title: Low rate of Propionibacterium acnes in arthritic shoulders undergoing primary total shoulder replacement surgery using a strict specimen collection technique.
abstract: BACKGROUND
  Propionibacterium acnes is a recognized pathogen in postoperative shoulder infections. A recent study reported growth of P acnes in 42% of glenohumeral joints in primary shoulder arthroplasty, concluding that P acnes may cause shoulder osteoarthritis. Whether these results reflect true bacterial infection or specimen contamination is unclear. Our prospective study aimed to determine the rate of P acnes infection in arthritic shoulders using a strict specimen collection technique.
  
  
  METHODS
  We used modified Oxford protocol to collect tissue specimens from the glenohumeral joint of 32 consecutive patients undergoing primary shoulder arthroplasty. Specimens were cultured specifically for P acnes. Diagnosis of P acnes infection required 2 or more positive cultures and histopathology compatible with infection.
  
  
  RESULTS
  Three of 32 patients had a positive culture for P acnes. Overall, 3.125% of specimens grew P acnes without histologic evidence of infection. There were no patients with P acnes infection. The difference in culture rates between patients with idiopathic osteoarthritis and those with a predisposing cause for osteoarthritis was not significant.
  
  
  CONCLUSIONS
  We found a low rate of positive cultures for P acnes, but no P acnes infection and no difference between types of osteoarthritis. These results do not support a cause-and-effect relationship between P acnes and osteoarthritis. The differing results from previous studies are likely explained by our strict specimen collection technique, reflecting different rates of contamination rather than infection. That P acnes contamination occurs in primary shoulder arthroplasty is concerning. Further studies are needed to assess the rates of contamination in shoulder surgery, its clinical effect, and to determine optimal antibiotic prophylaxis.
authors.affiliation: Department of Orthopaedic Surgery, Royal North Shore Hospital, Sydney, NSW, Australia; Department of Orthopaedic Surgery, North Shore Private Hospital, Mater Hospital, Sydney, NSW, Australia.
authors.forename: Cristobal B
authors.initials: CB
authors.lastname: Maccioni
authors.affiliation: Department of Orthopaedic Surgery, Royal North Shore Hospital, Sydney, NSW, Australia. Electronic address: awoodbri@optusnet.com.au.
authors.forename: Adam B
authors.initials: AB
authors.lastname: Woodbridge
authors.affiliation: Department of Orthopaedic Surgery, Royal North Shore Hospital, Sydney, NSW, Australia; Department of Orthopaedic Surgery, North Shore Private Hospital, Mater Hospital, Sydney, NSW, Australia.
authors.forename: Jean-Christian Y
authors.initials: JC
authors.lastname: Balestro
authors.affiliation: Department of Infectious Diseases, Royal North Shore Hospital, Sydney, NSW, Australia.
authors.forename: Melanie C
authors.initials: MC
authors.lastname: Figtree
authors.affiliation: Department of Microbiology, Royal North Shore Hospital, Sydney, NSW, Australia.
authors.forename: Bernard J
authors.initials: BJ
authors.lastname: Hudson
authors.affiliation: Department of Orthopaedic Surgery, Royal North Shore Hospital, Sydney, NSW, Australia; Department of Orthopaedic Surgery, North Shore Private Hospital, Mater Hospital, Sydney, NSW, Australia.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Cass
authors.affiliation: Department of Orthopaedic Surgery, Royal North Shore Hospital, Sydney, NSW, Australia; Department of Orthopaedic Surgery, North Shore Private Hospital, Mater Hospital, Sydney, NSW, Australia.
authors.forename: Allan A
authors.initials: AA
authors.lastname: Young
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001168:Arthritis / Q000601:surgery; D019643:Arthroplasty, Replacement; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011425:Propionibacterium acnes / Q000302:isolation & purification*; D011446:Prospective Studies; D012785:Shoulder Joint / Q000382:microbiology* / Q000601:surgery
keywords: Propionibacterium acnes; arthroplasty; contamination; culture; infection; osteoarthritis; shoulder