Development of a “steerable drill” for ACL reconstruction to create the arbitrary trajectory of a bone tunnel

It is often difficult for orthopedic surgeons to avoid LCL injury during ACL reconstruction. In this paper, we developed a steerable drill for ACL reconstruction to avoid LCL injury in the process of making a bone tunnel. There are two special requirements for the steerable drill mechanism. One is having sufficient flexibility to bend and avoid LCL while cutting the bone. The other is rigidity to avoid the buckle at the base of the drill when external force is exerted on the drill tip. These two requirements cannot be met simultaneously by using the previous material with uniform stiffness throughout its length. We therefore adopted a spring sheath with stiffness that varied between the top and base of the drill. This spring sheath has high stiffness at the base and low stiffness at the top. We performed the experiment to evaluate the effectiveness of the drill with uniform and non-uniform stiffness by comparing each result. Consequently, it was confirmed that the drill with non-uniform stiffness achieved 6 times the bending deformation and with 30% lower force as preventing the buckling compared to the drill with uniform stiffness. Subsequently, we presented a discussion concerning the reason for the experimental result, based on a physical long column model which simulated the steerable drill. In addition, at the end of this paper, a newly-developed control method to make the arbitrary trajectory of the bone tunnel using a steerable drill with non-uniform stiffness was described.