title: Restoration of the hip center during THA performed for protrusio acetabuli is associated with better implant survival.
abstract: BACKGROUND
  Acetabular protrusio is an uncommon finding in hip arthritis. Several reconstructive approaches have been used; however the best approach remains undefined.
  
  
  OBJECTIVE
  Our purposes in this study were to (1) describe the THA survivorship for protrusio as a function of the acetabular component, (2) evaluate survivorship of the cup as a function of restoration of radiographic hip mechanics and offset, and (3) report the long-term clinical results.
  
  
  METHODS
  One hundred twenty-seven patients (162 hips) undergoing primary THA with acetabular protrusio were retrospectively reviewed. The mean age of the patients at surgery was 66±13 years, and the mean followup was 10±6 years (range, 2-25 years).The cup fixation was uncemented in 107 (83 with bone graft) and cemented in 55 hips (14 with bone graft). Preoperative and postoperative radiographs were reviewed for restoration of hip mechanics and offset.
  
  
  RESULTS
  The THA survival from aseptic cup revision at 15 years was 89% (95% CI, 75%-96%) for uncemented compared with 85% (95% CI, 68%-94%) for cemented cups. The risk of aseptic cup revision significantly increased by 24% (hazards ratio, 1.24; 95% CI, 1.02-1.5) for every 1 mm medial or lateral distance away from the native hip center of rotation to the prosthetic head center. Harris hip scores were improved by mean of 27±20 points (n=123) with a higher postoperative score for uncemented bone grafted compared with solely cemented cups (81±16 versus 71±20 points).
  
  
  CONCLUSIONS
  Restoring hip center of rotation using an uncemented cup with or without bone graft was associated with increased durability in our series. There was a 24% increase in the risk of aseptic cup revision for every 1 mm medial or lateral distance away from the native hip center to the prosthetic head center.
  
  
  METHODS
  Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
authors.affiliation: Department of Orthopedic Surgery, Mayo Clinic, 200 1st Street SW, Rochester, MN, 55905, USA.
authors.forename: Yaser M K
authors.initials: YM
authors.lastname: Baghdadi
authors.forename: A Noelle
authors.initials: AN
authors.lastname: Larson
authors.forename: Rafael J
authors.initials: RJ
authors.lastname: Sierra
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging / Q000601:surgery*; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000379:methods*; D016025:Bone Transplantation; D005260:Female; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000601:surgery*; D006622:Hip Prosthesis; D006801:Humans; D008297:Male; D008875:Middle Aged; D011474:Prosthesis Design; D011475:Prosthesis Failure; D011859:Radiography; D012189:Retrospective Studies; D012399:Rotation; D016896:Treatment Outcome