Development of an ultrasonic controlled growing rod system for spinal implants
An ultrasonic controlled growing rod system for scoliosis spinal implants is proposed for the correction of an abnormal lateral rotated curvature of the spine of adolescents during growth period. The proposed system comprises a growing rod with screw threads on both ends wherein the rotation is in the opposite direction, a vibrated and deformed nut driven by ultrasonic excitation and the resonance plates attached to the nut. The shape of the screw thread on the nut is discrete and asymmetrical. Using resonance phenomena, the nut drives a screw on the rod. When the excitation position changes, the vibration mode and rotation direction of a nut also change. To maintain compatibility with conventional spinal implants, pedicle screws for spinal stabilization with a conventional shape, are used for fixation. The simulation results confirm that the driving nut deforms periodically using ultrasonic excitation during the estimated vibration mode. The prototype is tested under direct contact condition for a non-biomedical condition, and the results confirm that the prototype delivers satisfactory results owing to its sufficient extension and contraction performance.
KeywordsScoliosis Spinal implant Ultrasonic Growing rod Driving nut
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This work was supported by the JSPS KAKENHI Grant Number JP17K13043.
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