Noncontact Vibration Measurement Based Thoracic Spine Condition Monitoring During Pedicle Drilling

In order to prevent possible damage to the spinal cord, blood vessel or other soft tissues, reliable monitoring methods are required to provide valuable information on the condition of the bone being cut. A method is proposed for monitoring thoracic spine conditions via the use of bone vibration signal during pedicle drilling, which is directly recorded by a noncontact laser displacement sensor. The main reason to cause axial vibration of drill bit is analyzed, and the main frequencies composing the vibration signal are integer multiples of spindle frequency. Then, we analyze the vibration feature of cancellous and cortical bone under this harmonic excitation. Wavelet packet transform is performed to extract the crucial characteristic from the measured data to correlate drilling condition. The safe and dangerous drilling operations are discriminated by the comparison of harmonic energy ratio over some characteristic scales. The proposed method is experimentally verified through the drilling operation in porcine spines, and the results are in accordance with the theoretical analysis and then the safety of the drilling operation is improved.