Estimation of carrying angle based on CT images in preoperative surgical planning for cubitus deformities

Conventionally, the carrying angle of the elbow is measured using simple two-dimensional radiography or goniometry, which has questionable reliability. This study proposes a novel method for estimating carrying angles using computed tomography that can enhance the reliability of the angle measurement. Data of CT scans from 25 elbow joints were processed to build segmented three-dimensional models. The cross-sectional centerlines of the ulna and the humerus were traced from the 3D models, and the angle between 2 vectors formed from the centerlines of the humerus and the ulna was defined as the "three-dimensional carrying angle." These angles were compared with those measured by simple radiograph. Two cases of angular deformity were underwent surgery based on this preoperative surgical planning, and the postoperative 3D carrying angles were evaluated using the proposed method. The mean value of the calculated three-dimensional carrying angle was 20.7 degrees +/-3.61, while it was 16.3 degrees +/-3.21 based on simple radiography without statistical difference. Based on the 3D carrying angle estimations, 2 surgical cases of cubitus deformities were planned by comparison with the normal contra-lateral elbow. Postoperative angle estimations confirmed that the corrected angles were nearly identical to the planned angles for both cases. The results of this study showed that the carrying angle can be accurately estimated using three-dimensional CT and that the proposed method is useful in evaluating deformities of the elbow with high reliability.