Friday, March 30, 2018

Predicting the presence of Propionibacterium in the freshly incised dermis In primary shoulder arthroplasty.

Preoperative Skin-Surface Cultures Can Help to Predict the Presence of Propionibacterium in Shoulder Arthroplasty Wounds 

Propionibacterium species are commonly cultured from specimens harvested at the time of revision shoulder arthroplasty. These bacteria reside in normal sebaceous glands, out of reach of surgical skin preparation. The arthroplasty incision transects these structures, which allows Propionibacterium to inoculate the wound and to potentially lead to the formation of a biofilm on the inserted implant. To help identify patients who are at increased risk for wound inoculation, these authors investigated whether preoperative cultures of the specimens from the unprepared skin surface were predictive of the results of intraoperative cultures of dermal wound-edge specimens obtained immediately after incision of the surgically prepared skin.

Sixty-six patients (mean age, 66.1 ± 9.4 years [range, 37 to 82 years]; 73% male) undergoing primary shoulder arthroplasty had preoperative cultures of the unprepared skin surface and intraoperative cultures of the freshly incised dermis using special culture swabs.

For the first 50 patients, a control swab was opened to air during the same time that the dermal specimen was obtained.

The results for female and male patients were characterized as the Specimen Propionibacterium Value (SpPV). The authors then determined the degree to which the results of cultures of the skin surface specimens were predictive of the results of culture of the dermal specimens.

An example of this semiquantitative reporting is shown below for the 21-day cultures of specimens from a 42-year-old man who presented for a primary shoulder arthroplasty.
Fig. 1-A Results of the culture of a specimen from the unprepared skin surface. Combining the culture positivity for the 2 different species of Propionibacterium yielded an SpPV of 2.
Note that, despite the presence of these bacteria, the Gram smear was negative.
Fig. 1-B Results of the culture of a specimen from the freshly incised dermis. The SpPV was 3.
Fig. 1-C Results of the culture of the control swab. TheSpPVwas 0.

Results: The skin-surface SpPV was greater than 1 in 3 (17%) of the 18 female patients and in 34 (71%) of the 48 male patients (p <0.001).

The dermal SpPV was greater than 1 in 0 (0%) of the 18 female patients and in 19 (40%) of the 48 male patients (p < 0.001).

None of the control samples had an SpPV greater than 1.   The predictive characteristics of a skin-surface SpPV of greater than 1 for a dermal SpPV of greater than 1 were as follows: sensitivity, 1.00 (95% confidence interval [CI], 0.82 to 1.00); specificity, 0.62 (95% CI, 0.46 to 0.75); positive predictive value, 0.51 (95% CI, 0.34 to 0.68); and negative predictive value, 1.00 (95% CI, 0.88 to 1.00).

The authors concluded that preoperative culture of the unprepared skin surface can help to predict whether the freshly incised dermal edge is likely to be positive for Propionibacterium. This test may help to identify patients who may merit more aggressive topical and systemic antibiotic prophylaxis.

Comment: This study shows (1) the the freshly incised dermis is often culture positive for Propionibacterium in spite of surgical skin preparation for shoulder arthroplasty,  (2) that surgeons have the opportunity to use preoperative skin cultures to determine the likelihood that the shoulder arthroplasty wound will be culture-positive for Propionibacterium, and (3) the value of taking control cultures to assess the possibility of contamination in each operating room.

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