Radiographic reconstruction of lower-extremity bone fragments: a first trial.

Purpose: The correct rotational alignment of the proximal and the distal bone fragments is an essential step in a long-bone deformity correction process. In order to plan the deformity correction, plain radiographs are conventionally used. But as three-dimensional information of the complex situation is not available, the correct amount of rotation can only be approximated. Thus, the objective of this study was to develop a system to assess the rotational relationship between the proximal and distal fragments of a long bone (tibia or femur) based on a set of two calibrated X-ray radiographs.

Methods: In order to robustly determine the rotational relationship of proximal and distal bone fragments, a statistical shape model-based 2D/3D reconstruction approach was employed. The resulting fragment models were used to determine the angle between its anatomical axes and the rotation around its particular axes. Two different studies were performed to evaluate the accuracy of the proposed system.

Results: The accuracy of the complete system was evaluated in terms of major bone axis and in-plane rotational difference. The angle between the anatomical fragment axes could be measured with an average error of 0.33[Formula: see text] ± 0.27[Formula: see text], while an average in-plane rotational error of 2.27[Formula: see text] ± 1.76[Formula: see text]  and 2.67[Formula: see text]  ± 1.80[Formula: see text]  was found for the proximal and distal fragments, respectively. The overall mean surface reconstruction error was 0.81  ± 0.59 mm when the present technique was applied to the tibia and 1.12 ± 0.87 mm when it was applied to the femur.

Conclusions: A new approach for estimating the rotational parameters of long-bone fragments has been proposed. This approach is based on two conventional radiographs and 2D/3D reconstruction technology. It is generally applicable to the alignment of any long-bone fragments and could provide an important means for achieving accurate rotational alignment.