A novel parameter decomposition based optimization approach for automatic pose estimation of distal locking holes from single calibrated fluoroscopic image

One of the most difficult steps in intramedullary nailing of femoral shaft fractures is distal locking – the insertion of distal transverse interlocking screws, for which it is necessary to know the positions and the orientations of the distal locking holes of the intramedullary nail (IMN). This paper presents a novel parameter decomposition based optimization approach for solving this problem using single calibrated X-ray image. The problem is formulated as a model-based optimal fitting process, where the to-be-optimized parameters are decomposed into two sets: (a) the angle between the nail axis and its projection in the imaging plane, and (b) the translation and the rotation of the geometrical models of the distal locking holes around the nail axis. By using a hybrid optimization technique coupling an evolutionary strategy and a local search algorithm to find the optimal values of the latter set of parameters for any given value of the former one, we reduce the multiple-dimensional model-based optimal fitting problem to an one-dimensional search along a finite interval. We report the results of our comprehensive experiments, which demonstrate that the accuracy of our approach is adequate for successful distal locking of intramedullary nails.