Clinical Challenge: Left Knee Pain in Toddler

History of Present Illness

A toddler is brought to the hospital with bilateral knee pain, which is significantly worse on the right side. According to his mother, 2 weeks ago the child was placed on amoxicillin for an ear infection and on the last day of antibiotics he developed a rash on both of his legs. Soon after developing the rash, the boy started to develop swelling and pain affecting both knees. His pediatrician then started him on prednisone for 5 days and the knee pain improved. However, a week after finishing the prednisone, he began limping. On waking this morning, he was in a curled-up position and refused to walk or stand. His mother notes that her son has no fever, injury, or other symptoms.

Vital Signs & Physical Examination

The patient’s vital signs are normal. Physical examination is also normal except that the child kept both knees flexed and refuses to walk. There is no redness, swelling, or warmth to either knee and no visible rash. Laboratory tests were normal, including Chem-7, and radiographs of the knees are normal. The mother took pictures of the rash when it occurred (Figures).