<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 3-year-old patient is brought to the emergency department by her mother due to inability to walk. The child has been limping recently and as of this morning, has refused to walk. Any attempts to make the child walk or bear weight result in crying. She was recently treated for impetigo and currently takes a vitamin D supplement. Physical exam is remarkable for an anxious appearing toddler with knee swelling, erythema, and limited range of motion due to pain. Her mother denies any recent trauma to the childs affected knee. Temperature is 103F 39.4C, pulse is 132min, blood pressure is 9050 mmHg, respirations are 18min, and oxygen saturation is 99 on room air. Which of the following is the best initial step in management?? A: Radiograph, B: MRI, C: Ultrasound, D: Broad spectrum antibiotics, E: Synovial fluid analysis,  <response>: Based on the information provided in the question stem, this appears to be a case of a 3-year-old child presenting with acute knee pain, swelling, erythema, fever, and inability to bear weight, suggesting an inflammatory process affecting the knee joint. There is no history of recent trauma. The description is most consistent with septic arthritis given the acute presentation in a young child. The next step in management would be to perform a diagnostic procedure to confirm the diagnosis and identify the causative organism to guide antibiotic therapy. Of the options provided, synovial fluid analysis would allow for evaluation of white blood cell count, gram stain, and culture of the joint fluid to confirm septic arthritis and identify the organism. Radiograph may show joint effusion but does not provide information about the causative organism. MRI would provide imaging of the joint but is more costly and does not provide information about the organism. Ultrasound could evaluate for joint effusion but does not allow for synovial fluid analysis. Broad spectrum antibiotics may be indicated for treatment but a definitive diagnosis should be made first to guide appropriate antibiotic selection.E: Synovial fluid analysis 