title: Aseptic loosening of cobalt chromium monoblock sockets after hip resurfacing.
abstract: BACKGROUND
  Acetabular component loosening is a leading cause for revision after metal-on-metal hip resurfacing arthroplasty (MMHRA). We aimed to identify potential risk factors and determine radiographic signs associated with this mode of failure.
  
  
  METHODS
  From a series of 1375 hips treated with MMHRA, 21 (20 patients) underwent revision surgery secondary to aseptic loosening of the acetabular component and 6 patients had a radiographically loose acetabular component. A control group of 27 hips (26 patients) was selected among the patients that did not have a revision, and was matched for age, gender, component size and diagnosis.
  
  
  RESULTS
  Mean time to revision in the loosening group was 103.0 months and the mean time of follow-up in the control group was 161.4 months. We found greater activity levels, range of motion scores, and cup abduction angles in the loosening group. The centre-edge (CE) angle of Wiberg was 10° lower in the loosening group compared with the control group. In addition, 11 of the hips from the study group presented a sclerotic halo superior to the cup on the last radiograph vs. none in the control group. There was no difference in the prevalence of postoperative reaming gaps or radiographic signs of neck-cup impingement between the 2 groups.
  
  
  CONCLUSIONS
  Risk factors for acetabular loosening included hip dysplasia with low CE angle, and a large cup abduction angle. The patient's level of activity influences the appearance of symptoms and the time to revision. We recommend selecting patients with a sufficient CE angle and properly orienting the cup.
authors.affiliation: Joint Replacement Institute at St Vincent Medical Center, Los Angeles, California - USA.
authors.forename: Harlan C
authors.initials: HC
authors.lastname: Amstutz
authors.affiliation: Joint Replacement Institute at St Vincent Medical Center, Los Angeles, California - USA.
authors.forename: Michel J
authors.initials: MJ
authors.lastname: Le Duff
mesh_terms: D000077:Acetabulum / Q000601:surgery; D000293:Adolescent; D000328:Adult; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects* / Q000379:methods; D016022:Case-Control Studies; D002857:Chromium / Q000737:chemistry; D003035:Cobalt / Q000737:chemistry; D005260:Female; D006622:Hip Prosthesis; D006801:Humans; D008297:Male; D008875:Middle Aged; D010147:Pain Measurement; D011379:Prognosis; D011474:Prosthesis Design; D011475:Prosthesis Failure; D016059:Range of Motion, Articular / Q000502:physiology*; D020127:Recovery of Function; D012086:Reoperation / Q000379:methods; D012189:Retrospective Studies; D018570:Risk Assessment; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: D002857:Chromium; D003035:Cobalt