title: Diagnostic accuracy of intra-articular C-reactive protein assay in periprosthetic knee joint infection--a preliminary study.
abstract: BACKGROUND
  Periprosthetic joint infection often raises diagnostic challenges, as the published criteria are heterogeneous. New markers for predicting periprosthetic infection have been evaluated. Here, we assessed one of these markers, C-reactive protein (CRP), in joint fluid.
  
  
  OBJECTIVE
  We hypothesised that intra-articular CRP levels would perform better than serum CRP concentrations in diagnosing knee prosthesis infection.
  
  
  METHODS
  We prospectively included 30 patients including 10 with native-knee effusions, 11 with prosthetic-knee aseptic effusions, and 11 with prosthetic-knee infection defined using 2011 Musculoskeletal Society criteria. Serum CRP was assayed using turbidimetry or nephelometry and intra-articular CRP using nephelometry. Appropriate statistical tests were performed to compare the three groups; P values < 0.05 were considered significant.
  
  
  RESULTS
  Serum and intra-articular CRP levels were 5- to 16-fold higher in the group with periprosthetic infection than in the other two groups. Although the areas under the ROC curves were not significantly different, the likelihood ratios associated with the selected cut-offs suggested superiority of intra-articular CRP: a value > 2.78 mg/L suggested possible infection (100% sensitivity and 82% specificity) and a value > 5.37 mg/L probable infection (90% sensitivity and 91% specificity).
  
  
  CONCLUSIONS
  Our findings suggest a possible role for intra-articular CRP assay in diagnosing knee prosthesis infection and perhaps periprosthetic infection at any site.
  
  
  METHODS
  Level III, diagnostic study, development of a diagnostic criterion in consecutive patients comparatively to a reference standard.
authors.affiliation: Service de rhumatologie, Hôpitaux Universitaires de Strasbourg, avenue Molière, 67200 Strasbourg, France.
authors.forename: C
authors.initials: C
authors.lastname: Ronde-Oustau
authors.affiliation: Centre de chirurgie orthopédique et de la main, Hôpitaux Universitaires de Strasbourg, 10, avenue Baumann, 67400 Illkirch, France.
authors.forename: Y
authors.initials: Y
authors.lastname: Diesinger
authors.affiliation: Centre de chirurgie orthopédique et de la main, Hôpitaux Universitaires de Strasbourg, 10, avenue Baumann, 67400 Illkirch, France. Electronic address: jean-yves.jenny@chru-strasbourg.fr.
authors.forename: J-Y
authors.initials: JY
authors.lastname: Jenny
authors.affiliation: Centre de chirurgie orthopédique et de la main, Hôpitaux Universitaires de Strasbourg, 10, avenue Baumann, 67400 Illkirch, France.
authors.forename: M
authors.initials: M
authors.lastname: Antoni
authors.affiliation: Centre de chirurgie orthopédique et de la main, Hôpitaux Universitaires de Strasbourg, 10, avenue Baumann, 67400 Illkirch, France.
authors.forename: J
authors.initials: J
authors.lastname: Gaudias
authors.affiliation: Centre de chirurgie orthopédique et de la main, Hôpitaux Universitaires de Strasbourg, 10, avenue Baumann, 67400 Illkirch, France.
authors.forename: C
authors.initials: C
authors.lastname: Boeri
authors.affiliation: Service de rhumatologie, Hôpitaux Universitaires de Strasbourg, avenue Molière, 67200 Strasbourg, France.
authors.forename: J
authors.initials: J
authors.lastname: Sibilia
authors.affiliation: Laboratoire de biochimie et biologie moléculaire, Hôpitaux Universitaires de Strasbourg, 1, place de l'Hôpital, 67000 Strasbourg, France.
authors.forename: J-M
authors.initials: JM
authors.lastname: Lessinger
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee; D015415:Biomarkers / Q000097:blood; D002097:C-Reactive Protein / Q000032:analysis*; D005260:Female; D006801:Humans; D007720:Knee Prosthesis / Q000009:adverse effects*; D008297:Male; D011446:Prospective Studies; D016459:Prosthesis-Related Infections / Q000097:blood / Q000175:diagnosis*; D012680:Sensitivity and Specificity
chemical_list: D015415:Biomarkers; D002097:C-Reactive Protein
keywords: Intra-articular CRP; Periprosthetic infection; Surgical site infection; Total joint infection