title: The reliability of the anterior pelvic plane for computer navigated acetabular component placement during total hip arthroplasty: prospective study with the EOS imaging system.
abstract: BACKGROUND
  Computer navigated total hip arthroplasty is mostly based on the use of the anterior pelvic plane (APP) as a reference. EOS is a new imaging system that provides three-dimensional analysis of the pelvis in a functional position with a low dose of radiation. The aim of this study was to evaluate the reliability of the APP for placement of the cup during computer navigated THA using EOS.
  
  
  OBJECTIVE
  The reliability of the APP is limited for the placement of the acetabular cup during computer navigated THA.
  
  
  METHODS
  This was a prospective monocentric study using the EOS imaging system evaluating 44 patients in the standing position three months after computer navigated THA (Orthopilot). Reproducibility of EOS measurements were analyzed using SterEOS software and the reliability of the navigation data for the position of the cup were assessed.
  
  
  RESULTS
  Intra and interobserver reproducibility of the measurements of the orientation of the cup by EOS were good with correlation coefficients above 93% and 95% and confidence intervals of less than ±5°. Mean cup inclination and anteversion were 41.3° and 20.9° and 44.3° and 29.5° respectively in operatively and post-operatively. The differences between measurements of operative cup inclination using computer assisted navigation and the post-operative EOS measurements were significant (P<0.05) with a correlation coefficient of less than 40%.
  
  
  CONCLUSIONS
  Our study confirms the lack of precision of the APP as a reference for positioning of the acetabular component, especially in relation to anteversion. Although for many years the APP was considered to be a global reference, in fact, it is subject to significant inter-individual variations and variations during changes in position. These factors, associated with the difficulty of determining the preoperative APP, explain the lack of reliability of this reference. Preoperative evaluation of the orientation of APP by EOS and its integration into the navigation system could help the operator position these components.
  
  
  METHODS
  Level III Prospective diagnostic case controlled study.
authors.affiliation: Service de chirurgie orthopédique, hôpital central, 29, avenue de Lattre-de-Tassigny, 54000 Nancy, France; Laboratoire de biomécanique, école nationale supérieure des arts et métiers Paris tech, boulevard de l'Hôpital, 75013 Paris, France; Service de chirurgie orthopédique, hôpital d'instruction des Armées-Bégin, 69, avenue de Paris, 94160 Saint-Mandé, France. Electronic address: olive.barbier@gmail.com.
authors.forename: O
authors.initials: O
authors.lastname: Barbier
authors.affiliation: Laboratoire de biomécanique, école nationale supérieure des arts et métiers Paris tech, boulevard de l'Hôpital, 75013 Paris, France.
authors.forename: W
authors.initials: W
authors.lastname: Skalli
authors.affiliation: Service de radiologie, hôpital Brabois, rue du Morvan, 54511 Vandœuvre-lès-Nancy, France.
authors.forename: L
authors.initials: L
authors.lastname: Mainard
authors.affiliation: Service de chirurgie orthopédique, hôpital central, 29, avenue de Lattre-de-Tassigny, 54000 Nancy, France.
authors.forename: D
authors.initials: D
authors.lastname: Mainard
mesh_terms: D000077:Acetabulum / Q000601:surgery*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000379:methods*; D005260:Female; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000601:surgery*; D006622:Hip Prosthesis; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D056888:Patient Positioning; D011446:Prospective Studies; D019919:Prosthesis Implantation / Q000379:methods*; D011859:Radiography; D015203:Reproducibility of Results; D025321:Surgery, Computer-Assisted / Q000379:methods*
keywords: Anterior pelvic plane; EOS; Navigation; Total hip arthroplasty