Monday, June 16, 2014

Propionibacterium infection of shoulder replacement - risk factors and our approach

Patient and Procedure-specific Risk Factors for Deep Infection After Primary Shoulder Arthroplasty.

These authors sought to identify patient-specific risk factors for deep infection, and the pathogen profile after primary shoulder arthroplasty in a series of 3906  patients with a mean followup of 2.7 years (1 day-7 years). The study endpoint was the diagnosis of deep infection, which was defined as revision surgery for infection supported clinically by more than one of the following criteria: purulent drainage from the deep incision, fever, localized pain or tenderness, a positive deep culture, and/or a diagnosis of deep infection made by the operating surgeon based on intraoperative findings.

They found that young age, male sex, reverse total shoulder, and arthroplasty for trauma were associated with an increased risk of infection. Specifically, for every 1-year increase in age, a 5%  lower risk of infection was observed. Male patients had a risk of infection of 2.59 times greater than female patients. Patients undergoing primary reverse total shoulder arthroplasty had a 6.11 times greater risk of infection compared with patients having primary unconstrained total shoulder arthroplasty. Patients having traumatic arthroplasties were 2.98 times more likely to have an infection develop than patients having elective arthroplasties.

During the study period, 45 (1.0%) patients had a diagnosis of deep infection at a median of 212 days
Of these 45 patients, 30 (67%) had infections within the first year postoperatively and the remaining patients had infections occur after 1 year.

The most common organism was Propionibacterium acnes with 14 (27.5%) cultures. There were seven
(13.7%) cultures of coagulase-negative staphylococcus infections, four (7.8%) caused by methicillin-resistant Staphylococcus aureus , and three (5.9%) caused by methicillin- sensitive S aureus . We found three (5.9%) cultures of Finegoldia magna , three (5.9%) cultures of Enterobacter , and eight (15.7%) infections with negative cultures with the diagnosis made clinically and intraoperatively. Five (11%) patients had polymicrobial infection (more than one infectious organism isolated).

Comment: This study is important because it confirms that young age and male sex and arthroplasty for trauma are major risk factors for shoulder arthroplasty infection. It is likely that the rate of positive cultures in this study would have been much higher if a standard culture protocol had been used for all revision arthroplasties, in that it is now recognized that as many as 40% of shoulder arthroplasty revisions are culture positive even though the symptoms do not suggest infection (see this post).

With these risk factors in mind, surgeons may wish to apply an upgraded antibiotic prophylaxis to patients at high risk. We are currently using Cephtriaxone and Vancomycin for 24 hours for all shoulder arthroplasties. 

For all revision arthroplasties, we obtain five specimens and submit them for Propionibacterium-specific cultures. Each patient is then placed on the "yellow" or "red" protocol based in the surgeon's suspicion of infection until the results of cultures are finalized at three weeks.

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