A 52-year-old woman from Mumbai presents with acute right hip pain following a fall on an icy pavement. She is unable to bear weight and the right lower limb is held in flexion, adduction, and internal rotation. On examination, the right leg appears shortened compared to the left. Plain radiograph confirms a displaced intracapsular fracture of the femoral neck. During surgical planning, the orthopedic surgeon is concerned about potential avascular necrosis (AVN). Which anatomical feature of the femoral neck blood supply makes intracapsular fractures particularly prone to AVN?