Background: Septic arthritis is an orthopaedic emergency that can lead to significant morbidity and mortality if treatment is delayed. Myositis can present in a similar way to septic arthritis, particularly in a young child, but is treated differently. Clinicians must take both into account when assessing patients.
Case Description: A five-year-old girl presented with a swollen, sore knee on a background of minor trauma. Examination findings revealed severe sepsis, tonsillitis and a florid rash suspicious of scarlet fever. An orthopaedic opinion was requested for the possibility of septic arthritis of the knee. Due to swelling of the thigh, a provisional diagnosis of myositis secondary to Group A Streptococcal throat infection was made and confirmed by MRI scan of the lower leg. The patient was transferred to an intensive care unit for monitoring and antibiotic therapy.
Literature Review: There are reports of myositis being mistakenly diagnosed as septic arthritis of the knee leading to iatrogenic septic arthritis as a result of needle aspiration.
Clinical Relevance: This highlights the diagnostic challenge posed in the case of a young, septic child who presens with a swollen, painful limb. Repeated clinical examination and the judicious use of magnetic resonance scanning assists in this situation.
Joe Littlechild, Faz Alipour
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