title: Effect of screw fixation on acetabular component alignment change in total hip arthroplasty.
abstract: OBJECTIVE
  The use of screws can enhance immediate cup fixation, but the influence of screw insertion on cup position has not previously been measured. The purpose of this study was to quantitatively evaluate the effect of intra-operative screw fixation on acetabular component alignment that has been inserted with the use of a navigation system.
  
  
  METHODS
  We used a navigation system to measure cup alignment at the time of press-fit and after screw fixation in 144 hips undergoing total hip arthroplasty. We also compared those findings with factors measured from postoperative radiographs.
  
  
  RESULTS
  The mean intra-operative change of cup position was 1.78° for inclination and 1.81° for anteversion. The intra-operative change of anteversion correlated with the number of screws. The intra-operative change of inclination also correlated with medial hip centre.
  
  
  CONCLUSIONS
  The insertion of screws can induce changes in cup alignment, especially when multiple screws are used or if a more medial hip centre is required for rigid acetabular fixation.
authors.affiliation: Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-Cho Chuo-Ku, Kobe, Hyogo, 650-0017, Japan, taka2446@yg8.so-net.ne.jp.
authors.forename: Takaaki
authors.initials: T
authors.lastname: Fujishiro
authors.forename: Shinya
authors.initials: S
authors.lastname: Hayashi
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Kanzaki
authors.forename: Shingo
authors.initials: S
authors.lastname: Hashimoto
authors.forename: Nao
authors.initials: N
authors.lastname: Shibanuma
authors.forename: Masahiro
authors.initials: M
authors.lastname: Kurosaka
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging / Q000601:surgery*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000379:methods*; D017760:Bone Malalignment / Q000000981:diagnostic imaging* / Q000209:etiology; D001863:Bone Screws; D005260:Female; D006622:Hip Prosthesis; D006801:Humans; D008297:Male; D008875:Middle Aged; D011859:Radiography; D013238:Stereotaxic Techniques