Question

During a health maintenance visit, a $13$-year-old adolescent male reports a $4$-week history of a constant, dull ache in his left anterior thigh and knee. He has no history of recent trauma, fever, or prior medical conditions. His body mass index is $32 \text{ kg/m}^2$. Vital signs are within normal limits, with a temperature of $36.8^\circ\text{C}$ ($98.2^\circ\text{F}$), heart rate of $78/\text{min}$, and blood pressure of $112/72 \text{ mm Hg}$. On physical examination, the left knee has no effusion, erythema, or joint line tenderness, and range of motion is full and painless. However, his gait is noticeably antalgic, and his left foot rests in an externally rotated position while standing. Passive internal rotation of the left hip is restricted and elicits pain. Laboratory evaluation reveals an erythrocyte sedimentation rate of $9 \text{ mm/h}$, a C-reactive protein level of $0.4 \text{ mg/dL}$, and a leukocyte count of $7,100/\text{mm}^3$. Which of the following is the most appropriate next step in management?