Procedure FES set-up

At the start of the FES phase, there will be an individual FES set-up meeting per patient with the physiotherapist and physician (hereafter called: the therapist, ‘he’), consisting of:

Electrodes positioning

The patient receives an explanation regarding the procedure. Next, the therapist identifies the head of the fibula while the patient is in supine position and he marks it with a moon-shaped line inferior-posterior of the bone. He moistens this area and uses the MiniStim peripheral nerve stimulator to identify the location with the best motor-response of the tibialis anterior muscle, by moving the MiniStim along this line, while applying a bit of pressure and gradually increasing the current. In general, a dorsiflexion motor response is needed, eventually with a bit of eversion. The therapist puts his hand on the tibialis anterior muscle to feel if contraction occurs, and marks the appropriate stimulation place. This is the position for the black electrode of the FES device, over (the deep branch of) the peroneal nerve. The red electrode is placed on the upper 1/3 of the tibialis anterior muscle belly. The therapist checks the motor response with the ‘stimulation’ button of the FES device and adjusts the electrodes position if necessary. It should be kept in mind that pressure applied on the electrodes can influence the effect.

Fitting of the device

The therapist places the cuff of the FES device (including Velcro electrode locators) over the electrodes and the device on the medial side of the lower leg. The orange indicator in the cuff (Fig. 2) should point to the middle of the patella. The position of the indicators (top and bottom of the WalkAide cuff) is marked with a surgical skin marker, to help the patient or parents put it in the correct position.

Timing of the stimulation

The WalkAide device positioned on the leg. The orange indicator at the top is visible. Image:© 2020 Innovative Neurotronics, Inc., All rights Reserved. Usage in paper allowed

Surface electromyography (sEMG) is used to evaluate the timing of the stimulation during the gait cycle. This is more precise than relying on the ‘auditive feedback’ from the WalkAide device that can be turned on to hear the timing of the stimulation during walking. With a quick set-up of three markers on the foot (caput of metatarsal bone 2 and 5 and the heel) and one sEMG sensor on the tibialis anterior muscle, the on/off timing of the stimulation during the gait cycle can be visualized in a 3D gait laboratory. This set-up is not used for gait analysis but only for evaluation of the timing of the stimulation. Figure 3 shows the FES stimulation in the EMG as big spikes. The goal is to let the stimulation start just after toe-off and let it stop just after heel strike. In the WalkAnalyst software, it is possible to adjust the thresholds for on/off and the durations of stimulation and no stimulation.

Stimulus intensity

Spikes of functional electrical stimulation (FES) are visible in electromyography (EMG). X axis: 100 frames per second (100 Hz). Figure from the authors

Patients need time to get used to the electrical stimulation. Therefore, it is advised to gradually increase the stimulus intensity and the wearing time in the first four weeks: at the start, regular breaks from the stimulation are advised every hour. This can be done by turning the device off, or sitting still, because the device won’t stimulate without movement. The use of FES can be gradually increased to 6–8 h a day. The stimulus intensity of the WalkAide device can be turned up from zero to eight (maximum 121–200 mA depending on the resistance. The resistance mainly depends on the condition of the electrodes: new, clean electrodes have lower resistance and maximum stimulus of 200 mA.) (Fig. 4). At the set-up meeting, the effective stimulus intensity, i.e. the intensity that elicits a visible muscle contraction, will be determined, both in standing and walking condition. The patient decides on the intensity that is comfortable for this moment. The therapists explains the patient to increase the intensity in the coming days to weeks if necessary. Further explanation on the device, including side effects such as skin irritation, are provided, together with the device manual and spare batteries (AA batteries).

Follow-up

Buttons on the WalkAide device. Image:© 2020 Innovative Neurotronics, Inc., All rights Reserved. Usage in paper allowed

A check-up appointment will be scheduled 2 weeks after the initial set-up. Patient and parents are asked about their positive and negative experiences. Device positioning by the patient or parents will be verified, the skin is checked for irritations and the stimulus intensity is reviewed.