Hydraulic pressure wave bone drilling

Abstract

Spinal fusion surgery is applied, amongst other reasons, to correct unwanted curves in a spine hampered by scoliosis. During spinal fusion surgery, holes in the vertebra must be drilled, after which pedicle screws are placed. Traditional drilling only allows for the formation of straight holes. Ill-placed trajectories cannot be course-corrected, leading to repositioning the drill and starting again in the, weakened by the first attempt, vertebra. This thesis aims to develop a drilling method that will allow for the application of trajectory control during operation. This will form the first step towards a new spinal surgical instrument that could be used for course-correcting during spinal drilling or form curved holes applicable for new state-of-the-art alternate bone anchors.
The proof-of-principle instrument designed and fabricated in this thesis consists of an impulse generation part, a bendable tube with a saline medium, and a working head, which will perform the impacts on the bone tissue. The method consists of drilling using the repetitive impact of a solid round tip with a diameter of 4 mm. Through the use of a bendable impulse transmission tube, the instrument allows for the application of steerable drilling. The impulse will be generated by a manual compressed and released compression spring. This impulse will be translated into a hydraulic pressure wave; whereafter it will travel through the liquid medium of the tube, ending at the working head, which translates it into an impact on the target tissue.
The method has been proven to work in every state of curvature of the transmitting tube, ranging from 0 degrees till 90 degrees. Furthermore, almost 20% of the desired impulse output found in this thesis, 0.077 Ns, that would allow for high-speed drilling, 0.3 mm per strike, was reached. A linear increase in impulse output was found, correlating with the linear input increase, suggesting plausible higher impulse output magnitudes could be possible. In the future, the instrument's efficiency should be increased, as a mean efficiency of 3.5% was achieved, caused mainly by leakage of the saline filler and high friction with the mechanisms in the tube. All in all, the method shows great potential to be utilised as a future trajectory controlled bone drilling instrument.