Kinematic and kinetic benefits of implantable peroneal nerve stimulation in people with post-stroke drop foot using an ankle-foot orthosis

BACKGROUND: Contralesional 'drop foot' after stroke is usually treated with an ankle-foot orthosis (AFO). However, AFOs may hamper ankle motion during stance. Peroneal functional electrical stimulation (FES) is an alternative treatment that provides active dorsiflexion and allows normal ankle motion. Despite this theoretical advantage of FES, the kinematic and kinetic differences between AFO and FES have been scarcely investigated.

OBJECTIVE: To test whether walking with implanted FES leads to improvements in stance stability, propulsion, and swing initiation compared to AFO.

METHODS: A 4-channel peroneal nerve stimulator (ActiGait ®) was implanted in 22 chronic patients after stroke. Instrumented gait analyses were performed during comfortable walking up to 26 weeks (n = 10) or 52 weeks (n = 12) after FES-system activation. Kinematics of knee and ankle (stance and swing phase) and kinetics (stance phase) of gait were determined, besides spatiotemporal parameters. Finally, we determined whether differences between devices regarding late stance kine(ma)tics correlated with those regarding the swing phase.

RESULTS: In mid-stance, knee stability improved as the peak knee extension velocity was lower with FES (β = 18.1°/s, p = 0.007), while peak ankle plantarflexion velocity (β = -29.2°/s, p = 0.006) and peak ankle plantarflexion power (β = -0.2 W/kg, p = 0.018) were higher with FES compared to AFO. With FES, the ground reaction force (GRF) vector at peak ankle power (i.e., 'propulsion') was oriented more anteriorly (β = -1.1°, p = 0.001). Similarly, the horizontal GRF (β = -0.8% body mass, p = 0.003) and gait speed (β = 0.03 m/s, p = 0.015) were higher. An increase in peak ankle plantarflexion velocity and a more forward oriented GRF angle during late stance were moderately associated with an increase in hip flexion velocity during initial swing (rs = 0.502, p = 0.029 and rs = 0.504, p = 0.028, respectively).

CONCLUSIONS: This study substantiates the evidence that implantable peroneal FES as a treatment for post-stroke drop foot may be superior over AFO in terms of knee stability, ankle plantarflexion power, and propulsion.