[Primary meningococcal infection of the knee. A rare cause of septic arthritis].

This article presents a case of primary septic arthritis of the knee due to serogroup C Neisseria meningitidis. A 19-year-old female presented to the emergency department with a painless but swollen knee joint which had started 2 days previously and fever (38 °C). The patient reported that she suddenly felt unwell 3 days ago and developed a rush at the same time which had almost disappeared when arrived at the emergency department. The patient was admitted to hospital and an antibiotic therapy was started with sulbactam and ampicillin. Initially, incubation of synovial fluid over the next 3 days did not result in detection of any pathogens; therefore, a reactive arthritis was assumed until Neisseria meningitidis was detected in cultures of the synovial fluid. Therapy was then switched to antibiotic therapy with ceftriaxon and arthroscopic irrigation was performed. The patient quickly recovered and was discharged from hospital after 14 days. This case example shows the difficulties of the clinical and microbiological diagnostics of a primary septic meningococcal arthritis; however, the treatment is relatively easy and mostly successful compared to other forms of bacterial joint infection.