Accuracy of CT for measuring femoral neck anteversion in children with developmental dislocation of the hip verified using 3D printing technology

Abstract

Background: Accurate femoral neck anteversion angle (FNA) measurement is of great significance in the diagnosis and treatment of developmental dysplasia of the hip (DDH) in children. The FNA measurement still remains a controversy. We aimed to verify the accuracy of our CT method by 3D printing technology and to evaluate its clinical value.

Methods: Sixty-eight children with unilateral DDH were enrolled, and their FNA was measured using 2D-CT and 3D-CT, respectively, by three observers. This procedure was repeated 3 months later. The above measurement outcomes were then compared with the results in the 3D-printed femur (3D-PF) model. The FNA in the 3D-PF model was measured by three observers (two radiologists and one orthopedist; all were professors) collectively through electronic angle instrument.

Results: The primary measurement of FNA at the affected hips by 2D-CT was 44.0 ± 6.1, 49.5 ± 8.9, and 52.8 ± 7.9°, respectively. On the 3D-CT, it was 47.6 ± 5.4, 49.3 ± 6.8, and 48.6 ± 6.2°. Three months later, the FNA on 2D-CT was 49.3 ± 10.5, 42.8 ± 7.4, and 45.1 ± 9.3°, and it was 48.0 ± 6.5, 48.9 ± 7.2, and 49.0 ± 5.7° on 3D-CT, respectively. The FNA in the 3D-PF model at the affected and unaffected hips was 48.5 ± 6.6 and 36.9 ± 13.1°. There were significant differences between 2D-CT and 3D-PF measurements, but no significant difference was found between 3D-CT and 3D-PF measurements. The results by 2D-CT showed significant differences among groups and between the groups. However, the results by 3D-CT had no significant differences among groups or between the groups.

Conclusion: The results of our study showed that 3D-CT is a more precise, and reproducible method for FNA measurement in DDH. The FNA at the affected hips is 11.6° larger than the unaffected in DDH children aged 3-8 years.

Keywords: 3D printing technology; Anteversion angle; CT measurement; Femoral neck; Hip joint.

Fig. 1

2D-FNA. a CT image of the femoral head and the femoral neck. The center of the femoral head and the femoral neck is connected to determine the femoral head-neck axis. b It shows the largest layer of the two femoral condyles; the points of A and B are the tangent of the posterior rim of the two condyles. The angle between the femoral head-neck axis and the tangent is 2D-FNA

Fig. 2

3D-FNA. a CT-reconstruction image of the pelvis and the distal and proximal femur. b 3D-FNA: the lowest point of the greater trochanter and the medial and lateral femoral condyles are located on a horizontal line by rotating the image. The angle between this horizontal line and the femoral neck axis is the 3D-FNA

Fig. 3

3D PF-FNA. The lowest point of the greater trochanter on the 3D-PF model is located on the same horizontal plane as the medial and lateral condyles of the femur. The center of the femoral head and neck is positioned with a vernier caliper. The angle between these two points and the horizontal plane is measured by electronic angle instrument (called 3DPF-FNA)

Fig. 4

Bland-Altman analysis of different measurements. a Compared with the value measured by 2D-CT and 3D-CT, the maximum difference is 15.87 and the mean is 47.06. The results of the two methods are inconsistent. b Compared with the value measured by 2D-CT and 3D-PF, the maximum difference is 16.96 and the mean is 47.28. The results of the two methods are inconsistent. Compared with the value measured by 3D-CT and 3D-PF, the maximum difference is 1.39, and the mean is 48.71. The results of the two methods have high consistency