Anatomy of Volkmann ischemia. A, “Collateral circulation” of elbow does not communicate with vessels within flexor compartment. These elbow collaterals join radial and ulnar arteries proximal to pronator teres, the proximal guardian of flexor compartment. B, Brachial artery and median nerve enter forearm through tight opening formed by biceps tendon insertion laterally and pronator teres muscle medially and are tightly covered by lacertus fibrosus. Proximal angulation, hematoma, or muscle swelling within this cruciate tendon-muscle portal is capable of major compression of neurovascular bundle. C, Radial artery, arising from brachial artery, passes distally superficial to pronator teres and all flexor muscles. It is not crossed by any structure along this route. Ulnar artery passes beneath pronator teres and lies in deepest portions of compartment. Median nerve usually passes between humeral and ulnar heads of fleshy pronator teres, and, emerging, it becomes compressed against firm arcuate band of flexor sublimis origin (see text).