**Question:** A 30-year-old man had a road traffic accident and sustained a fracture of the femur. Two days later, he developed sudden breathlessness. The most probable cause can be -

A. Pulmonary contusion
B. Pulmonary embolism
C. Pulmonary contusion and pulmonary edema
D. Pulmonary contusion and pneumothorax

**Core Concept:**

In the context of a patient with a femur fracture, sudden onset breathlessness could indicate complications related to the trauma or the underlying medical condition. Fracture of the femur often leads to immobilization and subsequent muscle atrophy, which can lead to decreased lung compliance, making the patient more prone to respiratory compromise.

**Why the Correct Answer is Right:**

The correct answer is B (Pulmonary embolism). Pulmonary embolism occurs when a blood clot (embolus) travels from the lower extremity veins (e.g., deep vein thrombosis) to the lungs, causing blockage and subsequent hypoxia. In this case, the patient already has a femur fracture and immobilization, which increases the risk of deep vein thrombosis. The sudden onset of breathlessness two days post-trauma suggests the development of a pulmonary embolism, leading to respiratory distress.

**Why Each Wrong Option is Incorrect:**

A. Pulmonary contusion: Although a pulmonary contusion can occur due to the trauma, the sudden onset of breathlessness two days after the injury is unlikely to be solely due to a contusion, as contusions usually present acutely.

C. Pulmonary contusion and pulmonary edema: While the combination of pulmonary contusion and edema is possible, the sudden onset of breathlessness two days post-injury is more consistent with pulmonary embolism.

D. Pulmonary contusion and pneumothorax: Pneumothorax can occur with a fractured rib, but the sudden onset of breathlessness two days after the injury is less likely due to this combination. Additionally, the patient already has a femur fracture, which increases the risk of deep vein thrombosis, rather than pneumothorax.

**Clinical Pearl:**

In patients with femur fractures and immobilization, it is essential to actively screen for and manage the risk of deep vein thrombosis and pulmonary embolism. Management may involve anticoagulation therapy and early mobilization of the patient to prevent these serious complications.