title: An accurate method of radiological assessment of acetabular volume and orientation in computed tomography spatial reconstruction.
abstract: BACKGROUND
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Paediatric Orthopaedics and Traumatology, Poznan University of Medical Sciences, ul. Fredry 10, 61-701, Poznan, Poland. mjsl@poczta.onet.pl.
authors.forename: Marek
authors.initials: M
authors.lastname: Jóźwiak
authors.affiliation: Division of Virtual Engineering, Poznan University of Technology, ul. Piotrowo 3, 60-965, Poznan, Poland. rychlik.michal@poczta.fm.
authors.forename: Michał
authors.initials: M
authors.lastname: Rychlik
authors.affiliation: Department of Paediatric Orthopaedics and Traumatology, Poznan University of Medical Sciences, ul. Fredry 10, 61-701, Poznan, Poland. ortopediadziecieca@gmail.com.
authors.forename: Bartosz
authors.initials: B
authors.lastname: Musielak
authors.affiliation: Department of Paediatric Orthopaedics and Traumatology, Poznan University of Medical Sciences, ul. Fredry 10, 61-701, Poznan, Poland. brianchen.md@icloud.com.
authors.forename: Brian Po-Jung
authors.initials: BP
authors.lastname: Chen
authors.affiliation: Department of Paediatric Orthopaedics and Traumatology, Poznan University of Medical Sciences, ul. Fredry 10, 61-701, Poznan, Poland. maciejidzior@poczta.onet.pl.
authors.forename: Maciej
authors.initials: M
authors.lastname: Idzior
authors.affiliation: Department of Orthopaedics and Paediatric Orthopaedics, Medical University of Lodz, ul. Kościuszki 4, Łódź, Poland. andrzejgr@op.pl.
authors.forename: Andrzej
authors.initials: A
authors.lastname: Grzegorzewski
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging*; D000293:Adolescent; D005260:Female; D006617:Hip Dislocation / Q000000981:diagnostic imaging*; D006621:Hip Joint / Q000000981:diagnostic imaging*; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008297:Male; D061330:Multidetector Computed Tomography / Q000379:methods*; D015588:Observer Variation; D011237:Predictive Value of Tests; D011446:Prospective Studies; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results