Final answer:
In anterolateral displacement of a supracondylar humerus fracture, the radial nerve is at risk, while an anteromedial displacement puts the median nerve and potentially the brachial artery at risk. Both types of displacement can compromise nerves responsible for sensation and muscle movement in the arm and hand.
Step-by-step explanation:
When considering a supracondylar humerus fracture where the proximal fracture fragment is displaced, the structures at risk for injury depend on the direction of the displacement. In the event of an anterolateral displacement, there is concern for injury to the radial nerve due to its proximity to the lateral aspect of the distal humerus. The radial nerve is responsible for extension of the wrist and fingers and sensory innervation to the posterior aspect of the arm and hand.
For an anteromedial displacement of the proximal fracture fragment, the primary structure at risk is the median nerve. The median nerve travels medial to the humerus and is responsible for flexion of the wrist and fingers, as well as sensation to the palmar aspect of the hand. Additionally, the brachial artery, which runs medial to the humerus, can also be compromised leading to potential issues with forearm perfusion.
It's important to note that with any supracondylar fracture, there's also a risk of injury to the ulnar nerve, especially if there is medial displacement, as it runs in close proximity to the medial epicondyle.