title: A more reliable method to assess acetabular component position.
abstract: BACKGROUND
  Acetabular component position is associated with joint function and bearing wear. Current techniques for determining acetabular component version on standard radiographs lack reliability. Other, more consistent techniques are time-consuming and require additional equipment or software.
  
  
  OBJECTIVE
  We compared three methods of acetabular component position assessment: (1) Einzel-Bild-Roentgen-Analyse (EBRA), (2) Woo and Morrey, and (3) the new ischiolateral method.
  
  
  METHODS
  We assessed axial component position for 52 hips, with at least three radiographic series, using EBRA, and on true lateral radiographs using the Woo and Morrey method and a new method that uses the ischium as a skeletal landmark, the ischiolateral method.
  
  
  RESULTS
  The mean SDs of the ischiolateral (2.15°) and EBRA (2.06°) methods were lower than that of the Woo and Morrey method (3.65°) but were not different from one another. We observed a SD of greater than 4° in 19 (36.5%) hip series using the Woo and Morrey method, compared to six series (11.5%) for both the ischiolateral and EBRA methods. Twenty-four (12.6%) Woo and Morrey measurements were greater than 4° from the mean for the hip series, compared to seven (3.8%) for ischiolateral and nine (4.7%) for EBRA. The intraclass correlation coefficients for intra- and interobserver reliability for the ischiolateral method and EBRA were the same (0.9).
  
  
  CONCLUSIONS
  Referencing the ischium standardizes pelvic position on each lateral radiograph and provides a simple and reliable means to assess axial component position, which is a surrogate for the planar anteversion measured by EBRA.
authors.affiliation: Department of Orthopaedic Surgery, Harbor-UCLA Medical Center, 1000 West Carson Street, Box 422, Torrance, CA 90509, USA. jvtiberi@gmail.com
authors.forename: John V
authors.initials: JV
authors.lastname: Tiberi
authors.forename: Nicholas
authors.initials: N
authors.lastname: Pulos
authors.forename: Michael
authors.initials: M
authors.lastname: Kertzner
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Schmalzried
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Schmlazried
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging* / Q000601:surgery*; D059925:Anatomic Landmarks; D019644:Arthroplasty, Replacement, Hip / Q000295:instrumentation*; D005260:Female; D006621:Hip Joint / Q000000981:diagnostic imaging* / Q000601:surgery*; D006622:Hip Prosthesis; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000592:standards; D007512:Ischium / Q000000981:diagnostic imaging; D016014:Linear Models; D015141:Los Angeles; D008297:Male; D015588:Observer Variation; D011237:Predictive Value of Tests; D011474:Prosthesis Design; D012015:Reference Standards; D015203:Reproducibility of Results; D012984:Software; D013997:Time Factors; D014057:Tomography, X-Ray Computed / Q000592:standards; D016896:Treatment Outcome