title: Standing radiographs underestimate joint width: comparison before and after resection of the joint in 34 total knee arthroplasties.
abstract: BACKGROUND
  Measurement or estimation of joint width is routinely used in the preoperative evaluation of gonarthrosis. To our knowledge, the validity and reproducibility of this procedure has not been adequately studied.
  
  
  METHODS
  We measured joint width in 34 knees (medial arthrosis: n = 22, lateral arthrosis: n = 12) on preoperative weight-bearing radiographs and on radiographs of the corresponding part of the joint after knee arthroplasty. The bone/cartilage pieces were placed in anatomical positions and loaded in a jig made of perspex. High-density film was used to obtain maximum resolution.
  
  
  RESULTS
  In medial and lateral arthrosis, the minimum joint widths were median 0.3 and 0.2 mm smaller on the radiographs of the specimens (p = 0.05, 0.04). In lateral arthrosis the differences were more scattered (95% CI: lateral: 0.1 to -1.2 mm; medial: 0 to -0.5 mm), suggesting less precise determination.
  
  
  CONCLUSIONS
  In medial arthrosis, the degree of underestimation is usually small and acceptable. More pronounced discrepancies could be found in lateral arthrosis, calling for the use of further diagnostic measures.
authors.affiliation: Department of Orthopedics, Halmstad Central Hospital, SE-301 85 Halmstad, Sweden. weidow@telia.com
authors.forename: Jonas
authors.initials: J
authors.lastname: Weidow
authors.forename: Ingvar
authors.initials: I
authors.lastname: Mars
authors.forename: Claes-Göran
authors.initials: CG
authors.lastname: Cederlund
authors.forename: Johan
authors.initials: J
authors.lastname: Kärrholm
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D011859:Radiography; D015203:Reproducibility of Results