A 6-month-old baby girl is brought to the ED with a one-day history of emesis and 2 days of loose stools.  She was born full-term without complications, her vaccinations are up-to-date, and she is in daycare most of the day.  The child is diagnosed with acute gastroenteritis, tolerates fluids by mouth, and is discharged home.
 
Five days later, the loose stools have resolved, but mother brings her in again today for recurrent daily emesis and irritability for the past two days.  The baby “felt warm” earlier today.
 
On examination, the child is afebrile and has normal vital signs.  She appears difficult to console and has dry mucous membranes.  The girl cries with exam, and her right knee is warm and tender.  As part of her work-up, you order a radiograph of the affected area:

Which is the next BEST step in her management:
 
    A.    Intravenous access, fluids, laboratory investigation including ESR
    B.    Obtain MRI of the knee for possible periosteal involvement
    C.    CT head non-contrast
    D.    Full septic work-up for possible bacteremia
 
In the meantime, a quote –
 
“In the practice of medicine more mistakes are made from lack of accurate observation and deduction than from lack of knowledge.”
 
– George Howard Bell (1905 - 1986)
Physician and physiologist