Friday, July 24, 2015

Shoulder arthroscopy has a high rate of positive cultures for Propionibacterium!

The Incidence of Propionibacterium acnes in Shoulder Arthroscopy.

Recognizing that Propionibacterium accounts for the majority of post-shoulder arthroscopy infections, these authors studied 51 patients having outpatient shoulder arthroscopy over a 15-month period. Patients received routine antibiotic prophylaxis (cephalexin, 1 g intravenously) before the procedure.

Initial cultures were obtained before the skin preparation by swabbing the skin at the 3 standard portal sites: posterior, anterosuperior, and anterolateral. Skin preparation was 4% chlorhexidine scrub and 2% chlorhexidine gluconate/70% isopropyl alcohol applied to the entire shoulder. After completion of the arthroscopic procedure, a second culture was obtained through a cannula at the surgical site. Cultures were observed for 21 days using Brucella medium.

Cultures showed a 72.5% Propionibacterium acnes superficial colonization rate: 46.1% of female and 81.6% of male patients (P = .027). The deep culture-positive inoculation rate of 19.6%, all with positive P acnes skin colonization. The average time for cultures to become positive was 12 days. 27% of the shoulders with positive skin cultures had positive deep cultures.

In the discussion, the authors point out, " The difference in P acnes colonization may be attributed to the significantly higher average serum testosterone levels in the male population versus in the female population (270 to 1,070 ng/dL in men v 15 to 70 ng/dL in women). This combined with the established relation between elevated testosterone levels and higher P acnes skin concentrations may account for the difference found between sexes."

The authors suggest that the repeated insertion of instruments and cannulas through the deep
dermis layer of skin may seed the joint with P acnes in all shoulder arthroscopy cases.

The authors have initiated the limited use of benzoyl peroxide skin preparation
in cases of shoulder arthroscopy in hopes of decreasing P acnes  bacterial load on skin.

They also obtain skin swabs in failed arthroscopic and open shoulder cases for the early identification of Propionibacterium.

Comment: Despite standard skin preparation and prophylactic antibiotics, the rate of deep tissue inoculation with Propionibacterium in shoulder arthroscopy was high. Shoulder surgeons must consider the frequency of this inoculation and develop strategies both for minimizing the size of the inoculation and preventing the inoculated bacteria from forming a durable biofilm on implanted suture and implants.