Utilizing Flexible Magnetic-Alloy Sheet with Rolling-to-Attaching Method to Fabricate a Smart Nail for Electromagnetic Screw-Hole Targeting in Intramedullary Interlocking-Nail Surgery

In this paper, we present a novel method to fabricate a smart nail for electromagnetic targeting of distal screw-holes in intramedullary interlocking-nail surgery. The nail is fabricated by using a flexible magnetic-alloy Metglas sheet with a rolling-to-attaching method. That is, among most high permeable magnetic materials, the Metglas sheet has superior features in flexibility and bendability and therefore can be rolled and inserted inside the nail to accordingly conform to curvature of inner surface of the nail. Regarding the targeting system, we used a conventional c-shaped electromagnet (consisting of a c-shaped silicon steel core, emitting coil, and receiving coil) with measurement electronics as the targeting system. At first, an AC input voltage is applied to the emitting coil to generate magnetic flux in the air-gap between emitting coil and receiving coil. Consequently, by electromagnetic induction, an AC voltage is induced in the receiving coil. As the nail is axially moved or rotated within the air-gap between the emitting and receiving coils, the magnetic flux between the coils is influenced, leading to a change in the voltage output of the receiving coil. This voltage change is further analyzed to determine location and orientation of the Metglas sheet (as well as screw holes). Based on this targeting principle, we conduct location and orientation targeting tests. Results show that our method not only can successfully achieve these targeting, but also significantly simplifies the complexity of both targeting system and surgical procedure, in practical perspective.