Septic arthritis of the Facet Joints (SAFJ) is a rare condition. Little data has been published on the subject. We aimed to describe the clinical, biological and imagery presentations, as well as the course of this rare infection.

We included patients hospitalized between January 1st, 2016 and December 31th, 2019, in the Departments of Infectious Diseases or Rheumatology in 5 French centres in the CRIOGO network. We defined septic arthritis according to Newman's criteria and facet joint arthritis using imagery.

Sixty-five patients were included, predominantly males (64.6%), with a mean age of 68.1 years. The mean time to diagnosis was 25.0 days. The principal symptoms at diagnosis were acute back pain (95.2%) and fever (76.9%). Neurological symptoms were present for 60.7% of the patients, including 16.4% motor deficit or cauda equina syndrome. SAFJ was located on the lumbosacral spine (73.4%) and was rarely multifocal (4.7%). Bacteriological identification was performed by blood cultures in 84.4% of the cases, and the pathogen was mainly Staphylococcus aureus (49.2%). Infective endocarditis was present for 26.9% of patients assessed by echocardiography. On MRI, soft tissue abscess or inflammation, epiduritis and epidural abscess were present in 87.1%, 66.7% and 33.9% of cases, and the pathogen was significantly more frequently Staphylococcus aureus. Mortality reached 9.2%, 18.5% and 23% at one, two, and three years respectively.

SAFJ is a rare but severe disease. Microbiological diagnosis is primarily made on blood cultures, and S. Aureus was the main pathogen. Our results highlight the fact that SAFJ is associated with high morbidity and mortality, and with infective endocarditis.