A 7-year-old boy has a one-week history of leg pains. He wakes up at night and cries because his legs hurt; however, during the day, he feels fine with no pain and no movement limitations. He has no history of trauma, fever, or joint swelling. The family history is negative for rheumatic or collagen vascular disease. The boy’s height and weight are at the 50th percentile for age, he is afebrile, and the physical examination is unremarkable.