Periprosthetic hip infections in a Swedish regional hospital between 2012 and 2018: is there a relationship between Cutibacterium acnes infections and uncemented prostheses?

The purpose of this study was to evaluate patients requiring in-patient care due to a periprosthetic joint infection (PJI), with respect to bacterial agents, surgical treatment, antibiotics, and outcome. We retrospectively identified all infected total hip arthroplasties (THAs) in a Swedish regional hospital during a 7-year period (2012-2018) and reviewed medical records and microbiological data. A total of 89 infected THAs in 87 patients were identified. Standardized treatment with debridement with retention of the implant and antibiotics (DAIR) was initially performed in 53 cases (60 %), one or two stage revisions in 33 cases (37 %), and an immediate Girdlestone in 3 cases (3 %). Infection eradication was seen in 77 PJIs (87 %) in addition to six patients (7 %) ending up with a permanent but uninfected Girdlestone. All six patients with manifest failures were infected with Staphylococcus aureus, two of which were also polymicrobial. Cutibacterium acnes was found in 18 of 89 patients (16 %) distributed in 15 uncemented implants but only in 3 hybrids and cemented arthroplasties, while remaining pathogens were equally distributed in uncemented THAs ( $n=31$ ) and THAs with at least one cemented component ( $n=40$ ; $p=0.003$ ). Eradication was achieved in all 18 patients when Cutibacterium acnes was the only culture ( $n=14$ ) or clearly dominant among positive cultures ( $n=4$ ). DAIR was successful in selected postoperative infections up to 6 months after hip replacement. Cutibacterium acnes infections in hip arthroplasty may be underdiagnosed. Cemented components in THAs seem to protect from colonization with Cutibacterium acnes.