A 32-year-old man presents to the emergency department 6 hours after a motor vehicle accident with a closed fracture of the right femur. On examination, he is alert, blood pressure 110/70 mmHg, heart rate 98/min, respiratory rate 18/min. The right thigh is swollen and tense. Urine dipstick shows 3+ blood with no RBCs on microscopy. Serum creatinine is 1.2 mg/dL (baseline 0.9 mg/dL). What is the most likely diagnosis explaining the dipstick finding?