Verification of tightening torque of rod fixing parts of ultrasonic growing rod system for spinal fusion

In past research, we have developed a telescopic rod system that expands and contracts inside the human body that can be used for spinal fusion. The system can be expanded and contracted as the wearer grows and changes in symptoms by applying ultrasonic vibration. The telescopic rod system consists of instruments used in actual spinal fusion, special metal rods, and metal nuts. The tightening torque of the locking cap that secures the metal rod to the spine changes the movement of the rod system. In this paper, we show the verification of the effect of tightening torque on the movement of the rod. Verification was performed in water using an ultrasonic probe. From the experimental results, the effect of tightening torque on the outside was quantitatively shown, and the results effective for future development were shown.