Estimating the Position of Distal Hole in Femur Intramedullary Nails using Nail Mechanical Modeling and Image Data

Intramedullary nailing is a common technique for treatment of femoral shaft fractures. Nail deformation after insertion into the bone, makes the distal hole locking a challenging task for the surgeon. The proximally mounted targeting systems for locating the position of the distal hole become ineffective due to the nail deformation. The previous image-based techniques have often considered the shape of the distal end of the nail only to find the position and direction of the distal hole. The purpose of this study was to evaluate the hypothesis of possibility of locating the position of the distal hole using mechanical modeling and radiography data simultaneously. In the proposed method, according to the nail geometry (length to diameter ratio between 25 and 50), an Euler-Bernoulli beam model is used to simulate the mechanical behavior of the nail and calculate its deformation pattern. Then, by registering the deformation pattern with the sagittal radiography image of the nail, using iterative closest point algorithm, the nail deformation and the position of the distal hole are predicted. In order to evaluate the research hypothesis, a number of experiments were performed on five cadaveric femurs and the predicted and actual positions of the distal hole were compared. Results indicated that by using mechanical modeling and the imaging data of the nail curvature, the position of the distal hole could be predicted with a mean error of 0.84 mm and a maximum error of 1.3 mm. It is expected that by combining the proposed method with the image-based techniques, which make use of the shape data of the hole, a sub-millimeter error in locating the distal hole could be achieved in future.