These authors performed a systematic review of the literature between 1950 and 2013 for all studies on patients having revision shoulder arthroplasty with 'unexpected positive cultures' - which they defined as positive cultures without overt signs of infection in revision shoulder arthroplasty.
They included six studies reporting a total of 1402 patients who underwent a total of 1405 revision surgeries. 235 of these shoulders had positive cultures - 149 were culture positive for Propionibacterium.
They use the term 'true' infection without defining it. Apparently they use this term to refer to cases that had recurrence of infection after the revision; 24 shoulders fell into this category.
75 shoulders received IV or oral antibiotic therapy in addition to routine postoperative dosing after the cultures became positive. These shoulders had the same rate of clinically apparent infection after the revision as those that did not receive additional postoperative antibiotics.
Comment: It is time to stop using the term 'unexpected' positive cultures in cases of revision shoulder arthroplasties. In a recent study, 103 of 193 revision arthroplasties were culture positive if appropriate culture methods were used. It is also time to stop using the term 'true' infection in that it implies that arthroplasties full of organisms such as propionibacterium will be easily recognized as being infected. To see that this is not the case, visit this recent post. Specimens harvested at the time of revision arthroplasty may be strongly culture positive years after the index procedure as shown here.
If one reviews the methods of the six studies in this review, one will see that the culture methods, intraoperative treatment, postoperative treatment and post-revision followup vary widely, confounding any firm conclusion except that many revision arthroplasties performed for loosening, pain or stiffness can be 'expected' to be culture positive for Propionibacterium.
The understanding of the role of Propionibacterium in shoulder arthroplasty failure and the means by which positive cultures should be managed will be informed by careful clinical studies that include standardized approaches for specimen harvest and culture and close clinical followup after different treatment protocols.
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