A 25-year-old patient is brought into the emergency department after he was found down by the police in 5 degree celsius weather. The police state the patient is a heroin-user and is homeless. The patient's vitals are T 95.3 HR 80 and regular BP 150/90 RR 10. After warming the patient, you notice his left lower leg is now much larger than his right leg. On exam, the patient has a loss of sensation on his left lower extremity. There is a faint palpable dorsalis pedal pulse, but no posterior tibial pulse. The patient is unresponsive to normal commands, but shrieks in pain upon passive stretch of his left lower leg. What is the most probable cause of this patient's condition?