An evidence-based approach to managing unexpected positive cultures in shoulder arthroplasty
Alexander J. Hodakowski MD; Matthew R. Cohn MD; Nabil Mehta MD; Mariano E. Menendez MD; Johnathon R. McCormick MD; Grant E. Garrigues MD
Review article · Volume 31, Issue 10, Pages 2176–2186, October 2022
Background
The question this review asked
Surgeons routinely send intraoperative cultures during shoulder replacement to rule out periprosthetic joint infection, and those cultures often come back positive in patients showing no clinical or radiographic sign of infection at all. Cutibacterium acnes is widely assumed to be the organism most often responsible in this setting, but what an unexpected positive result actually means is neither clearly defined nor agreed upon across the literature. This review set out to establish how frequently unexpected positive cultures and C acnes appear, what clinical significance they carry, and which factors influence either their frequency or a patient's recovery if infection does develop.
Methods
How the review was conducted
The authors ran a systematic review following PRISMA guidelines, searching the PubMed, CINAHL, and Scopus databases. Studies published between January 1, 2000 and May 20, 2021 were eligible if they specifically reported on unexpected positive cultures in native or revision shoulder surgery, or directly addressed one of six questions the authors defined in advance. Twenty-two studies met the inclusion criteria.
Results
What the evidence showed
Across 2,373 patients, deep tissue specimens returned unexpected positive cultures at a pooled rate of 27.5 percent, or 653 of 2,373 specimens. C acnes accounted for 76.4 percent of those positive specimens. Three studies reported positivity on inanimate specimens at a pooled rate of 20.1 percent. Male patients were more likely to have an unexpected positive culture, while findings on prior surgery, surgical approach, and type of surgery conflicted across articles. Patient-reported outcomes and reoperation rates showed no difference between patients with positive cultures and those without, and although antibiotic use and treatment regimens varied widely across studies, reinfection rates did not differ significantly between them.
Conclusion
What it means
Unexpected positive cultures are a common finding in shoulder surgery, and C acnes makes up the largest share of what gets cultured. Preoperative risk factors, surgical technique, and postoperative treatment regimens did not meaningfully change how often these cultures appeared or how patients fared afterward. A standardized protocol for treatment and follow-up would remove much of the uncertainty surgeons face when a culture comes back positive. On the strength of this review, shoulder surgeons can consider leaving the postoperative course largely unchanged when an unexpected positive culture appears with no other evidence of periprosthetic joint infection.
