title: Does hemipelvis structure and position influence acetabulum orientation?
abstract: BACKGROUND
  Although acetabulum orientation is well established anatomically and radiographically, its relation to the innominate bone has rarely been addressed. If explored, it could open the discussion on patomechanisms of such complex disorders as femoroacetabular impingement (FAI). We therefore evaluated the influence of pelvic bone position and structure on acetabular spatial orientation. We describe this relation and its clinical implications.
  
  
  METHODS
  This retrospective study was based on computed tomography scanning of three-dimensional models of 31 consecutive male pelvises (62 acetabulums). All measurements were based on CT spatial reconstruction with the use of highly specialized software (Rhinoceros). Relations between acetabular orientation (inclination, tilt, anteversion angles) and pelvic structure were evaluated. The following parameters were evaluated to assess the pelvic structure: iliac opening angle, iliac tilt angle, interspinous distance (ISD), intertuberous distance (ITD), height of the pelvis (HP), and the ISD/ITD/HP ratio. The linear and nonlinear dependence of the acetabular angles and hemipelvic measurements were examined with Pearson's product - moment correlation and Spearman's rank correlation coefficient. Correlations different from 0 with p < 0.05 were considered statistically significant.
  
  
  RESULTS
  Comparison of the axis position with pelvis structure with orientation in the horizontal plane revealed a significant positive correlation between the acetabular anteversion angle and the iliac opening angle (p = 0.041 and 0.008, respectively). In the frontal plane, there was a positive correlation between the acetabular inclination angle and the iliac tilt angle (p = 0.025 and 0.014, respectively) and the acetabular inclination angle and the ISD/ITD/HP ratio (both p = 0.048).
  
  
  CONCLUSIONS
  There is a significant correlation of the hemipelvic structure and acetabular orientation under anatomic conditions, especially in the frontal and horizontal planes. In the anteroposterior view, the more tilted-down innominate bone causes a more caudally oriented acetabulum axis, whereas in the horizontal view this relation is reversed. This study may serve as a basis for the discussion on the role of the pelvis in common disorders of the hip.
authors.affiliation: Department of Paediatric Orthopaedics and Traumatology, Poznan University of Medical Sciences, Fredry 10, Poznan, 61-701, 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, Fredry 10, Poznan, 61-701, Poland.
authors.forename: Marek
authors.initials: M
authors.lastname: Jóźwiak
authors.affiliation: Division of Virtual Engineering, Poznan University of Technology, Piotrowo 3, Poznan, 60-965, Poland.
authors.forename: Michał
authors.initials: M
authors.lastname: Rychlik
authors.affiliation: Department of Paediatric Orthopaedics and Traumatology, Poznan University of Medical Sciences, Fredry 10, Poznan, 61-701, Poland.
authors.forename: Brian Po-Jung
authors.initials: BP
authors.lastname: Chen
authors.affiliation: Department of Paediatric Orthopaedics and Traumatology, Poznan University of Medical Sciences, Fredry 10, Poznan, 61-701, Poland.
authors.forename: Maciej
authors.initials: M
authors.lastname: Idzior
authors.affiliation: Department of Orthopaedics and Paediatric Orthopaedics, Medical University of Lodz, Kościuszki 4, Łódź, Poland.
authors.forename: Andrzej
authors.initials: A
authors.lastname: Grzegorzewski
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging*; D059925:Anatomic Landmarks; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D008953:Models, Anatomic; D061330:Multidetector Computed Tomography; D010384:Pelvic Bones / Q000000981:diagnostic imaging*; D011857:Radiographic Image Interpretation, Computer-Assisted; D012189:Retrospective Studies; D012984:Software
keywords: Computed tomography; Hip joint; Pelvic bone; Sacral base plane; Spatial orientation