An analysis method of direction of bone tunnel enlargement in mdct image after anterior cruciate ligament reconstruction

Anterior cruciate ligament (ACL) reconstruction is making a hole called as bone tunnel to fix a graft to the femur and tibia. A volume change of this bone tunnel enlargement with time affects a knee motion. We have already developed three dimensional analysis method for knee july-row detector computed tomography (MDCT) image. However, the direction of the bone tunnel enlargement was unclear, because the conventional method considered only volume change of bone tunnel. Then, the aim of this study is to propose a method to analyze the direction of bone tunnel enlargement. There are two important things for the calculation. The first is to determine the femur coordinate system. Then, the second is to execute registration for unifying the femur coordinate system between different MDCT images. In addition, the bone tunnel was evaluated by dividing three region (i.e., proximal, intermediate, and distal) for specifying a location of the enlargement. In the experiment, MDCT images of five patients (single bundle), and eight patients (double bundle) were acquired with informed consent. As a result, about volume change, distal and proximal region had tendencies of enlargement and reduction, respectively. Then, about gravity point movement, all regions had tendencies of distal movement. The proposed method could determine the tibial bone coordinate system.