Does fluid irrigation in arthroscopic shoulder biopsy affect sensitivity of Cutibacterium acnes cultures for prosthetic shoulder joint infections?

Background: Cutibacterium acnes is the most common infectious agent in shoulder periprosthetic joint infection. Culture-based detection from tissue biopsy is the current gold standard for diagnosis, but the methods used to obtain it may affect accuracy of biopsies. The objective of this study is to investigate the impact of shoulder arthroscopy irrigation on culture-based detection from tissue biopsy samples for suspected C. acnes colonization in the setting of a periprosthetic total shoulder infection. Methods: An in vitro model was designed to hold Gelfoam inoculated with a standard inoculum of C. acnes. Sterile sampling was performed in simulation of arthroscopic practice, both with and without saline irrigation being applied. All biopsies were subsequently incubated under anaerobic conditions in broth media and monitored for visible growth over the course of 14 days. Results: Sixty samples were collected for the no-irrigation group and 60 samples were collected for the irrigation group. A total of 19 biopsies (32%) in the no-irrigation group resulted in positive C. acnes growth within two weeks of initial culturing, compared to 14 positive biopsies (23%) in the irrigation group (P = .310). No significant differences resulted between the no-irrigation and irrigation groups at each evaluated time point (0-2 days, 3-7 days, 8-14 days). Conclusion: In the context of our model, irrigation during shoulder arthroscopy did not significantly impact recovery of C. acnes using culture-based methods in the setting of shoulder periprosthetic joint infections.