The most common site of fracture neck of femur that causes avascular necrosis is
## **Core Concept**
The question assesses knowledge of orthopedic trauma, specifically the blood supply to the femoral head and its implications for fracture healing. The femoral head receives its blood supply primarily from the medial and lateral circumflex femoral arteries, which give rise to the retinacular arteries. These arteries are crucial for preventing avascular necrosis (AVN) after a femoral neck fracture.
## **Why the Correct Answer is Right**
The correct answer, , is associated with a high risk of avascular necrosis due to the disruption of the blood supply to the femoral head. The blood vessels enter the femoral head at the level of the intertrochanteric line and run along the surface of the femoral neck. A fracture through the mid-portion of the neck (also known as the subcapital region) disrupts these vessels, leading to ischemia and potential AVN of the femoral head. This area is particularly susceptible because the fracture line is close to where the vessels penetrate the bone.
## **Why Each Wrong Option is Incorrect**
* **Option A:** - This region is less commonly associated with AVN compared to the subcapital region because the fracture line is more distal, potentially preserving some of the blood supply to the femoral head.
* **Option B:** - While fractures here can also compromise blood supply, the risk of AVN is generally lower compared to subcapital fractures due to a slightly better preservation of the retinacular arteries.
* **Option D:** - This region is even more distal and has a lower risk of AVN because the blood supply to the femoral head is less likely to be severely compromised.
## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the risk of avascular necrosis increases with the proximity of the fracture to the base of the femoral head. The Garden classification is often used to describe the displacement of femoral neck fractures and correlates with the risk of AVN: the higher the Garden classification (more displaced), the higher the risk of AVN.
## **Correct Answer: .**