title: Assessing wear of the acetabular cup using computed tomography: an ex vivo study.
abstract: OBJECTIVE
  To validate a clinically useful method for measuring acetabular cup wear using computed tomography (CT).
  
  
  METHODS
  Eight uncemented acetabular cups were scanned twice ex vivo using CT. The linear penetration depth of the femoral component head into the cup and the thickness of the remaining polyethylene liner were measured in the CT volumes using dedicated software. Two independent examiners twice assessed each volume. The CT measurements were compared to direct measurements using a coordinate measuring device and micrometer measurements.
  
  
  RESULTS
  Accuracy of wear measurements expressed as penetration depth was +/-0.6 and +/- 1.0 mm for the two examiners, respectively, with no significant differences between examiners, trials, and CT scans. Accuracy of measurements of remaining polyethylene was +/- 1.3 and +/- 1.0 mm, respectively, for the two examiners. Systematic differences between examiners were found, but no significant differences between trials and CT scans. These differences were due to different interpretations of metal artifacts in the volumes.
  
  
  CONCLUSIONS
  The proposed CT method for evaluating wear as head penetration depth allows for reliable wear detection at a clinically relevant level. Measurements of remaining polyethylene on CT volumes are not as reliable as wear measurements owing to metal artifacts.
authors.affiliation: Department of Radiology, Karolinska University Hospital Solna, Stockholm, Sweden. charlotta.olivecrona@karolinska.se
authors.forename: L
authors.initials: L
authors.lastname: Olivecrona
authors.forename: A
authors.initials: A
authors.lastname: Jedenmalm
authors.forename: P
authors.initials: P
authors.lastname: Aspelin
authors.forename: L
authors.initials: L
authors.lastname: Weidenhielm
authors.forename: M E
authors.initials: ME
authors.lastname: Noz
authors.forename: G Q
authors.initials: GQ
authors.lastname: Maguire
authors.forename: M P
authors.initials: MP
authors.lastname: Zeleznik
authors.forename: H
authors.initials: H
authors.lastname: Olivecrona
mesh_terms: D020878:Device Removal; D019544:Equipment Failure Analysis / Q000379:methods*; D005240:Feasibility Studies; D006622:Hip Prosthesis; D006801:Humans; D021621:Imaging, Three-Dimensional; D020959:Polyethylene; D011475:Prosthesis Failure; D015203:Reproducibility of Results; D014057:Tomography, X-Ray Computed
chemical_list: D020959:Polyethylene