Can Computed Tomography Accurately Measure Acetabular Anterversion in Developmental Dysplasia of the Hip? Verification and Characterization Using 3D Printing Technology

BACKGROUND: One of the important pathologic changes in developmental dysplasia of the hip (DDH) is increased acetabular version angle (AA). Reasonable correction for excessive AA is an important step in the treatment of DDH, making accurate AA measurement very crucial. However, the results of different AA measurement methods vary. Thus, this study aimed to compare the difference in AA measurements between 2-dimensional computed tomography (2D-CT) and 3-dimensional computed tomography (3D-CT) in children with DDH and to identify the AA degree in children with DDH to guide treatment. METHODS: AA was measured by 2D-CT and 3D-CT in 186 children with DDH, and the measurement results were compared with the physical measurement result in the 3D-printed pelvis (3D-PP) model. The 3D-PP was a 1:1 model identical to the human pelvis. All patients were unilaterally affected. RESULTS: The results of AA measurement through 2D-CT, 3D-CT, and 3D-PP of normal hips were 14.0±6.6, 11.9±5.3, and 11.9±3.4 degrees, respectively, whereas those of the dislocated hips were 24.9±8.9, 19.8±5.2, and 19.5±4.3 degrees, respectively. In both the normal and dislocated hip groups, the results between 2D-CT and 3D-CT was significantly different (P 0.05). The AA of the normal and dislocated hips as measured by 3D-PP was 11.9±3.6 and 19.6±4.3 degrees, respectively, with statistically significant difference (P<0.05). In the dislocated hips, a significant positive correlation was found between age and AA (r=0.756, P<0.05) and between AA and degree of dislocation (r=0.837, P<0.05). CONCLUSIONS: 3D-CT is more accurate than 2D-CT for AA measurement, and compared with normal hips, AA in dislocated hips increased by ∼7.7 degrees on average. AA increases as age and degree of dislocation increase. LEVEL OF EVIDENCE: Level II.