Three-Dimensional Spatial Location Method Using Intraoperative X-ray Image for Distal Holes of Intramedullary Nails

In the repair of human long bone fracture, the intramedullary nail needs to be inserted into the medullary cavity in order to fix the fracture area. Afterwards, the screw needs to be placed into the distal hole to fix the intramedullary nail. The difficulty is that the distal hole posture will change with the shape of medullary cavity. Therefore, it is difficult to target the distal hole with the matching aiming instrument. At present, the success rate of this operation is only 30%, and the error needs to be controlled within 2mm. Based on two intraoperative X-ray images at different angles, a method to accurately locate the distal hole is proposed through deep feature extraction and deep regression of the hole axis. Firstly, the nail's contour is extracted by the object detection algorithm, and the deep neural network is used to predict the projection of the hole's axis in the imaging plane. Then, the 3D axis posture of the distal hole is preliminarily determined according to the dual-plane intersection. Finally, using the contour information of the nail, the CMA-ES (Covariance Matrix Adaptation Evolutionary Strategies) algorithm is used for pose iterative correction. The experiments are carried out in the simulated and clinical environments, and the distal hole's axis calculated by this method is compared with the real hole's axis. In the simulated environment, the average distance error is 0.34 mm, and the average angle error is 0.35°. Furthermore, the clinical experimental results show that the average distance error is 0.68 mm, and the average angle error is 0.72°. The method can meet the actual surgical needs of distal hole location; and improves the efficiency of location and planning in the distal locking nail surgery.