. However, PCTs have responded favourably in some cases to funding applications for these devices. The government-backed Access to Work Scheme has also assisted in providing funds for these as mobility aids.

An alternative to surface electrodes is to use implanted electrodes. This requires surgery to position the electrodes directly on the peroneal nerve. Otto Bock ActiGait uses a cuff around the nerve with four channels of stimulation allowing for very selectivestimulation of the nerve to achieve the optimum foot movement. The control unit, positioned at the waist, is wirelessly linked to the foot switch and the implanted cuff, resulting in both a practical and cosmetic solution.

For further reference:

ODFS/PACE:/NHS FES Services www.odstockmedical.com

Walkaide: www.walkaide.com

Bioness: www.bioness.com

Otto Bock: www.ottobock.co.uk

For independent information and advice on all FOUR FES systems:

www.physiofunction.co.uk (East Midlands, Yorkshire, Oxford, London)

www.fesnorthwest.co.uk (Cumbria. Lancashire)