Question

An $11$-year-old girl is brought to the outpatient pediatric clinic by her father due to an $8$-week history of right-sided distal thigh and knee pain. The pain is described as a dull ache that worsens with physical activity, particularly after her dance classes, and improves with rest. She has not experienced any preceding trauma, fever, chills, or weight loss. Her past medical history is unremarkable, and she takes no medications. Vital signs show a temperature of $37.0^\circ\text{C}$ ($98.6^\circ\text{F}$), heart rate of $78/\text{min}$, and blood pressure of $112/68 \text{ mm Hg}$. Her body mass index (BMI) is $28.5 \text{ kg/m}^2$ (above the $95^{\text{th}}$ percentile for age). Physical examination reveals a well-appearing girl walking with an antalgic gait. Inspection of the right knee shows no erythema, effusion, or localized tenderness over the tibial tuberosity or joint line. Ligamentous and meniscal testing of the knee is normal. When the patient is placed in the supine position and the right hip is passively flexed, the thigh deviates into obligatory external rotation. Internal rotation of the right hip is limited and elicits discomfort. Laboratory studies reveal a leukocyte count of $7,200/\text{mm}^3$, an erythrocyte sedimentation rate of $8 \text{ mm/h}$, and a C-reactive protein level of $0.3 \text{ mg/dL}$. Which of the following is the most appropriate next step in management?