Implementation, Testing and Clinical Evaluation of New Therapeutic Splints Based On the Pseudoelastic Properties of NiTi and NiTiNb

Pseudoelastic alloys can be efficient in providing corrective forces to promote repositioning of paretic limbs. The ongoing PARS&C project aims at demonstrating that a customized choice of alloy composition, thermo-mechanical treatment and shaping can produce effective instruments applicable to sub-acute and chronic spastic paresis in post-traumatic paediatric patients. Two special box hinges were designed and constructed to contain the SMA element and transfer pseudoelastic recovery force to fitted splints for the elbow or the ankle joint. The hinges for the two different anatomical joints have slightly different construction details so that the range of rotation, the preload angle and the external  interfaces adapt to the physiological requirements. The SMA element is given the shape of a capital Ω to create a flexion spring that can be loaded very uniformly and produce large angular strokes and quasi-constant torques. Both types of devices were mechanically tested at room temperature and show complete stability after 20 to 100 cycles and unchanged characteristics after 1000 full-range deflections. The properties of these hinges are important in order to provide suitable corrective action without hindering residual voluntary or reflex mobility of the affected limb and cause the least possible discomfort to the patient. Pseudoelastic hinged splints mounting NiTi or NiTiNb Ω springs were prescribed to 6 patients (aged 12±5.17 years) with mild to severe spastic tetraparesis as a result of a traumatic brain injury. Clinical and instrumental evaluation was conducted prior to and following a two-step treatment with traditional and pseudoelastic splints. The sequence of treatment steps was randomized. Results obtained so far show that, compared to fixed-angle braces, pseudoelastic devices are more tolerable, safeguard joint flexibility better, can reduce pathological stretch reflexes and spasticity (measured on the Ashworth scale), can increase the range of motion, and improve the resting limb position.