title: Intraoperative synovial C-reactive protein is as useful as frozen section to detect periprosthetic hip infection.
abstract: BACKGROUND
  Synovial quantification of C-reactive protein (SCRP) has been recently published with high sensitivity and specificity in the diagnosis of periprosthetic joint infection. However, to our knowledge, no studies have compared the use of this test with intraoperative frozen section, which is considered by many to be the best intraoperative test now available.
  
  
  OBJECTIVE
  We asked whether intraoperative SCRP could lead to comparable sensitivity, specificity, and predictive values as intraoperative frozen section in revision total hip arthroplasty.
  
  
  METHODS
  A prospective study was performed including 76 patients who underwent hip revision for any cause. SCRP quantification (using 9.5 mg/L as denoting infection) and the analysis of frozen section of intraoperative samples (five or more polymorphonuclear leukocytes under high magnification in 10 fields) were performed in all the patients. The definitive diagnosis of an infection was determined according to the Musculoskeletal Infection Society (MSIS). In this group, 30% of the patients were diagnosed with infection using the MSIS criteria (23 of 76 patients).
  
  
  RESULTS
  With the numbers available, there were no differences between SCRP and frozen section in terms of their ability to diagnose infection. The sensitivity of SCRP was 90% (95% confidence interval [CI], 70.8%-98.6%), the specificity was 94% (95% CI, 84.5%-98.7%), the positive predictive value was 87% (95% CI, 66.3%-97%), and the negative predictive value was 96% (95% CI, 87%-99.4%); the sensitivity, specificity, positive predictive value, and negative predictive value were the same using frozen sections to diagnose infection. The positive likelihood ratio was 16.36 (95% CI, 5.4-49.5), indicating a low probability of an individual without the condition having a positive test, and the negative likelihood ratio was 0.10 (95% CI, 0.03-0.36), indicating low probability of an individual without the condition having a negative test.
  
  
  CONCLUSIONS
  We found that quantitative SCRP had similar diagnostic value as intraoperative frozen section with comparable sensitivity, specificity, and predictive value in a group of patients undergoing revision total hip arthroplasty. In our institution, SCRP is easier to obtain, less expensive, and less dependent on the technique of obtaining and interpreting a frozen section. If our findings are confirmed by other groups, we suggest that quantitative SCRP be considered as a viable alternative to frozen section.
  
  
  METHODS
  Level I, diagnostic study.
authors.affiliation: Hip Surgery Unit, Institute of Orthopaedics "Carlos E. Ottolenghi", Italian Hospital of Buenos Aires, Potosí 4247, C1199ACK, Buenos Aires, Argentina. martin.buttaro@hospitalitaliano.org.ar.
authors.forename: Martin A
authors.initials: MA
authors.lastname: Buttaro
authors.affiliation: Hip Surgery Unit, Institute of Orthopaedics "Carlos E. Ottolenghi", Italian Hospital of Buenos Aires, Potosí 4247, C1199ACK, Buenos Aires, Argentina.
authors.forename: Gabriel
authors.initials: G
authors.lastname: Martorell
authors.affiliation: Hip Surgery Unit, Institute of Orthopaedics "Carlos E. Ottolenghi", Italian Hospital of Buenos Aires, Potosí 4247, C1199ACK, Buenos Aires, Argentina.
authors.forename: Mauricio
authors.initials: M
authors.lastname: Quinteros
authors.affiliation: Hip Surgery Unit, Institute of Orthopaedics "Carlos E. Ottolenghi", Italian Hospital of Buenos Aires, Potosí 4247, C1199ACK, Buenos Aires, Argentina.
authors.forename: Fernando
authors.initials: F
authors.lastname: Comba
authors.affiliation: Hip Surgery Unit, Institute of Orthopaedics "Carlos E. Ottolenghi", Italian Hospital of Buenos Aires, Potosí 4247, C1199ACK, Buenos Aires, Argentina.
authors.forename: Gerardo
authors.initials: G
authors.lastname: Zanotti
authors.affiliation: Hip Surgery Unit, Institute of Orthopaedics "Carlos E. Ottolenghi", Italian Hospital of Buenos Aires, Potosí 4247, C1199ACK, Buenos Aires, Argentina.
authors.forename: Francisco
authors.initials: F
authors.lastname: Piccaluga
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects* / Q000295:instrumentation*; D001431:Bacteriological Techniques; D015415:Biomarkers / Q000032:analysis; D002097:C-Reactive Protein / Q000032:analysis*; D005260:Female; D005629:Frozen Sections; D006621:Hip Joint / Q000382:microbiology / Q000601:surgery*; D006622:Hip Prosthesis / Q000009:adverse effects*; D006801:Humans; D016013:Likelihood Functions; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011446:Prospective Studies; D016459:Prosthesis-Related Infections / Q000175:diagnosis* / Q000382:microbiology / Q000473:pathology / Q000601:surgery; D012086:Reoperation; D012307:Risk Factors; D000074402:Synovectomy; D013583:Synovial Membrane / Q000737:chemistry* / Q000382:microbiology
chemical_list: D015415:Biomarkers; D002097:C-Reactive Protein