• Nathalie Pruijn, Floor M van Diek, Jacques F Meis, Nienke M Kosse, and Oscar Dorrestijn.
• Sint Maartenskliniek Research, Sint Maartenskliniek, Nijmegen, The Netherlands.
• Arch Orthop Trauma Surg. 2021 Feb 1; 141 (2): 197-205.

IntroductionLow-grade Cutibacterium acnes (C. acnes) infections after shoulder surgery usually result in unexplained complaints. The absence of clinical signs of infection makes the incidence unclear and underreported. This study aimed to determine the incidence of C. acnes infections in patients with artificial material and unexplained persistent shoulder complaints. We hypothesized that the incidence of C. acnes infections would be higher in patients with artificial material. Risk factors and associations between culture time and contaminations/infections were also assessed.Materials And MethodsThis retrospective cohort study included patients with and without artificial material undergoing revision shoulder surgery for persistent complaints after primary surgery and the suspicion of a low-grade infection. Three-six cultures were taken in all patients. C. acnes infection incidence was determined and logistic regression analysis was performed to identify risk factors. The association between time to culture growth and infections/contaminations was evaluated using Kaplan-Meier analysis and log-rank test.Results26/61 (42.6%) patients with and 14/33 (42.2%) without material had a C. acnes infection. Age (OR 0.959; 95% CI 0.914-1.000) and BMI (OR 0.884; 95% CI 0.787-0.977) were risk factors. Time to C. acnes culture positivity was not different between infections and contaminations.ConclusionThe incidence of C. acnes infections was 42.6% in patients with artificial material and 42.2% in patients without artificial material. Younger age and lower BMI are risk factors. Low-grade C. acnes infections should be considered in patients with unexplained persistent complaints following shoulder surgery.

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