While a 20-year-old woman was being chased by an assailant, she tripped on railroad tracks, fell, and felt immediate pain in her left knee. As the pain led to loud screaming, the assailant fled. The emergency medical service brought the patient to a level 1 trauma center. The patient was awake and alert with normal vital signs. She was unable to move her left knee, which appeared to be dislocated. Although she had sensation in the left foot and limited movement of the left ankle and toes, there were no palpable distal pulses or Doppler signals. The most appropriate first step in the management of this patient is: 1. Left below-knee four-compartment fasciotomy. 2. CT arteriography. 3. Administration of unfractionated heparin. 4. Operative exploration. In consultation with the trauma attending surgeon, the trauma fellow administered intravenously 5000 units of unfractionated heparin in light of the probable complete occlusion of the popliteal artery and the lack of an open wound or other major associated injuries. Orthopedic surgery agreed that the patient had a posterior dislocation of the left knee with probable injury to the mid-left popliteal artery (figure 1). The dislocation was successfully reduced under intravenous sedation. No pulsations were noted in the left pedal arteries after the reduction. Figure 1 Posterior dislocation of the left knee joint. The most appropriate next step in the management of this patient is: 1. Left below-knee four-compartment fasciotomy. 2. CT arteriography. 3. Administration of aspirin (ASA) 181 mg. 4. Contact the endovascular surgeon. A one-shot left femoral arteriogram (patient cared for before availability of CT arteriography) documented a thrombosis in the left mid-popliteal artery (figure 2). Figure 2 Blunt thrombosis of the left popliteal artery behind the knee joint. The patient was typed and crossed for two units of packed red blood cells, received 1 g of cephalosporin antibiotic intravenously, and was moved to the …