Cutting characteristics of ultrasonic surgical instruments

Objective: Ultrasonic surgical devices are becoming increasingly popular and work is required to understand the performance of the cutting tips. This experimental study looks to investigate the way in which ultrasonic bone cutting tools oscillate and how this oscillation is modified when contacted against bone surfaces with varying loads. The defects produced in instrumented bone surfaces were measured and related to the tip motion. Methods: An ultrasonic cutting probe was scanned, unloaded, using a scanning laser vibrometer to determine its free oscillation pattern and amplitude. This probe tip was then contacted against bone under various loads to assess the modification in oscillation characteristics. Cuts were performed over a period of 10s. The cut bone surfaces were assessed using laser profilometry to determine defect depths. Results: The average vibration displacement amplitude at the probe tip, under load, was <12 mu m in the longitudinal direction and was greatest for the cortical cutting mode. Elliptical probe motion was successfully mapped out under the range of loads tested. Defect depths of up to 0.36mm were detected and were greatest when the tip was in contact with the bone with a load of 100 g. Conclusions: This work showed that the nature of the surface being cut may significantly alter the mode shape and magnitude of the probe oscillation. The maximum depth of cut with minimum restraining of tip motion was achieved at 100 g contact load.