Investigations into the use of an ultrasonic chisel to cut bone. Part 2: cutting ability

Objectives: Ultrasound may offer a possible alternative to rotary instruments for removing bone. This study was undertaken to analyse in vitro the various factors that influence the cutting of bone by an ultrasonic chisel. Study design: A block of bovine femur was moved in a longitudinal direction under a stationary ultrasonic chisel. The force and depth of the cut was recorded for cutting rates of 28–112 mm/min and with increasing rake angles of 0 to +20°. The pressure exerted by the chisel was recorded for different cutting rates. Results: When the cutting rate increases there is a corresponding increase in the downward force which is followed by a decrease in the force at rates greater than 56 mm/min. The depth of the cut increases up to a rate of 56 mm/min after which it decreases. Both the longitudinal and downward forces do not change when the rake angle changes from 0 to +10°. The downward force decreases when the rake angle increases from +10 to +20°. Conclusions: The bone is cut slowly with the ultrasonic chisel, but this would assist in precision. Where such an instrument is used for cutting bone the clinicians should be aware that both low forces and cutting rates are required, and the instrument should be held at a low rake angle.