title: Retrieval and radiographic analysis of the Contour antiprotrusio cage.
abstract: BACKGROUND
  Acetabular reconstruction in the setting of severe bone loss or pelvic discontinuity remains a challenging problem. Multiple methods of treatment have been described including antiprotrusio cages (APCs). The objective of this study is to combine biomechanical analysis of retrieved APCs with radiographic and clinical data to determine which factors influence or predict APC failure.
  
  
  METHODS
  41 APCs were identified. Sequential radiographs were examined for cage and polyethylene cup abduction angles, change in centre of rotation, screw placement, progression of cage failure, and failure mechanism. Cages were manually examined for gross macroscopic findings, breakage, and the location of breakage. High-resolution microscopy was used for further analysis.
  
  
  RESULTS
  24 cages were included in the analysis. Mean age of patients was 64.5 years (range 43-85 years); average length of implantation was 42.5 months (range 3-108 months). Average cage abduction angles were 56°; abduction for the cemented polyethylene cup was 44°. 14 of 24 cages were broken; 10 were intact. Of the broken cages, 10/14 broke through a screw hole in the ischial flange or just superior to the ischial flange. In the intact group, 6/10 failed due to pullout of the ischial screws.
  
  
  CONCLUSIONS
  All cages had superior and lateralised centres of rotation. The majority of cages failed due to breakage or pullout at the ischial flange. Pelvic discontinuity was a large risk factor for a broken cage. Future design and technique modifications may result in superior outcomes in these complex acetabular reconstructions.
authors.affiliation:  Division of Adult Reconstruction, Department of Orthopaedic Surgery, NYU Hospital for Joint Diseases, New York - USA.
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Vigdorchik
authors.affiliation:  Division of Adult Reconstruction, Department of Orthopaedic Surgery, NYU Hospital for Joint Diseases, New York - USA.
authors.forename: Richard S
authors.initials: RS
authors.lastname: Yoon
authors.affiliation:  Division of Adult Reconstruction, Department of Orthopaedic Surgery, Hospital for Special Surgery, New York - USA.
authors.forename: Susannah L
authors.initials: SL
authors.lastname: Gilbert
authors.affiliation:  Division of Adult Reconstruction, Department of Orthopaedic Surgery, Hospital for Special Surgery, New York - USA.
authors.forename: Joseph D
authors.initials: JD
authors.lastname: Lipman
authors.affiliation:  Division of Adult Reconstruction, Department of Orthopaedic Surgery, Hospital for Special Surgery, New York - USA.
authors.forename: Mathias P
authors.initials: MP
authors.lastname: Bostrom
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging* / Q000601:surgery; D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects* / Q000379:methods; D016208:Databases, Factual; D020878:Device Removal / Q000379:methods; D005260:Female; D005500:Follow-Up Studies; D006622:Hip Prosthesis; D006801:Humans; D008297:Male; D008875:Middle Aged; D011474:Prosthesis Design / Q000379:methods*; D011475:Prosthesis Failure; D011859:Radiography / Q000379:methods; D012086:Reoperation / Q000379:methods; D012189:Retrospective Studies; D018570:Risk Assessment