Comparison of two methods for subpubic angle measurement from reconstructed three-dimensional pelvic model

Background Sex estimation using the subpubic angle of the pelvis is highly accurate for identification of unknown skeletonized remains. This study compared two methods for measuring the subpubic angle from reconstructed three-dimensional (3D) pelvic models. The aims were to quantify the differences in the subpubic angle measurement by Checkpoint (Method 1) and MeshLab + OnScreenProtractor (Method 2), to determine the 95% limits of agreement and to identify any measurement bias. Multislice computed tomography (MSCT) scans of 85 individuals were used in this study. The MSCT scans were performed on a Siemens SOMATOM Sensation 64 scanner (Siemens Germany Ltd.). Segmentation of the MSCT scans was performed using 3D Slicer to reconstruct 3D pelvic models. Subpubic angle was measured on Checkpoint using four landmarks (Method 1), and with OnScreenProtractor on MeshLab (Method 2). Results The intraclass correlation coefficient (ICC) showed a high correlation between repeated measurements in both methods. Subpubic angle measurements by Method 1 and Method 2 were significantly different (p < 0.05). Method 2 (M = 82.2 degrees, SD = 13.5 degrees), consistently showed a larger subpubic angle measurement than Method 1 (M = 77.3 degrees, SD = 12.3 degrees) (consistent bias). More than 95% of the differences (82/85) between Checkpoint and MeshLab fell within the 95% limits of agreement (- 1.4 degrees and 11.4 degrees). Conclusion Checkpoint and MeshLab displayed significantly different subpubic angle measurement on a 3D pelvic model, but within the 95% limits of agreement. The MeshLab tended to give a larger measurement (5 degrees), across the magnitude of the subpubic angle. The decision to use the two methods interchangeably depended on the clinical judgment of the observer.