title: Cup positioning in total hip arthoplasty: spatial alignment of the acetabular entry plane.
abstract: OBJECTIVE
  Correct cup positioning is one of the keys for successful total hip replacement. There are mechanical and computer assistant guides for correct cup positioning in the market. To optimize the cup positioning, the use of navigation systems is recommended. The aim of this study was to compare spatial orientation of the acetabulary entry plane in relation to tables plane which is used by mechanical guides as well as anterior pelvic plane used for cup orientation by navigation systems.
  
  
  METHODS
  CT raw data of 80 Caucasians (160 acetabuli) (done in supine position) with osteoartritic hips were collected. 3-D pelvic reconstruction was generated using Amira software (Visage Imaging Berlin, Germany). Anterior pelvic plane and acetabulary entry plane were defined by reliable anatomical landmarks. Spatial orientation were calculated by a custom made program code for the Amira software.
  
  
  RESULTS
  There were no differences between anterior pelvic plane and table's plane as well as spatial orientation of acetabulary entry plane of both acetabuli in relation to anterior pelvic plane or table's plane. Furthermore, there was no correlation between age, sex or body mass index and spatial orientation of the acetabulary entry plane as well.
  
  
  CONCLUSIONS
  The use of mechanical alignment guides for cup orientation during total hip arthroplasty based on table's plane in patient's supine position is a successful method to achieve proper cup orientation.
authors.affiliation: Department of Orthopedic Surgery, Martin Luther University Halle-Wittenberg, Magdeburger Strasse 22, 06112 Halle (Saale), Germany. david.wohlrab@medizin.uni-halle.de
authors.forename: David
authors.initials: D
authors.lastname: Wohlrab
authors.forename: Florian
authors.initials: F
authors.lastname: Radetzki
authors.forename: Hansrudi
authors.initials: H
authors.lastname: Noser
authors.forename: Thomas
authors.initials: T
authors.lastname: Mendel
mesh_terms: D000077:Acetabulum / Q000033:anatomy & histology; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000295:instrumentation / Q000379:methods*; D005260:Female; D006622:Hip Prosthesis; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D008953:Models, Anatomic; D058638:Operating Tables; D015207:Osteoarthritis, Hip / Q000000981:diagnostic imaging / Q000601:surgery; D012189:Retrospective Studies; D016683:Supine Position; D025321:Surgery, Computer-Assisted / Q000295:instrumentation / Q000379:methods*; D014057:Tomography, X-Ray Computed; D055815:Young Adult