Cutibacterium acnes Culture Isolation Following Total Hip and Total Knee Arthroplasty

Introduction: Cutibacterium acnes, a component of normal skin flora and a common commensal Gram-positive bacterium, presents a diagnostic challenge for arthroplasty surgeons. While Cutibacterium acnes (C. acnes) as a source of infection has been well characterized in shoulder surgery, its presentation and clinical significance in total hip (THA) and total knee arthroplasty (TKA) remain less understood. Methods: A retrospective chart review identified patients with C. acnes culture positivity following THA or TKA. Demographics, laboratory values, and microbiologic data were collected. Statistical comparisons were performed using t-tests and chi-squared analysis. One-year outcomes were evaluated using the Musculoskeletal Infection Society Outcome Reporting Tool (MSIS ORT) criteria among patients undergoing further surgical intervention. Results: Twenty-nine patients with C. acnes-positive cultures were identified (21 THA, 8 TKA); 15 (52%) were polymicrobial. Ten THA patients (47.6%) and seven TKA patients (87.5%) met MSIS criteria for infection at the time of presentation. Mean time to culture positivity was similar between THA (6.8 days) and TKA (7.4 days; p = 0.57). Sonicated cultures were positive in 24% of THA and 12.5% of TKA cases. Mean ESR was 36.4 mm/h for THA and 51.5 mm/h for TKA (p = 0.21); mean C-reactive protein (CRP) was 35.2 and 36.8 mg/dL, respectively (p = 0.95). Mean synovial cell counts were 27,055 for THA and 22,194 for TKA, with polymorphonuclear cells (PMN) percentages of 68% and 73.9% (p = 0.72, 0.70). Monomicrobial infections demonstrated a mean cell count of 24,143 with 58.9% PMNs, compared to 25,903 and 78.8% in polymicrobial cases. At one year, 72% of patients undergoing subsequent surgery achieved successful outcomes. Higher ASA classification was the only significant predictor of failure (mean 3.0 vs. 2.75). Conclusions: C. acnes-associated THA and TKA infections often present with delayed culture growth, mild inflammatory markers, and frequent polymicrobial involvement. At one-year, patients with available follow-up who undergo surgical management experience favorable outcomes, with 72% achieving MSIS ORT success.