2014PJH

Development of a movable mechanism for positioning magnet for distal locking in intramedullary nailing surgery

磁力式骨髓內釘定位系統之定位磁鐵置入/取出機構的研發

Intramedullary nailing is a typical surgical operation to repair fractures of long bones. In the surgery, after the nail is inserted into a bone, the screw-holes become invisible for the surgeons. Thus, one key difficulty of the surgery is to accurately locate the invisible screw-holes in order to obtain the drilling position and direction for interlocking screws. Clinically, intramedullary nail may distort during implantation, therefore the guiding mechanism won’t be able to locate the screw-hole accurately. To address this issue, surgeons use conventional X-ray-imaging approaches to locate the drilling position and direction of the screw-holes. However, utilizing the X-ray-imaging approaches, the surgeons, medical teams, and patients are under the radiation exposure. To prevent the radiation exposure, a non-radiation approach is needed. However, most non-radiation approaches locate only the drilling position not both drilling position and direction. Here we have proposed a novel two-stage passive magnetic guiding system to fast and accurately locate the drilling position and direction.

After our development of the proposed position system and improvement with drilling tests, preliminary results are shown to meet the required specifications: for a remote vertical distance ranging from 16 mm to 20 mm, the accuracy in horizontal position and angular direction are within 2.1 mm and 7 degrees, respectively. Also targeting and drilling one screw-hole can be completed within 8 minutes, which verifies the 3D targeting capability of the proposed design.

However, current approach still needs to modify the intramedullary nail in order to place an internal position magnet at the screw hole, and the magnet can not be removed after operation. Therefore, the main objective of this project is to design proper mechanism which can remove the magnet from the nail without modifying the intramedullary nail, as well as the improvement on the position system for this new design. Working items include: (1) Development of a movable mechanism to insert or remove the position magnet into or from and intramedullary nail; (2) drilling tests. It is hoped that, without modifying the existed intramedullary nail, the proposed two-stage passive magnetic positioning system can be more feasible for commercial product.