The influence of water jet diameter and bone structural properties on the efficiency of pure water jet drilling in porcine bone

Using water jets in orthopedic surgery to drill holes in bones can be beneficial due to the absence of thermal damage and the always sharp cut. To minimize operating time and the volume of water that is used, the efficiency (volume of removed bone per added volume of water) of the water jet should be maximized. The goal was to study the effect of the open trabecular bone structure on the efficiency for different water jet diameters. 86 holes were drilled in porcine tali and femora submerged in water with nozzles of 0.3, 0.4, 0.5 and 0.6 mm at 70 MPa during 5 s and a standoff distance of 8 mm. MicroCT scans were made to measure the removed bone volume and the bone structural properties Trabecular Spacing (Tb. Sp.), Trabecular Thickness (Tb. Sp.) and Bone Volume Fraction (BV/TV). Pearson's correlation tests (p < 0.05, 95% confidence interval) were performed for each water jet diameter using the bone structural property as an independent factor and the efficiency as a dependent factor. No significant differences were found between the nozzle diameters in the material removal rates per added volume of water. The efficiency decreased for an increase in Tb. Th. and BV/TV for nozzles of 0.3, 0.4 and 0.5 mm. The 0.6 mm nozzle showed less influence of the Tb. Th. and BV/TV. The Tb. Sp. has no influence on the efficiency of a water jet. The total volume of added water combined with the Tb. Th. or BV/TV is a leading measure for the volume of bone material that is removed, which provides freedom in the development of water jet instruments as the nozzle diameter, pressure and jet time can be chosen in accordance to the maximum operating time requirements or dimensional limitations of a design.