Intraosseous monitoring and guiding by ultrasound: a feasibility study

An efficient method for navigation within bone tissue boundaries is essential for performance of surgical procedures, e.g. without damaging of adjacent vulnerable organs. The application of sonographic measuring methods for this purpose promises to be effective in the ability to distinguish soft trabecular bone from dense cortical bone, owing to an order of magnitude difference in acoustic density between these structures. For this purpose, a specific method was developed that utilizes propagation of a 5 MHz ultrasonic wave through an aqueous milieu. Using this method a 0.2mm resolution in measurements is achieved. This resolution is in an order of magnitude lower than is required for a clinical use. A three-stage experimental approach was adopted: measurements in a cubic "phantom" made of a transparent plastic material, in samples of fresh porcine femora, and in a clinical setting of drilling in the upper and lower jaw during dental implantation surgery in nine patients. Two patterns of the detected ultrasound wave reflections were found: low amplitude reflections from the aqueous surrounding and trabecular bone and highly reflected ultrasound waves from the cortical bone. We show that trabecular and cortical bones are distinguishable by real-time ultrasonic measurement. The distances of the drilled tracts, in the range of 58.0-122.0 mm for the "phantom" experiment, 22.6-35.5 mm for the ex vivo experiment and 10.0-11.5 mm in the clinical experiment, and residual distances to the opposite edge of the tested samples and organs, in the range of 21.0-82.0 mm for the "phantom" experiment, 3.8-11.36 mm for the ex vivo experiment and 2.1-6.9 mm in the clinical experiment, were measured by the presented sonographic method and compared statistically, using linear correlation and Bland Altman plot, to the mechanical and/or radiographic measurements in all three stages of the experiment. A correlation coefficient above 0.95 was considered an indication of high correlation, while a value of 0.75-0.94 was considered intermediate, and a value below 0.75 was considered poor. A very high correlation (p < 0.001) and agreement between the sonographic and the "gold standard" measurements techniques, either mechanical or radiographic depending on the experimental setting, were found. Therefore the presented method of intraosseous sonographic measurements may provide an improved method for the monitoring of intraosseous drilling in respect of the currently used mechanical and/or radiographic clinical methods.