title: Prognostic factors for bacterial cultures positive for Propionibacterium acnes and other organisms in a large series of revision shoulder arthroplasties performed for stiffness, pain, or loosening.
abstract: BACKGROUND
  Propionibacterium acnes has been grown on culture in half of the reported cases of chronic infection associated with shoulder arthroplasty. The presence of this organism can be overlooked because its subtle presentation may not suggest the need for culture or because, in contrast to many orthopaedic infections, multiple tissue samples and weeks of culture incubation are often necessary to recover this organism. Surgical decisions regarding implant revision and antibiotic therapy must be made before the results of intraoperative cultures are known. In the present study, we sought clinically relevant prognostic evidence that could help to guide treatment decisions.
  
  
  METHODS
  We statistically correlated preoperative and intraoperative observations on 193 shoulder arthroplasty revisions that were performed because of pain, loosening, or stiffness with the results of a Propionibacterium acnes-specific culture protocol. Regression models were used to identify factors predictive of a positive culture for Propionibacterium acnes.
  
  
  RESULTS
  One hundred and eight of the 193 revision arthroplasties were associated with positive cultures; 70% of the positive cultures demonstrated growth of Propionibacterium acnes. The rate of positive cultures per shoulder increased with the number of culture specimens obtained from each shoulder. Fifty-five percent of the positive cultures required observation for more than one week. Male sex, humeral osteolysis, and cloudy fluid were each associated with significant increases of ≥ 600% in the likelihood of obtaining a positive Propionibacterium acnes culture. Humeral loosening, glenoid wear, and membrane formation were associated with significant increases of >300% in the likelihood of obtaining a positive Propionibacterium acnes culture.
  
  
  CONCLUSIONS
  Preoperative and intraoperative factors can be used to help to predict the risk of a positive culture for Propionibacterium acnes. This evidence is clinically relevant to decisions regarding prosthesis removal or retention and the need for immediate antibiotic therapy at the time of revision shoulder arthroplasty before the culture results become available.
  
  
  METHODS
  Prognostic Level II. See Instructions for Authors for a complete description of levels of evidence.
authors.affiliation: Department of Medicine, University of Washington Medical Center, Box 356420, 1959 NE Pacific Street, Seattle, WA 98195, USA.
authors.forename: Paul
authors.initials: P
authors.lastname: Pottinger
authors.forename: Susan
authors.initials: S
authors.lastname: Butler-Wu
authors.forename: Moni Blazej
authors.initials: MB
authors.lastname: Neradilek
authors.forename: Andrew
authors.initials: A
authors.lastname: Merritt
authors.forename: Alexander
authors.initials: A
authors.lastname: Bertelsen
authors.forename: Jocelyn L
authors.initials: JL
authors.lastname: Jette
authors.forename: Winston J
authors.initials: WJ
authors.lastname: Warme
authors.forename: Frederick A
authors.initials: FA
authors.lastname: Matsen
mesh_terms: D000900:Anti-Bacterial Agents / Q000627:therapeutic use; D019643:Arthroplasty, Replacement / Q000009:adverse effects* / Q000379:methods; D015331:Cohort Studies; D016001:Confidence Intervals; D005260:Female; D005500:Follow-Up Studies; D016908:Gram-Positive Bacterial Infections / Q000175:diagnosis* / Q000628:therapy; D006801:Humans; D007595:Joint Prosthesis; D016015:Logistic Models; D008297:Male; D015999:Multivariate Analysis; D016017:Odds Ratio; D011300:Preoperative Care / Q000379:methods; D011425:Propionibacterium acnes / Q000302:isolation & purification*; D011475:Prosthesis Failure; D016459:Prosthesis-Related Infections / Q000382:microbiology* / Q000601:surgery*; D011859:Radiography; D012086:Reoperation / Q000379:methods; D012189:Retrospective Studies; D018570:Risk Assessment; D012785:Shoulder Joint / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D016896:Treatment Outcome
chemical_list: D000900:Anti-Bacterial Agents