Functional electrical stimulation for drop foot of central neurological origin

Drop foot can be caused by upper or lower motor neurone lesions. Functional electrical stimulation is used to treat the effects of upper motor neurone lesions that can result from conditions such as stroke, cerebral palsy, multiple sclerosis or spinal cord injury but may occur in other conditions. Symptoms and signs of upper motor neurone lesions include muscle weakness in a pyramidal distribution (an imbalance causing arm flexion and leg extension), hypertonicity, exaggerated reflexes, clonus and an extensor plantar response. Functional electrical stimulation is not normally suitable for patients with lower motor neurone lesions.

Treatment options include physiotherapy or an ankle-foot orthosis to align the lower leg and control the motion of the ankle and foot, providing stability and improving gait. Medical therapy includes oral administration of muscle relaxant drugs or botulinum toxin type A injections. Surgery (usually reserved for refractory cases) includes selective tendon release of muscles.

Functional electrical stimulation aims to produce muscle contractions that mimic normal voluntary gait movement (lifting the foot and achieving correct placement on the ground) by applying electrical pulses to the common peroneal nerve through skin surface or implanted electrodes.

Various devices can be used for this procedure. Implanted functional electrical stimulation (FES) electrodes are usually inserted into the epineurium of the peroneal nerve under general anaesthesia. The electrodes are either percutaneous (passed through the skin and connected to an external pulse generator) or fully implanted (operated by radiofrequency waves). In skin surface FES, electrodes placed over the nerve are connected by leads to a stimulator unit and controlled with a foot switch.

Patients may also use ankle-foot orthosis.

A meta-analysis (including three controlled studies) of 71 patients with stroke reported a mean increase of 0.18 metres/second (95% confidence interval [CI] 0.08 to 0.28) in gait speed in 36 patients treated by skin surface FES compared with 35 patients treated by conventional therapy (absolute numbers not given).

A case series including 111 patients with stroke treated by skin surface FES reported a mean increase in walking speed of 27% (p<0.01) and a reduction in effort of 31% (p<0.01), assessed with stimulation at 18 weeks. Corresponding improvements in speed and effort without stimulation were 14% (p<0.01) and 19% (p<0.01) respectively.

A randomised controlled trial (RCT) of 29 patients with stroke reported a 23% improvement in walking speed (during daily activity) in the 14 patients treated by implanted FES (assessed with stimulation), compared with 3% in the 15 patients who had conventional therapy (follow-up: 26 weeks; p=0.010).

A second RCT of 29 patients with stroke, of whom 14 were treated by implanted FES over 12 weeks, reported subjective achievement of functional milestones (such as 'prepared dinner', 'walked outside') in 53 instances in the FES group and 11 instances in the conventional therapy group (assessed by bimonthly questionnaires; follow-up not stated).

The Specialist Advisers considered key efficacy outcomes to include improved gait, reduction in effort when walking, reduction in pain and discomfort, reduction in falls, return to work and other quality of life outcomes.

In an RCT of 29 patients with stroke, 14 of whom received implanted electrodes (percutaneous), there were four reports of skin erythema. In a case series of 17 patients who all received implanted electrodes (percutaneous), 14 cases of skin erythema were reported in 6 patients (1 of the 6 required electrode removal). A case series of 15 patients who received implanted electrodes (radiofrequency) reported wound infection in 2 patients. The second RCT of 29 stroke patients (14 of whom had implanted electrodes [radiofrequency]) reported one instance of device malfunction after 10 weeks.

The Specialist Advisers noted anecdotal adverse events included an increase in seizure incidence among patients with epilepsy, autonomic dysreflexia in patients with spinal cord injuries, problems with computed tomography (CT) or magnetic resonance imaging (MRI) scanning with implanted electrodes, increases in spasticity or spasms, infection when using implanted systems, and skin intolerance. They considered theoretical adverse events to include muscle fibrillation, problems caused by faulty equipment, or problems when treating pregnant women or patients who have a pacemaker.

The Committee noted that most of the evidence related to patients with stroke; that there are a number of different FES devices; and that the technology is evolving.

The Committee noted that interpretation of the evidence was difficult because the evidence is based on studies that used different methods of applying the procedure (skin surface or implanted).