title: A radiological technique for the assessment of wear in prosthetic knee replacements.
abstract: OBJECTIVE
  Wear of the polyethylene insert is a well-recognised cause of implant failure in total knee replacements. The purpose of this study was to evaluate a simple, digital fluoroscopic technique for the assessment of wear in knee prostheses.
  
  
  METHODS
  Fluoroscopic images of knee prostheses were produced both of a phantom and in a patient group. Joint space thickness was measured by reference to a known diameter. Measurements were made to assess repeatability of positioning, inter-and intra-observer variance and the effect of angulation.
  
  
  RESULTS
  Standard phantom images showed small variation between measurements, high inter-reader correlation (Pearson's correlation coefficient, r=0.98, P<0.001; coefficient of variation=0.53%) and low intra-reader variation (coefficient of variation=0.57%). Inter- and intra-imager variation were low (coefficient of variation=1.05% and 0.88%, respectively). In the patient group, the range of joint space measurements was 1.9-8.9 mm. The coefficient of variation in insert measurements on repeated images was 2.0%. Repeatability of measurements was 0.2 mm with 99% confidence interval.
  
  
  CONCLUSIONS
  This technique allows repeatable, precise measurement of insert thickness. The technique may be adapted to any implant where a reliable calibrating distance is present.
authors: Department of Radiology, North Tees and Hartlepool NHS Trust, c/o Hartlepool General Hospital, Cleveland, UK.
authors: I G
authors: IG
authors: Hide
authors: A J
authors: AJ
authors: Grainger
authors: I W
authors: IW
authors: Wallace
authors: A
authors: A
authors: Hui
authors: R S
authors: RS
authors: Campbell
mesh_terms: D005471:Fluoroscopy / Q000379:methods; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging; D007720:Knee Prosthesis; D019047:Phantoms, Imaging; D011475:Prosthesis Failure; D015203:Reproducibility of Results