You are answering a USMLE-style medical question. Question: A 13-year-old boy presents to the emergency department with severe knee, hip, and groin pain. The patient has a past medical history notable only for obesity and asthma. His temperature is 98°F (36.7°C), blood pressure is 124/65 mmHg, pulse is 128/min, respirations are 14/min, and oxygen saturation is 99% on room air. Physical exam is notable for an inability of the patient to bear weight on his left leg and limited range of motion of the left hip. Which of the following is the best management for this patient? Options: A) Casting and crutches B) Immobilization of the hip in a Pavlik harness C) Supportive therapy and observation D) Surgical pinning of the femoral head Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.