These authors obtained deep cultures for Cutibacterium in 134 patients having primary anatomic or reverse total shoulder arthroplasty.One hundred and thirty-four patients were included. The average age of the cohort was 67.6 +/- 13.9 (range 41 to 91) years, with 82 (62.1%) men.
In each case, five tissue samples were collected and processed in a single laboratory for culture on aerobic and anaerobic media for 13 days.
Minimum 2-year functional outcomes scores (ASES and SANE) and reoperation data was analyzed.
Forty-two (31.3%) patients had positive cultures: Thirty patients (22.4%) had positive cultures with C. acnes. Staphylococcus epidermidis (n = 7) was the second most commonly cultured organism
There was no statistically significant difference in postoperative functional outcome scores (ASES: 82.5 vs 81.9; p=0.89, SANE: 79.5 vs 82.1; p=0.54) between culture positive and culture negative cohorts. No cases of infection were identified.
Two patients (4.8%; 2/42) with positive cultures required reoperation compared to four patients (5.6%; 4/71) without positive cultures.
Comment: Cutibacterium is the most common cause of periprosthetic shoulder infections. It is the organism most commonly recovered in failed shoulder arthroplasties.
Cutibacterium exists in the pilosebaceous units of normal skin, especially in young healthy males (see this link). It cannot be eliminated by usual surgical prophylaxis (showers, skin preparation). Thus when shoulder arthroplasties are performed in these patients, the skin incision allows Cutibacterium to enter the surgical field. Whether this inoculation results in an infection depends on a number of factors, including the number of bacteria introduced into the wound, the virulence of the bacteria, the strength of the host defenses against Cutibacterium and the steps taken by the surgeon to manage the inoculum (IV antibiotics, wound irrigation, topical antibiotics).
In this study, positive deep cultures at the time of arthroplasty were not followed by recognized periprosthetic infections at two years. These findings suggest that the patient and the surgeon may have effectively managed the bacteria introduced into the joint.
It would be of interest to know the degree of positivity of the positive cultures to get an estimate of the load of bacteria found in the arthroplasty wound (see this link).
It would be of interest to know the rate of culture positivity of sterile control samples obtained from this operating room, recalling that some centers have reported a high positive culture rate for sterile swabs or gauze sponges exposed in the OR (see this link).
This article should not be interpreted as indicating that the introduction of Cutibacterium into arthroplasty wounds is clinically unimportant, but rather that for most patients a standard surgical protocol of prophylaxis appears to minimize the risk of periprosthetic infection.
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