These authors point out that Propionibacterium are commonly recovered in revision shoulder surgery and that they are also present in specimens from primary shoulder arthroplasty.
The exclusion criteria for this study were a previous shoulder surgical procedure, shoulder infection, previous proximal humeral fracture, use of antibiotics within 2 weeks prior to the surgical procedure, and cortisone injection into the shoulder within 6 months prior to the procedure.
All patients received a general anesthetic and 2 g of intravenous cefazolin at induction prior to skin preparation and draping. The surgical site was prepared with a Betadine-alcohol skin preparation antiseptic, equivalent to 10% povidone-iodine solution and 30% ethyl alcohol
From each of 40 patients (25 female patients and 15 male patients) having primary shoulder arthroplasty they submitted 5 swabs from: (1) the subdermal layer, (2) the tip of the surgeon’s glove, (3) the inside scalpel blade (used for deeper incision), (4) the forceps, and (5) the outside scalpel blade (used for the skin incision).
The time to positivity ranged from 4 to 10 days. Seventeen (55%) of the 31 specimens that grew P. acnes had growth by day 5, 7 specimens (23%) had growth by day 8, and 7 specimens (23%) had growth between 9 and 10.25 days.
They concluded that Propionibacterium commonly contaminates the surgical field in primary shoulder arthroplasty. The subdermal layer may be the source of this contamination. Propionibacterium is likely to be spread throughout the surgical field from the subdermal layer via soft-tissue handling by the surgeon and instruments.
Swabs were inoculated onto blood agar, prereduced blood agar, and chocolate agar plates. Specimens were incubated at 37C under 5% carbon dioxide aerobic conditions and anaerobic conditions for 14 days. Organisms grown were identified with initial Gram stain and matrix-assisted laser desorption/ionization time-of-flight (MALDI-ToF) mass spectrometry.
Thirteen (33%) of the 40 patients had at least 1 culture specimen positive for P. acnes.
Two (8%) of the 25 female patients while 11 (73%) of the 15 male patients had ≥1 culture specimen positive for P. acnes.
The most common site of growth of Propionibacterium was the subdermal layer (12 positive samples), followed by the forceps (7 positive samples), the tip of the surgeon’s glove (7 positive samples), the outside scalpel blade (4 positive samples), and the inside scalpel blade (1 positive sample).
27 of 75 swabs that were positive on culture for Propionibacterium in male patients compared with 4 of 125 swabs in female patients; male patients had 66 times higher odds of having a positive culture indicating subdermal colonization compared with female patients (p < 0.001).
The authors acted on the results of these cultures: the 6 patients with 3 positive cultures were empirically treated with oral amoxicillin (or clindamycin in case of penicillin allergy) for 6 weeks, as they were deemed at high risk of developing a postoperative infection.
None of the patients in this study showed evidence of infection within 6 months of surgery.
One patient having two positive cultures for Propionibacterium at the primary surgery had a revision procedure to remove a prominent suture. The suture removed at the revision procedure was culture positive for Propionibacterium.
They concluded that Propionibacterium commonly contaminates the surgical field in primary shoulder arthroplasty. The subdermal layer may be the source of this contamination. Propionibacterium is likely to be spread throughout the surgical field from the subdermal layer via soft-tissue handling by the surgeon and instruments.
Comment: There are two major conclusions that can be drawn from this work.
First, the reported rates of positive cultures at the time of revision arthroplassty may be falsely high as a result of specimen contamination from the dermis at the time of revision. In our practice we strive to avoid this contamination by protecting the tissue samples and explants harvested at the time of revision from contact with the skin. Each tissue sample is obtained with a previously unused sterile rongeur.
Second and more importantly, conventional means of prophylaxis and surgical technique do not prevent the introduction of Propionibacterium into arthroplasty wounds. The fact that some of the swabs were recognized as culture positive within as few as four days indicates that the bacterial load in the sample was large. Taking this result, surgeons and patients need to recognize the reality of wound contamination with Propionibacterium from the sebaceous glands transected at each arthroplasty (and each shoulder procedure) , especially in male patients. This risk remains in spite of standard skin preparation (see this link). The introduction of Propionibacterium into the oxygen poor environment of the medullary canal along with a titanium alloy stem sets up the perfect incubator for the formation of an enduring, bacteria-containing, antibiotic-resistent biofilm on the surface of the implant (see this link). As shown in the present study and others, antibiotic prophylaxis and standard wound preparation does not prevent wound contamination with Propionibacterium.
So what can be done? First, we try to minimize contact of instruments, gloves and implants with the Propionibacterium-containing dermis by applying a Vancomycin impregnated sponge around the periphery of the wound as shown by the arrows in the diagram below.
Second, we try to reduce the number of bacteria in the field prior to implant insertion by copious irrigation with at least 3 liters of antibiotic-containing saline solution, following the adage that 'dilution is the solution to pollution'.
Finally, we apply topical antibiotics (Vancomycin) down the medullary canal just prior to humeral implant insertion in an attempt to 'sterilize the incubator' (see this link). We use additional topical Vancomycin in the wound prior to closure.
Hopefully our long term followup studies will, over time, reveal the effectiveness of these steps.
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