title: Chronological changes in functional cup position at 10 years after total hip arthroplasty.
abstract: OBJECTIVE
  This study aims to clarify the chronological changes in functional cup position at a minimum follow-up of 10 years after total hip arthroplasty (THA), and to identify the risk factors influencing a significant difference in functional cup position during the postoperative follow-up period.
  
  
  METHODS
  We evaluated the chronological changes in functional cup position at a minimum follow-up of 10 years after THA in 58 patients with unilateral hip osteoarthritis. Radiographic cup position was measured on anteroposterior pelvic radiographs with the patient in the supine position, whereas functional cup position was recorded in the standing position. Radiographs were obtained before, 3 weeks after, and every 1 year after surgery.
  
  
  RESULTS
  Functional cup anteversion (F-Ant) increased over time, and was found to have significantly increased at final follow-up compared to that at 3 weeks after surgery (p<0.01). The maximum postoperative change in F-Ant was 17.0° anteriorly; 12 cases (21%) showed a postoperative change in F-Ant by >10° anteriorly. Preoperative posterior pelvic tilt in the standing position and vertebral fractures after THA were significant predictors of increasing functional cup anteversion.
  
  
  CONCLUSIONS
  Although chronological changes in functional cup position do occur after THA, their magnitude is relatively low. However, posterior impingement is likely to occur, which may cause edge loading, wear of the polyethylene liner, and anterior dislocation of the hip. We believe that, for the combined anteversion technique, the safe zone should probably be 5°-10° narrower in patients predicted to show considerable changes in functional cup position compared with standard cases.
authors.affiliation: Department of Orthopaedic Surgery, Kochi Medical School, Nankoku - Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Okanoue
authors.affiliation: Department of Orthopaedic Surgery, Kochi Medical School, Nankoku - Japan.
authors.forename: Masahiko
authors.initials: M
authors.lastname: Ikeuchi
authors.affiliation: Department of Orthopaedic Surgery, Kochi Medical School, Nankoku - Japan.
authors.forename: Shogo
authors.initials: S
authors.lastname: Takaya
authors.affiliation: Department of Orthopaedic Surgery, Kochi Medical School, Nankoku - Japan.
authors.forename: Masashi
authors.initials: M
authors.lastname: Izumi
authors.affiliation: Department of Orthopaedic Surgery, Kochi Medical School, Nankoku - Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Aso
authors.affiliation: Department of Orthopaedic Surgery, Kochi Medical School, Nankoku - Japan.
authors.forename: Teruhiko
authors.initials: T
authors.lastname: Kawakami
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000379:methods*; D005260:Female; D005500:Follow-Up Studies; D005544:Forecasting; D006801:Humans; D008297:Male; D008875:Middle Aged; D015207:Osteoarthritis, Hip / Q000175:diagnosis / Q000503:physiopathology / Q000601:surgery*; D011184:Postoperative Period; D011187:Posture / Q000502:physiology*; D011859:Radiography