Question

A 19 year old boy fell from a motorbike onto his shoulder. The doctor diagnosed him as a case of Erb's paralysis. All of the following signs and symptoms will be observed except:

• A. Loss of abduction at shoulder joint
• B. Loss of lateral rotation
• C. Loss of pronation at radioulnar joint
• D. Loss of flexion at elbow joint

Hint:

Erb's palsy hits C5, C6; work out which movements those roots control, then find the one movement that is NOT one of them.

Answer 1

The Correct Option is C

Step 1: Recall which nerve roots are hurt in Erb's palsy.
Erb's palsy follows a forceful widening of the angle between the neck and shoulder, exactly what happens when a person falls onto the point of the shoulder. This stretches and injures the upper trunk of the brachial plexus, formed by nerve roots C5 and C6.

Step 2: List the muscles supplied by C5, C6.
C5 and C6 supply deltoid and supraspinatus (abduction), infraspinatus and teres minor (lateral rotation), and biceps brachii and brachialis (elbow flexion and forearm supination).

Step 3: Work out which movements are lost.
With these muscles weak or paralysed, the boy loses shoulder abduction (deltoid and supraspinatus gone), loses lateral rotation (infraspinatus and teres minor gone), and loses elbow flexion (biceps and brachialis gone). This matches options (A), (B), and (D), so all three are genuinely seen in Erb's palsy.

Step 4: Work out what happens to pronation and supination.
Biceps brachii is the main supinator of the forearm. When it is paralysed, the forearm loses supination, not pronation. Pronator teres, supplied mainly through C6, C7 by the median nerve, is largely spared, so pronation still works. Because the supinators are weak and cannot oppose the pull of intact pronators, the limb classically falls into a pronated posture, this is part of the well known "waiter's tip" position, but the actual deficit is loss of supination, not loss of pronation.

Step 5: Final conclusion.
Loss of pronation is not a feature of Erb's palsy, since pronation is preserved and it is supination that is lost.
\[ \boxed{\text{Loss of pronation at radioulnar joint}} \]