## **Core Concept**
The question pertains to the causes of non-union in femoral neck fractures. Non-union in femoral neck fractures is a significant complication that can arise due to various factors, including the anatomical and physiological characteristics of the femoral neck.

## **Why the Correct Answer is Right**
The correct answer, . or **Poor blood supply**, is a well-established cause of non-union in femoral neck fractures. The femoral neck has a limited and tenuous blood supply, which can be easily disrupted by a fracture. This disruption can lead to inadequate perfusion of the fracture site, impairing the healing process and increasing the risk of non-union.

## **Why Each Wrong Option is Incorrect**
- **Option A:** - This option is not specified, but if it does not relate to the disruption of blood supply or other known causes like **inadequate immobilization**, **infection**, or **poor reduction**, it would be incorrect.
- **Option B:** - Similarly, without specifics, if this option does not accurately describe a cause of non-union, such as **instability of the fracture**, it would be incorrect.
- **Option C:** - If this option does not align with recognized factors contributing to non-union, like **osteoporosis** or **excessive movement at the fracture site**, it would be incorrect.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the **Garden classification** is often used to describe the displacement of femoral neck fractures, and **non-displaced fractures (Garden I and II)** generally have a better prognosis than **displaced fractures (Garden III and IV)**. However, even in non-displaced fractures, the risk of non-union and avascular necrosis remains a concern due to the precarious blood supply.

## **Correct Answer:** . **Poor blood supply**