Fig 1.
Schematic showing the segmentation, modeling, and 3D measurement of acetabular orientation.
(A), (B), (C) Points (yellow) were manually located at the joint space on axial and coronal sections of CT images to isolate the femoral head from the pelvis in (A), and then expanded computationally to produce the yellow areas shown in (B) and (C). Spherical masks (gray) are shown on the transverse and coronal planes. (D) A red spherical mask was created by a novel algorithm. A virtual pelvic model (yellow) was reconstructed using threshold and region-growing algorithms. Four initial landmarks were manually located on the bilateral anterior superior iliac spines and pubic tubercles (dots). (E) About 20 points (white) were manually located on the acetabular rim. (F) A B-spline path (green) was built as the rim path using cubic interpolation. The acetabular opening circle and axis were created subsequently. A best-fit circle (blue mesh) was created with a least-squares method. The center of rotation (green sphere) and the axis perpendicular to the opening plane (red line) were computed.
Fig 2.
Establishment of a reliable coordinate system.
By manually identifying anterior superior iliac spines and pubic tubercles, a larger area defined as a point cloud (pink) was automatically selected, and the midsagittal pelvic plane (red) was computed from these points using an iterative closest-point algorithm.
Fig 3.
Schematic showing the pelvic coordinate system and the angular definitions of acetabular orientation.
(Top) The anterior pelvic plane (APP; green) is determined by the bilateral anterior superior iliac spines and the midpoint of the pubic tubercles. The midsagittal plane (MSP; red) is the mirror plane determined by both ASIS regions using an iterative closest-point algorithm. The transverse pelvic plane (TPP; blue), is a plane perpendicular to both APP and MSP, at the level of the ASISs. (Bottom) Standard measures of anteversion (red) and inclination (blue) of the acetabular axis (yellow arrow) on the right acetabulum, showing operative anteversion (OA) and inclination (OI) (left), anatomic anteversion (AA) and inclination (AI) (middle), and radiographic anteversion (RA) and inclination (RI) (right).
Fig 4.
Standardized, simplified 3D virtual pelvic models were created using SOLIDWORKS™ 2015 software (Dassault Systemes, Waltham, Massachusetts) and imported into 3D Acetabulometer as the true (predetermined) value of the 3D orientation, for comparison with the value measured with the algorithm.
Table 1.
Single-measure interobserver reliability.
Table 2.
Single-measure intraobserver reliability.
Table 3.
Difference between the pelvic coordinate system and the global system.
Table 4.
Comparison between males and females.
Fig 5.
Frequency and magnitude of intrapatient bilateral differences (left minus right).
(A) For anatomic anteversion, showing relative symmetry. (B) For anatomic inclination, showing relative symmetry.
Table 5.
Comparison between our study and Higgins et al.'s study.