A 45-year-old man is brought to the emergency department in cardiac arrest. The trauma team decides to establish emergency central venous access via the femoral approach. During the procedure, the physician palpates the femoral pulse and attempts to cannulate the artery. However, the needle is inadvertently placed medial to the intended target. The structure marked **C** in the diagram is now at risk of puncture. Which of the following best describes the anatomical relationship that explains this complication?

Explanation

The femoral vein (structure **C**) lies medial to the femoral artery within the femoral triangle. This anatomical relationship is critical during femoral vascular access procedures. The mnemonic NAVEL (Nerve, Artery, Vein, Empty space, Lymphatics) describes the contents of the femoral triangle from lateral to medial. When a physician palpates the femoral pulse (artery) and places a needle medial to this landmark, the femoral vein is the next structure encountered, making it highly vulnerable to inadvertent puncture. This is a common complication during attempted femoral artery cannulation, particularly in emergency settings where time pressure may compromise technique. Understanding this medial relationship is essential for safe femoral vascular access and for recognizing why femoral vein puncture occurs with medial needle placement. (Gray's Anatomy 42e, Ch 80)