Design of a Flexible Bone Drill Using a Hydraulic Pressure Wave

Orthopaedic surgery focuses on the musculoskeletal system and often involves drilling through bone for fracture fixation, bone fusion, or tendon repair. Currently, straight rigid bone drills are utilized to create a tunnel through bone. Although these rigid bone drills are relatively easy to use, it would be advantageous to have a bone drill that can deflect to reach challenging areas, minimise damage to surrounding tissue or create better paths for the fixation of bone anchors or tendons. For instance, in spinal fusion surgery, the use of curved paths combined with novel bone anchors could potentially improve the fixation strength of the bone anchors compared to the currently used pedicle screws. Currently, there are no commercial bone drills available that allow the surgeon to adjust the drilling trajectory during the intervention [1]. The design of steerable bone drills is challenging as the required flexibility to create a curved hole compromises the needed buckling resistance to advance the drill through hard material such as bone. The flexible catheter designed by Sakes et al. was able to successfully transfer an impulse that could be used to hammer through calcification in blood vessels [2]. The catheter comprises a flexible fluid-filled tube that is used to transfer the impulse to the distal tip of the catheter to hammer through the occlusion. Although bone has different characteristics and the diameter of a drilled tunnel for pedicle screws (4 mm) is considerably different from the diameter of a catheter, the use of a hydraulic pressure wave could be beneficial, as the use of an impulse increases the buckling resistance while allowing the required bending for the drilling of curved tunnels. Furthermore, there are indications that the use of an impulse lowers the required penetration load due to the damping of the surrounding tissue which acts as a reaction force. The goal of this study was, therefore, to investigate the use of a hydraulic pressure wave to hammer through bone in a flexible bone drill.