Methods for reducing cutting temperature in ultrasonic cutting of bone.

Ultrasonic cutting is widely used in food processing applications to produce a clean and accurate cut. However, it is yet to be adopted as an instrument of choice in orthopaedic applications, mainly due to the high temperatures that can be generated at the cut site and the consequent requirement to use additional cooling. For example, if cutting temperatures above 55-60 degrees C are reached, particularly for sustained periods, bone necrosis can occur, compromising post-operative recovery. A recent study by the authors has shown that the thermal response in natural materials, such as wood and bone, is affected by the absorption of ultrasonic energy and conduction of heat from the cut site. In this paper the dependency of cutting parameters, such as blade tip vibration velocity, applied load, tuned frequency and coupling contact conditions, on the thermal response are reported and results show that it is possible to maintain cutting temperatures within safety limits by controlling the cutting parameters. A novel cutting blade design is proposed that reduces frictional heat generated at the cut site. Through a series of experimental investigations using fresh bovine femur it is demonstrated that the cutting temperature, and hence thermal damage, can be reduced by selecting appropriate cutting parameters and blade profile.