Propionibacterium acnes Host Inflammatory Response During Periprosthetic Infection Is Joint Specific

Background: Propionibacterium acnes (P. acnes) has become increasingly recognized as a cause of periprosthetic joint infection (PJI). Questions/Purposes: It is not currently known if the clinical presentation of P. acnes varies depending on the joint being infected. Methods: We retrospectively reviewed patients infected with P. acnes after total hip, knee, and shoulder arthroplasty from two institutions. Patients were classified as having a PJI based on the Musculoskeletal Infection Society criteria and were excluded if they had a polymicrobial culture. Patient demographics, preoperative laboratory values, and microbiology data were analyzed. Results: Eighteen knees, 12 hips, and 35 shoulders with a P. acnes PJI were identified. Median ESR was significantly higher in the knee (38.0 mm/h, IQR 18.0–58.0) and hip (33.5 mm/h, IQR 15.3–60.0) groups compared to the shoulder group (11.0 mm/h, IQR 4.5–30.5). C-reactive protein levels were higher in the knee (2.0 mg/dl, IQR 1.3–8.9) and hip (2.4 mg/dl, IQR 0.8–4.9) groups compared to the shoulder group (0.7 mg/dl, IQR 0.6–1.5). Median synovial fluid WBC was significantly higher in the knee group than shoulder group (19,950 cells/mm³, IQR 482–60,063 vs 750 cells/mm³, IQR 0–2825, respectively). Peripheral blood WBC levels were similar between groups, as was mean time of P. acnes growth in culture. Clindamycin resistance was present in all groups. Conclusion: The manner in which a patient with P. acnes PJI presents is joint specific. Inflammatory markers were significantly higher in the knee and hip groups compared to the hip and shoulder groups, and long hold anaerobic cultures up to 14 days are necessary to accurately identify this organism.