This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Upper limb, Subject name: Anatomy
[{'content': "Erb's palsy occurs due to involvement of \nSelect and explain. \nA. Upper trunk of brachial plexus, B. Middle trunk of brachial plexus, C. Medial cord of brachial plexus, D. Lateral trunk of brachial plexus", 'role': 'user'}, {'content': "Answer: A \nExplanation: ERB'S PARALYSIS:- upper plexus injury.Caused by forceful widening of the angle between the head and shoulder which may occur by traction of arm during the bih of a child or by fall on the shoulder.Involves upper trunk - C5, C6 roots. Leads to typical deformity in the limb- policeman's tip hand/ poer's tip hand. The arm hangs by the side,adducted and medially rotated, forearm is extended and pronated. 1. Adduction of arm due to deltoid paralysis.2. Medial rotation of arm-paralysis of supraspinatus, infraspinatus and teres minor.3. Extension of elbow- paralysis of biceps brachii4. Pronation of forearm- paralysis of biceps brachi5. Loss of sensation over outer aspect of arm due to C6 spinal nerve involvement.{Reference: vishram singh, page no. 62}", 'role': 'assistant'}]