<em>Streptococcus mitis</em> septic arthritis after leucocyte-rich platelet-rich plasma injection for the knee osteoarthritis: A case report.

A 62-year-old female patient having comorbidities of hypertension, hyperlipidemia, obesity, peptic ulcer, and bilateral Grade II knee osteoarthritis was admitted with a complaint of knee pain. An intra-articular leukocyte-rich platelet-rich plasma (LR-PRP) injection was administered to both knees after clinical and laboratory examinations. Three days later, the pain increased and synovial effusion developed in her left knee. The patient was diagnosed with Streptococcus mitis-induced septic arthritis. Clinical and laboratory improvement was obtained with immediate ceftriaxone treatment in addition to irrigation and debridement. This is the first case report in the literature describing septic arthritis developing after intra-articular injection LR-PRP injection.