Calibration of X-ray radiographs and its feasible application for 2D/3D reconstruction of the proximal femur

In the past ten years, a variety of computer-assisted surgical technologies have been introduced for total hip replacement (THR). Despite the different approaches, orthopedic surgeons routinely still acquire 2D X-ray radiographs for preoperative diagnostic and templating purposes. Such images provide detailed information in high resolution about the underlying anatomy. But lack of knowledge about the magnification factor of the bony structures complicates the correct interpretation of the real anatomy and therefore could lead to mismatching implants intraoperatively based on the preoperative performed planning. Therefore we developed a calibration device, which can be mounted within the usual clinical environment and allows to improve the accuracy of conventional radiographs by applying a specific calibration algorithm. Furthermore, we investigated the feasibility of reconstructing the surface of the proximal femur on the basis of two calibrated X-ray radiographs. The accuracy of this approach has been thoroughly validated using 14 dry cadaver femur bones (pathological as well as non-pathological cases), one plastic femur bone and one wet cadaver pelvis.