The online version of this article (doi:10.1186/s12891-015-0503-8) contains supplementary material, which is available to authorized users.
The authors declare that they have no competing interests.
MJ proposed the research idea and took part in creation of the research design and formation of the study methodology, supervised acquisition of data, revised the statistical data, participated in interpretation of results, and drafted the manuscript. MR took part in creation of the research design and formation of the study methodology, carried out the 3D reconstructions of the pelvis and 3D measurements, took part in interpretation of results, and revised the manuscript critically. BM took part in formation of the study methodology, searched the literature, carried out measurements in 3D reconstructions and 2D scans, prepared data for statistics, carried out a statistical analysis, participated in interpretation of results, and drafted the manuscript. AG took part in creation of the research design, formation of the study methodology, and interpretation of results, and revised the manuscript critically. PJC took part in formation of the study methodology, searched the literature, carried out the measurements in 2D scans, prepared data for statistics, and drafted the manuscript. MI took part in formation of the study methodology, searched the literature, carried out a statistical analysis, and drafted the manuscript. All authors read and approved the final manuscript.
Two-dimensional (2D) measurements of acetabular morphology and orientation are well known; there is less information on these acetabular characteristics in three dimensions. One important reason is the lack of standardized reference planes for the pelvis, especially in relation to the spinopelvic unit; another is that no method precisely assesses the acetabulum in three-dimensional (3D) orientation based on its axis rather than on the directions of the edges of the acetabular rim. We present an objective, highly reliable and accurate, axis-based approach to acetabular anthropometry in the measurement of acetabular volume and spatial orientation in both normal and pathologic hips. This was done using reference planes based on the sacral base (SB) and true acetabular axis in 3D computed tomography (CT) pelvic reconstruction.
Radiological examinations of 30 physiologic pelves (60 acetabula) were included in the study. Reliability and accuracy of the method were verified by comparing acetabular angles in 2D pelvic scans with 3D reconstructions. We also applied the method to two pathologic acetabula.
Comparison of axis position in the horizontal plane revealed significant positive correlations between 2D angle measurements (acetabular anteversion angle [AAA] and anterior acetabular index [AAI]) and 3D measurement of anteversion angle (p < 0.001 and p = 0.012, respectively). In the frontal plane, there was no difference between abduction angle, measured on topogram, and inclination angle, obtained from a 3D model (p = 0.517). In the sagittal plane, there was a significant negative correlation between AAA and acetabular tilt (p < 0.001). Inter- and intra-observer reproducibility was excellent for determination of the sacral-base plane and assessment of volume, with Fleiss κ coefficients of 0.850 and 0.783, respectively, and intraclass correlation coefficients of 0.900 and 0.950, respectively. Inter-observer reproducibility for evaluation of acetabular axis ranged from 0.783 to 0.883, and intra-rater reliability ranged from 0.850 to 0.900 for all 3D angles.
Our method is a new, reliable diagnostic tool for assessing the acetabula in both normal and pathologic hip joints. The sacral-base plane can be used as a stable reference that takes the relationship of the acetabulum to the spinopelvic unit into consideration.
Additional file 1: The method described in this paper was used to determine volume and axis orientation in two patients. Computer models of the pelvis were created based on preoperative evaluative CT scans in Case 1, a 13-year-old boy with cerebral palsy and left hip joint dislocation (Figure S1a), and Case 2, a 13-year-old girl with cerebral palsy and right hip joint dislocation (Figure S2a). The results are summarized in Table S1 and depicted Figures S1b and S2b. Comparison of measurements of normal and pathologic acetabula in these patients shows large differences in acetabular orientation in the spastic hip. The acetabular axis determined using our method has a completely reversed orientation under dysplastic conditions (retroversion, posterior tilt, inclination over 90 degrees), which may influence decisions regarding surgical redirection of the acetabulum. These cases demonstrate the applicability of our method in clinical treatment. There are also differences between both dysplastic acetabula with regard to volume, a result that does not support the common view of a shallow, small-volume dysplastic acetabulum. It should be noted, however, that these are only two cases and that further investigation is warranted. Figure S1. Standard X-ray and CT reconstruction in case 1, a 13-year-old boy with cerebral palsy and left hip joint dislocation: (a) Pelvic anteroposterior X-ray; (b) pelvic 3D CT reconstruction showing the position of the acetabular axis. 3D, three-dimensional; CT, computed tomography. Figure S2. Standard X-ray and CT reconstruction in case 2, a 13-year-old girl with cerebral palsy and right hip joint dislocation: (a) Pelvic anteroposterior X-ray; (b) 3D CT reconstruction showing the position of the acetabular axis. 3D, three-dimensional; CT, computed tomography. Table S1. Surface, volume, and spatial orientation of the acetabulum.12891_2015_503_MOESM1_ESM.docx
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- An accurate method of radiological assessment of acetabular volume and orientation in computed tomography spatial reconstruction
Brian Po-Jung Chen
- BioMed Central
Neu im Fachgebiet Orthopädie und Unfallchirurgie
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