title: Measurement of femoral head penetration in polyethylene using a 3-dimensional CT-scan technique.
abstract: BACKGROUND
  Current techniques for measuring in vivo polyethylene wear suffer from a range of problems, resulting in an unacceptable lack of repeatability and/or insufficient accuracy when they are used to measure the low wear rates associated with new, highly crosslinked polyethylene. We describe an improved CT method for measurement of 3D femoral head penetration in PE acetabular cups that has sufficient accuracy and repeatability to allow assessment of the wear potential of modern implants.
  
  
  METHODS
  The accuracy and repeatability of the CT-scan method was determined by blindly repeating measurements on a precisely calibrated 28-mm prosthetic head and by comparing them with direct metrological measurements on 10 acetabular specimens with in vitro wear from machining, and on 8 explanted acetabular specimens with in vivo wear.
  
  
  RESULTS
  The intra- and interobserver errors in femoral head diameter were 0.036 mm (SD 0.044) and 0.050 mm (SD 0.022), respectively. CT estimated femoral head penetration in both all-poly and metal-backed acetabular components with accuracy ranging from 0.009 to 0.245 mm (mean 0.080; SD 0.067).
  
  
  CONCLUSIONS
  We found that the CT method is rapid, is accurate, and has repeatability and ease of availability. Using a slice thickness of 0.0625 mm, this method can detect wear—and also the threshold for the wear rate that causes osteolysis—much earlier than previous methods.
authors.affiliation: Department of Orthopaedic Surgery, Université Paris Descartes, Paris, France.
authors.forename: Eric
authors.initials: E
authors.lastname: Vandenbussche
authors.forename: Mohammed
authors.initials: M
authors.lastname: Saffarini
authors.forename: Ulrich
authors.initials: U
authors.lastname: Hansen
authors.forename: Fabienne
authors.initials: F
authors.lastname: Taillieu
authors.forename: Céline
authors.initials: C
authors.lastname: Mutschler
authors.forename: Bernard
authors.initials: B
authors.lastname: Augereau
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Gregory
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects*; D019544:Equipment Failure Analysis / Q000379:methods*; D005270:Femur Head / Q000000981:diagnostic imaging*; D006622:Hip Prosthesis / Q000009:adverse effects; D006801:Humans; D021621:Imaging, Three-Dimensional; D015588:Observer Variation; D010014:Osteolysis / Q000000981:diagnostic imaging; D020959:Polyethylene; D011474:Prosthesis Design; D011475:Prosthesis Failure; D015203:Reproducibility of Results; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D020959:Polyethylene