After a fall, an older adult is diagnosed with a fracture of the neck of the left femur. What should the nurse practitioner order when the patient reports increased swelling and tightness of the left leg during rehabilitation?

Ordering a venous duplex ultrasound in this scenario is appropriate because it is a non-invasive imaging technique specifically used to evaluate deep vein thrombosis (DVT) or other issues related to venous flow. The symptoms of increased swelling and tightness in the leg after a fracture raise concern for potential complications, such as a DVT, which is not uncommon in older adults following surgeries or prolonged immobility.

The venous duplex ultrasound utilizes high-frequency sound waves to visualize blood flow in the veins and can help detect any clot formation or obstruction. Given the context of an older adult post-fracture, monitoring for DVT is critical, as this condition can lead to serious complications like pulmonary embolism if not addressed promptly.

In contrast, options like arterial Doppler and arteriogram primarily assess arterial circulation, which would not directly help in diagnosing a venous issue. A venous pyelogram is unrelated, as it is used to visualize the urinary tract and would not provide relevant information in the case of leg swelling due to a fracture. Thus, the venous duplex ultrasound stands out as the best choice for evaluating the potential causes of the patient's leg symptoms.