Towards physiological ankle movements with the ActiGait implantable drop foot stimulator in chronic stroke

Purpose: Functional electrical stimulation represents an alternative to conventional and passive ankle foot orthosis (AFO) for the treatment of stroke-related drop foot. We evaluated the implantable 4-channel stimulator ActiGait, which selectively and directly stimulates the peroneal nerve. In addition, it bypasses the need for surface electrodes and cables. Methods: Walking speed (10-meter gait test, [m/s]) and walking endurance (6-minute gait test [m/6min]) of 5 patients were tested prior to, as well as 6 and 12 weeks after, the implantation of the ActiGait implantable drop foot stimulator system. In addition, ankle joint angles were assessed during specific phases of the gait cycle, i.e. initiation angle (IA) at the first contact of the foot to the floor, initial plantar flexion (IPF), dorsiflexion (DF) and final plantar flexion (FPF) in [degrees] during stance phase. The ankle joint angles were measured at baseline and 12 weeks after ActiGait implantation. Results: At the first follow-up, patients' gait speed was found to have increased (0.55; 0.77 m/s) as had walking endurance (211; 260 m). Improvement in gait speed (0.55; 0.77 m/s) and endurance (214; 248 m) was still present after 12 weeks. In addition, gait analysis after 12 weeks revealed a nearly normal physiological initiation angle (113 degrees vs 122 degrees) and an increase in the initial plantar flexion (7 degrees vs. 0 degrees). The initiation angle (IA) represents a well-suited parameter for adequate pre-positioning of the foot at the beginning of the stance phase and is necessary to prevent stumbling and falling. Furthermore, IA is identical to the maximum achieved dorsiflexion during the swing phase of gait. Thus, analysis of the IA of subjects walking with the implantable drop foot stimulator systems ActiGait is particularly useful in showing that the implantable system restores the IA towards physiological ankle movements. Conclusion: The ActiGait system increased gait speed, walking endurance and the physiology of important ankle joint kinematics. This is most likely a result of ankle dorsiflexion by active peroneal stimulation during the swing phase of gait and optimized prepositioning (IA) of the foot at the beginning of stance phase. The ActiGait system represents a therapeutic option for the treatment of patients suffering drop foot due to a cerebrovascular insult.