**Core Concept**
The treatment of choice for a fracture neck of femur, particularly in a delayed presentation of 3 days, involves a balance between anatomical reduction, stable fixation, and early mobilization. This requires a deep understanding of orthopedic principles and the potential complications associated with delayed treatment.

**Why the Correct Answer is Right**
The treatment of choice is **closed reduction and percutaneous pinning**. This involves manually reducing the fracture under fluoroscopic guidance, followed by percutaneous pinning to maintain the reduction and promote healing. This approach is advantageous in the early phase, as it allows for early mobilization and minimizes the risk of complications such as avascular necrosis.

* The rationale behind this approach is to restore the anatomical alignment of the femoral neck, which is crucial for preventing further complications and ensuring proper healing.
* The use of percutaneous pinning provides a stable fixation, allowing for early mobilization and reducing the risk of deep vein thrombosis and pressure sores.

**Why Each Wrong Option is Incorrect**
**Option A:** **Open reduction and internal fixation (ORIF)** may be considered in cases where closed reduction is not feasible, but it carries a higher risk of complications and requires a longer hospital stay.
**Option B:** **Non-operative management** is not suitable for a fracture neck of femur, as it may lead to malunion, avascular necrosis, and other complications.
**Option C:** **Arthroplasty** is typically reserved for cases where the fracture is comminuted or the patient has significant co-morbidities, and is not the initial treatment of choice for a straightforward fracture neck of femur.

**Clinical Pearl / High-Yield Fact**
In cases of delayed presentation, it is essential to assess the patient's overall condition and any potential complications that may have arisen, such as avascular necrosis or malunion.

**Correct Answer:** A. Closed reduction and percutaneous pinning