These authors cultured nonabsorbable, braided, subscapularis tagging sutures in 50 consecutive patients undergoing primary shoulder arthroplasty. A similar nonabsorbable, braided suture (control) was placed in a sterile container on the back table, open to the operating room environment.
The subscapularis tagging sutures and control sutures were collected prior to subscapularis tenotomy repair and submitted for aerobic and anaerobic cultures. Cultures were observed for 21 days
A total of 12 of 50 experimental and 16 of 50 control sutures had positive cultures. Staphylococcus epidermidis and Cutibacterium acnes were the 2 most commonly isolated organisms. No significant association between positive subscapularis tagging suture cultures and positive control cultures was found.
Comment: It is difficult to know how to interpret this study in which the "control" cultures were positive at a higher rate than the "experimental" cultures. What then is the meaning of a positive experimental culture? It surely points out the need for investigators to know the results of control cultures in their OR and lab. From this study, we cannot know if the control cultures were contaminated in the package, in the OR, in transit or in the lab.
Another possible interpretation is that all the instruments, implants and sutures exposed in the OR are at risk for contamination and expose the arthroplasty to infection.
The reporting of cultures as being simply "positive" or "negative" for the different organisms does not indicate the load (amount) of bacteria in the specimen.
We find that the understanding of culture results is enhanced by the use of semiquantitative methods to assess the load of bacteria in each specimen. 68% of the patients in this study were female; it is known that Cutibacterium skin levels are much higher in males.
Compare the study below in which "control" cultures were found to have very low loads of bacteria.
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, we 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). We 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.
The skin-surface SpPV was ≥1 in 3 (17%) of the 18 female patients and 34 (71%) of the 48 male patients (p < 0.001). The dermal SpPV was ≥1 in 0 (0%) of the 18 female patients and 19 (40%) of the 48 male patients (p < 0.001). None of the control samples had an SpPV of ≥1. The predictive characteristics of a skin-surface SpPV of ≥1 for a dermal SpPV of ≥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).
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