Passive ankle dorsiflexion by an automated device and the reactivity of the motor cortical network.

Gait impairment is an important consequence of neurological disease. Passive mobilization of the affected lower limbs is often prescribed in order to safeguard tissue properties and prevent circulatory sequelae during paresis. However, passive movement could play a role also in stimulating cortical areas of the brain devoted to the control of the lower limb, so that deafferentation and learned non-use can be contrasted. The purpose of the present work is to investigate cortical involvement during active and passive movements of the ankle joint, in an attempt to gain deeper insight in the similarities between these two conditions. A wearable device to mobilize the ankle joint was implemented utilizing rotary shape memory alloy actuators. The technical characteristics of this actuator make it very compatible with the tight limitations on electromagnetic noise imposed by diagnostic instrumentation. Eleven healthy volunteers took part in the pre-clinical phase of the study. According to the protocol, brain activity was recorded by 165-channel magnetoencephalography (MEG) under three different conditions: rest, active dorsiflexion of the ankle and passive mobilization of the same joint. The acquired data were processed to obtain cortical ERD/ERS (Event Related Desynchronization/ Synchronization) maps, which were then compared. The results of this analysis show that there are similar patterns of activity between active and passive movement, particularly in ß band, in the contralateral primary sensorimotor, dorsal premotor and supplementary motor areas. This result, albeit obtained from healthy subjects, might suggest that passive motion provides somatosensory afferences that, to some extent, are processed in a similar manner as for voluntary control. Should this evidence be confirmed by further experiments on neurological patients, it could support the prescription of passive exercise as a surrogate of active workout, at least, so long as patients are paretic.

Primary sensory and motor cortex activities during voluntary and passive ankle mobilization by the SHADE orthosis.

This study investigates cortical involvement during ankle passive mobilization in healthy subjects, and is part of a pilot study on stroke patient rehabilitation. Magnetoencephalographic signals from the primary sensorimotor areas devoted to the lower limb were collected together with simultaneous electromyographic activities from tibialis anterior (TA). This was done bilaterally, on seven healthy subjects (aged 29 ± 7), during rest, left and right passive ankle dorsiflexion (imparted through the SHADE orthosis, O-PM, or neuromuscular electrical stimulation, NMES-PM), and during active isometric contraction (IC-AM). The effects of focussing attention on ankle passive movements were considered. Primary sensory (FS(S1)) and motor (FS(M1)) area activities were discriminated by the Functional Source Separation algorithm. Only contralateral FS(S1) was recruited by common peroneal nerve stimulation and only contralateral FS(M1) displayed coherence with TA muscular activity. FS(M1) showed higher power of gamma rhythms (33-90 Hz) than FS(S1). Both sources displayed higher beta (14-32 Hz) and gamma powers in the left than in the right hemisphere. Both sources displayed a bilateral reduction of beta power during IC-AM with respect to rest. Only FS(S1) beta band power reduced during O-PM. No beta band modulation was observed of either source during NMES-PM. Mutual FS(S1)-FS(M1) coherence in gamma2 band (61-90 Hz) showed a slight trend towards an increase when focussing attention during O-PM. Somatosensory and motor counterparts of lower limb cortical representations were discriminated in both hemispheres. SHADE was effective in generating repeatable dorsiflexion and inducing primary sensory involvement similarly to voluntary movement.

Pilot studies suggesting new applications of NiTi in dynamic orthoses for the ankle joint.

NiTi is a metal alloy with unconventional functional characteristics: Shape memory and pseudoelasticity. Its use in the field of rehabilitation is very innovative. This work presents applications in lower limb orthotics. Three different devices were assembled and tested: An equinus gait dynamic splint, a compliant ankle positioning brace, and a dual-mode haptic/active exerciser for the dorsiflexors. Results are derived from technical and preclinical trials. The gait splint improves several walking parameters even better than a traditional flexible ankle-foot orthoses (AFO). In particular, it supports mid-stance and propulsion biomechanics and affects physiological activation of tibialis anterior during swing much less than posterior leaf AFO. The haptic/active exerciser, able to provide dorsiflexion through a suitable articular range, could be controlled on the basis of minimal surface electromyographic (sEMG) signals, suggesting its use as an aid for early active workouts as soon as patients start to recover voluntary control of tibialis anterior. Further evidence must be sought in future to confirm for the ankle joint the promising results obtained in repositioning applications in prior upper limb studies. The work done so far on the tested prototypes is encouraging: Material characteristics and dimensioning will be optimized so that customized NiTi devices can be prescribed to best meet individual patients' requirements.