The median cubital vein is a short oblique communicating vein in the antecubital fossa that connects the cephalic vein laterally to the basilic vein medially, crossing over the bicipital aponeurosis (lacertus fibrosus). It is the most commonly used site for venepuncture and intravenous cannulation worldwide due to its consistent location, large calibre, and superficial position.
The bicipital aponeurosis (lacertus fibrosus) lies immediately deep to the median cubital vein, separating it from the brachial artery and median nerve. This fascial layer protects the artery during venepuncture but also means that injections given too deeply, or arterial access mistaken for venous, will reach the brachial artery. Inadvertent intra-arterial injection of irritant substances causes devastating arterial spasm, thrombosis, and forearm compartment syndrome. The vein's position can vary, and its absence requires use of the cephalic or basilic veins directly.
A misplaced antecubital line that penetrates the bicipital aponeurosis and enters the brachial artery rather than the median cubital vein produces pulsatile bright-red backflow; injection of irritants causes severe forearm ischaemia requiring emergency vascular surgery.
Repeated venepuncture or IV cannula at the median cubital vein produces superficial thrombophlebitis with tenderness and a cord-like palpable vein, managed conservatively with warm compresses and NSAIDs.
