Pseudoparalysis of the lower extremity in an infant

We describe a case of septic arthritis of the knee in an afebrile, well-appearing four-month-old female. She had been evaluated previously for lower extremity disuse attributed to antecedent trauma. Her physical examination was remarkable only for limitation of extension of the affected leg at the knee. Emergency physicians should understand the physical examination findings suggesting joint effusion and the need to consider osteomyelitis/septic arthritis in children less than one year of age with pseudoparalysis.