Experimental and Finite Element Analysis of Force and Temperature in Ultrasonic Vibration Assisted Bone Cutting.

Bone cutting is an essential procedure of orthopedic surgery, while irreversible bone damage would be inevitably caused using the conventional cutting (CC) method. In this study, an ultrasonic vibration-assisted cutting (UVAC) method was applied in bone cutting to investigate the cutting performance, considering the cutting force and temperature rise, in comparison with CC. In addition, a finite element (FE) model was developed to investigate the cutting mechanism and the influence of a wide range of processing parameters on the performance of cutting bone. The results indicate that the proposed FE model shows good correlation with the experimental results for both cutting force and temperature. UVAC can significantly reduce the cutting force and increase the temperature in comparison with CC from the experimental and predicted results. The cutting force tends to decrease with the increasing vibrational parameters and decreasing cutting speed, while the temperature increases. The verified FE bone cutting model provides an efficient way to assist the optimization of the processing conditions in bone cutting operations.

Thermographic assessment of heat-induced cellular damage during orthopedic surgery.

The heat generated during orthopedic surgery can cause thermal damage to bone cells, leading to cell necrosis, death, and bone resorption. In this study, the drill-exit surface in cortical bone drilling was firstly investigated by infrared thermography to understand the thermal characteristics of bone cutting. In order to mimic the short-term thermal condition of high temperature during surgical cutting, the osteoblasts were exposed to heat shock for short periods of time to investigate the effect of cutting heat on the bone. Necrosis and apoptosis were investigated immediately after heat shock for 2 s, 5 s, and 15 s at 50 °C, 60 °C, 70 °C, and 80 °C, respectively. The cells were then incubated for 4 days at 37 °C and analyzed by fluorescein annexin V-FITC/PI double staining. The temperature and heat-duration were precisely controlled by a novel heating approach. In comparison to the control group (37 °C), immediate necrotic and apoptotic response to heat shock was found in cells exposed to 50 °C for 5 s (11.8%, p<0.05); however, the response was negligible in cells exposed to 50 °C for 2 s. In addition, recovery was found in the group exposed to 50 °C and 60 °C for 2 s (p ≤ 0.05) after incubation for 4 days. Cell damage depends on the magnitude and duration of heat exposure. These findings provide fundamental knowledge for future developments of surgical tool design and cutting methods.