This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Shoulder and arm injuries, Subject name: Orthopaedics
[{'content': 'Nerve commonly involved in fracture distal shaft of the Humerus is ? \nSelect and explain. \nA. Radial nerve, B. Medial nerve, C. Ulnar nerve, D. Circumflex brachial nerve', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Up to 18% of humeral shaft fracture is an associated radial nerve palsy, but may occur more commonly in distal third fractures. Radial nerve is commonly at risk if the fracture is at the junction of mid and distal thirds of the humeral shaft and paicularly if fracture is associated with lateral displacement of distal fragment At this point the radial nerve emerges from the spiral groove and is tethered as it pierces the intermuscular septum; It cannot yeild to the lateral displacement of the distal fragment, and is therefore frequently damaged; ref : maheswari 9th ed', 'role': 'assistant'}]