The authors report that of 187 revision arthroplasties in their center, 48 (26%) had at least one positive culture and 17 had no other clinical signs of infection. This is a Level IV case series of these 17 patients who had unexpectedly positive results of cultures obtained at the time of their revision shoulder arthroplasty. Ten of these cultures grew out P. Acnes and 6 grew out coagulase negative staph. Laboratory studies (WBC, sedimentation rate, and C-reactive protein) were normal before surgery for these patients. The treatment of these shoulders was a single stage revision without prolonged antibiotic treatment. Only one of these patients experienced a documented recurrence of infection (had redness and swelling 6 weeks after the revision and cultured coagulase negative staph).
It is well known that P Acnes is a common culture result at the time of revision shoulder arthroplasty, even without clinical or laboratory manifestations, and that the rate of positive cultures is related to the number of cultures obtained and how long these cultures are held.
The authors conclude that "intensive antibiotic treatment strategies may not be necessary to reduce recurrent infections". While this may be the case, the data do not allow this conclusion because even though the followup was 3 years, there is no way of knowing if P Acnes or coag negative staph persisted in these shoulders. In other words, in the complex scenario of revision arthroplasty where complications are frequent (5/17) and many factors affect the outcome, clinical followup is insufficient to conclude that the shoulder is bacteria free.
It is possible, however, that the most important step in managing a shoulder prosthesis colonized with P Acnes may be removal of the component along with its biofilm and, after thorough cleaning of the surgical field, implanting a clean prosthesis under the cover of perioperative antibiotics.
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