Elsevier

World Neurosurgery

Volume 84, Issue 6, December 2015, Pages 2037-2042
World Neurosurgery

Technical Note
New Therapeutic Option for Drop Foot with the ActiGait Peroneal Nerve Stimulator—a Technical Note

https://doi.org/10.1016/j.wneu.2015.06.074Get rights and content

A drop foot occurs in up to 20% of stroke patients and leads to an increased risk of falls. Until recently, only a foot orthosis or surface stimulation was able to improve the gait of these patients. Recent studies have shown that direct peroneal nerve stimulation with an implantable 4-channel peroneal nerve stimulator (ActiGait) allows independent electrode adjustment and leads to better functional results and an improved quality of life. The application of this therapeutic option is restricted to patients with a drop foot attributable to a lesion of the first motor neuron caused by stroke, multiple sclerosis, or tumors. In this paper, we present the first technical note with possible pitfalls of the surgical procedure and the perioperative care after implantation of ActiGait drop foot stimulators in 50 patients.

Introduction

Spastic paresis of the lower limbs with a drop foot occurs in 20% of stroke patients (10) and may also be caused by cerebral tumors and multiple sclerosis. The patients are not able to actively dorsiflex the foot during the swing phase of the gait (4). Thus undesirable compensatory movement patterns, decreased gait velocity, restricted functional mobility, and an increased risk of falls may result. Ankle foot orthosis and surface stimulation of the peroneal nerve were shown to improve the gait of the patients 1, 12, 14. Comparing those 2 therapeutic options, no significant difference in gait speed was found in a randomized single-blinded trial. However, user satisfaction was significantly higher in the surface stimulation group. The therapeutic effect was reported to be significant over an observed time period of 12 months (8). Furthermore, there is evidence that a chronic use of the surface stimulator strengthens the activation of the motor cortex and their descending connections, which may result in an improvement of the gait even when the stimulator is off after long-term use (6). The main problems of the surface stimulation are the inconvenience in handling the external parts, especially in putting on and taking off of the components; in finding the right stimulator position on the skin; and in skin irritations due to the external stimulator (16). Addressing these issues was attempted through the use of implantable stimulators; however, the first implanted 1-channel stimulators failed to provide a balanced stimulation of inversion and eversion of the ankle (13). A 2-channel stimulator that showed a better selectivity of the stimulation (9) was developed, but it achieved only moderately increased walking speed (7). Recent studies revealed a promising new symptomatic therapy option of stroke-related drop foot through implantation of the ActiGait drop foot stimulator 2, 3, 5. This was confirmed by a prospective study with 27 patients (11). The ActiGait drop foot stimulator is an implantable 4-channel peroneal nerve stimulator with independent electrode adjustment. This allows a more specific stimulation, resulting in an improved ankle dorsiflexion during the swing phase of gait with its implantable hybrid stimulation system. Further, it showed improved ankle joint kinematics and an increased walking speed compared with surface stimulation 3, 11.

Although the implantation of the ActiGait stimulator is easy and was already roughly described 2, 5, several pitfalls can lead to complications. Currently, complications like hematomas at the side of the cuff placement, postoperative lymphedema at the stimulator body (both occurred in 1 of 5 patients [14]), wound healing disturbance (1 of 15 patients [2], 1 of 27 patients [11]), infections (2 of 15 patients [2]), and nerve injury (2 of 27 patients [11]) are described. After implantation of ActiGait drop foot stimulator in 50 patients, we present the first technical note with possible pitfalls of the surgical procedure and the perioperative care.

Section snippets

ActiGait Drop Foot Stimulator Components

The ActiGait stimulation system (Neurodan/Otto Bock Group, Aalborg, Denmark) consists of an external control unit, a heel switch, and an implantable 4-channel nerve stimulator with a 12-contact electrode cuff (Figure 1). The heel switch, which is worn in a sock, triggers the initiation and termination of each stimulation sequence by a radiofrequency wireless signal to the external control unit when the foot is lifted from the ground. The external control unit can be linked to a personal

Preoperative Requirements

Only patients with a persisting spastic leg paresis as a result of an injury of the central nervous system are suited for the implantation of the drop foot stimulator. Peripheral nerve injuries like diabetic polyneuropathy, ischemic nerve injury, and nerve root impairment are contraindications for the implantation of ActiGait. The best outcome can be achieved when the patient has a retained residual function of the foot elevation (Janda 2/5) and the spasticity is not too marked (<3 according to

Surgical Procedure

Surgery should be performed in general anesthesia in lateral position with the affected side up. The knee wrinkle and tendon of the biceps femoris muscle should be marked for an optimal skin incision. After shaving, disinfection, and draping of the operation region and of the foot (for intraoperative testing of the dorsiflexion), 1 cm medial to the marked tendon an 8-cm incision should be made parallel to the muscle proximal from the knee wrinkle (see Figure 2). The cable that is then planted

Postoperative Care

For the first 5 weeks, the patients should restrict the movement of their operated leg to a maximal knee flexion of 30°. Further, during this time period, the Achilles tendon should be stretched passively to avoid contractures. Afterwards, the programming of the system can be started. First, every channel should be tested for the best dorsiflexion. Further, the stimulator may be activated with 1 mA, 20–30 Hz, and optimal impulse duration of 70 μsec. Finally, the patient will be able to readjust

Conclusions

The implantation of the ActiGait peroneal nerve stimulator is easy and uncomplicated when several basic aspects are taken into consideration:

  • A drop foot due to a peripheral nerve injury should be excluded to enable a good clinical outcome.

  • An exact planning of the position of the implants is essential to ensure a comfortable handling of the device by the patients.

  • Intraoperative electrophysiological testing should be performed to avoid an inadvertent implantation of the cuff electrode around the

References (16)

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Both K. Daniel Martin and Witold Polanski contributed equally to this work.

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