Pilot Studies Suggesting New Applications of NiTi in Dynamic Orthoses for the Ankle Joint

Abstract

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.

An EMG-Controlled SMA Device for the Rehabilitation of the Ankle Joint in Post-Acute Stroke

“…This article supports the idea that rehabilitation of gait can start, in selected patients, as early as the acute phase following a neurological insult that caused lower limb paralysis ( Ref 3,4). Moreover, it proposes that by the use of a suitable exercising robot the process of recovery can be continuously sustained from passive mobilization over to voluntary motion.…”

Shape Memory Actuators for Medical Rehabilitation and Neuroscience

“…The authors suggest that pseudoelasticity can be an interesting solution to the disuse and immobility problems during the orthotic repositioning therapies, in that it safeguards residual motor capabilities (voluntary or reflex) and decreases contact pressure by yielding under muscular jerks. They also showed possible advantages of this type of devices for correcting equinus gait [25]. In [26], pseudoelastic NiTi was utilised to remodel deformed auricles.…”

“…Static orthoses are often used to impart these treatments and may be as rigid as castings or partially compliant. Many authors imagined the use of SMA in orthotics as passive components that apply static corrective forces [20][21][22][23][24][25][26][27][28][29][30]. In these applications SMA are mostly employed for their pseudoelastic properties, even though some designs are also based on SME.…”

“…In these applications SMA are mostly employed for their pseudoelastic properties, even though some designs are also based on SME. A series of papers [20][21][22][23][24][25] showed applications of pseudoelastic NiTi for spastic limb repositioning (elbow, ankle). The authors suggest that pseudoelasticity can be an interesting solution to the disuse and immobility problems during the orthotic repositioning therapies, in that it safeguards residual motor capabilities (voluntary or reflex) and decreases contact pressure by yielding under muscular jerks.…”

Challenges in Lower-Limb Orthotic Research

“…A conundrum exists in that single subject research and case studies such as those by Jagadamma et al 8 and Pittaccio et al 9 are perhaps most readily understood by practitioners and therefore the information more readily transferred to clinical practice. Although easier transference of knowledge may occur when case studies mirror clinical encounters, generalizability of results from one case to an entire population cannot be achieved and so these contributions to knowledge are positioned lower in the hierarchy of evidence.…”