Wednesday, December 31, 2014

Propionibacterium and failed shoulder arthroplasty - let's use a common starting point in our quest for better understanding

Preoperative and intraoperative infection workup in apparently aseptic revision shoulder arthroplasty.

These authors present their approach to the evaluation of failed arthroplasty when there is no clinically obvious evidence of infection.

While they state that "serum inflammatory markers are essential" and that "preoperative shoulder joint aspiration culture is an important step", they also point out that these tests are more often than not normal in the face of the most common organisms cultured from failed arthroplasties: Propionibacterium and Coagulase Negative Staph. In addition frozen sections and Gram stains are insensitive to presence of these organisms.

The terminology "unexpected positive intraoperative cultures has been used, but current evidence suggests that surgeons can expect that up to 50% of revision arthroplasties will be culture positive for Propionibacterium and Coagulase Negative Staph.

This article points to the inapplicability of the definition of infection proposed by the Musculoskeletal Infection Society to the situation of revision shoulder arthroplasty. In addition, classification systems that depend on the number of cultures positive without considering the number and source of cultures taken, how long the cultures are observed, and the media on which the specimens are cultured have obvious shortcomings. 

Comment: At this point in our quest to better understand the role of Propionibacterium and Coagulase Negative Staph in the failure of shoulder arthroplasty, we need to standardize our approach to capturing the epidemiology of these organisms in revision arthroplasty by routinely obtaining five specimens of tissue or explants, culturing these specimens on aerobic and anaerobic media, and observing these cultures for 17 days. If this protocol can be applied to a large number of arthroplasty revisions, we will be able to determine the outcome of different treatment algorithms in the management of failed arthroplasty. With these data as a common starting point, we can gain some clarity on the roles of single stage and two-stage prosthesis exchange, prolonged antibiotic administration, and other strategies in the management of failed shoulder arthroplasty.


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