LAUSR

BACKGROUND Culturing of deep tissues obtained at revision arthroplasty for Cutibacterium is a key component of diagnosing a periprosthetic infection. The value of culturing explanted components has not been well-described. This study sought to answer the following questions: 1) How does the culture positivity of explant cultures compare to that of deep tissue cultures? 2) How often are explant cultures positive when tissue cultures are not, and vice versa? 3) How does the bacterial density in explant cultures compare to that in tissue cultures? METHODS 106 anatomic arthroplasties revised over a 7-year period were included. Explant (humeral head, humeral stem, glenoid) and tissue (collar membrane, humeral canal tissue, periglenoid tissue) specimens were sent for semiquantitative Cutibacterium culture. We compared culture positivity and bacterial density when cultures of an explant and tissue adjacent to the implant were both available. RESULTS Explants had positive cultures at a higher rate than adjacent tissue specimens for most anatomic sites. Of the shoulders that had Cutibacterium growth, a higher proportion of explants were culture positive when tissue samples were negative (23-43%) than vice versa (0-21%). The Cutibacterium density was higher in explants than in tissues. Considering only the results of tissue samples, 16% of the shoulders met our threshold for infection treatment (≥2 positive cultures; however, with the inclusion of the results for explant cultures additional 14% of cases - a total of 30% - met the criteria for infection treatment. CONCLUSIONS In this group of patients, culturing explants in addition to tissue cultures increased the sensitivity for detecting Cutibacterium in revision shoulder arthroplasty. LEVEL OF EVIDENCE Basic Science Study; Microbiology.