A 55-year-old patient with a suspected hip fracture is brought to the emergency department after a motor vehicle accident. Which assessment finding would be MOST indicative of a displaced femoral neck fracture?

External rotation and shortening of the affected leg is the classic presentation of a displaced femoral neck fracture, making it most indicative. Other options are less specific or common in various hip injuries.

Classic Presentation of a Displaced Femoral Neck Fracture

When assessing a patient with a suspected hip fracture following trauma, distinguishing between a non-displaced and a displaced fracture is critical for timely intervention. In a displaced femoral neck fracture, the normal anatomy of the hip is disrupted, leading to a characteristic clinical sign that is highly indicative of the injury.

The assessment finding most indicative of a displaced femoral neck fracture is external rotation and shortening of the affected leg. This classic presentation occurs because the fracture severs the structural continuity between the femoral head and the femoral shaft. The unopposed pull of the iliopsoas muscle and the external rotators (such as the piriformis and obturator muscles) acts on the distal fragment, causing the leg to rotate outward and appear shorter due to the overriding of bone fragments [1,3]. This is a key differentiator from a non-displaced fracture, where the leg may not assume this characteristic deformed position.

The other options represent findings common to many hip injuries but lack the specificity for a displaced fracture. Pain that increases with weight-bearing is a hallmark of any fracture, and bruising and swelling are typical signs of soft tissue trauma and bleeding, which can occur with or without displacement. Similarly, limited range of motion is expected due to pain and mechanical instability in any type of femoral neck fracture. However, the combination of external rotation and a visibly shortened limb is a direct mechanical consequence of the displacement, making it the most specific and urgent finding that points toward the diagnosis of a displaced fracture, a condition associated with a high risk of complications like avascular necrosis and nonunion [1,2].