Pediatric Septic Arthritis of the Knee due to Fusobacterium necrophorum in a Patient with Down Syndrome

A 16-year-old boy with a history of Down syndrome presented with right knee pain and swelling. He was diagnosed with isolated septic arthritis of the knee due to Fusobacterium necrophorum in the absence of current or recent oropharyngeal infection. He was successfully treated with arthroscopic irrigation and debridement and 12 weeks of oral antibiotics.Fusobacterium necrophorum is a part of the normal oral flora and a rare cause of septic arthritis, typically associated with recent oropharyngeal infection. However, patients with immune dysregulation such as those with Down syndrome may develop isolated septic arthritis due to transient hematogenous seeding.