Growing Rod System with Automatic Stop Mechanism Under Continuous Vibration Input

Scoliosis is the disease that the spine curves, and that occurs most often during the growth spurt just before puberty. The seriously ill patient undergoes surgery on the spine that the pedicle screws and the rod are implanted in. And the surgery is repeated until the growing up stops to adjust the rod. To decrease the physical and psychic load of the surgical operation, we have studied and developed the growing rod system using an ultrasonic vibration. The automatic stop mechanism for the guarantee of the safety is necessary to adapt the system for the home care. In this paper, we confirm that the system includes a mechanism for the automatic stop of the motion of the rod. First, we consider the principle and the relationship between the external force and the amount of movement. Second, it is investigated by the experiments. As a result, it is clear that the system includes a mechanism for the automatic stop, and that the amount of movement is kept small if the unexpected large force. In addition, the feature is not influenced by the vibration point where the external force is applied to the growing rod, even if the point is not same.