Erb-Duchenne paralysis occurs by lesion to brachial plexus at the level of
**Erb-Duchenne Paralysis**
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**Core Concept**
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Erb-Duchenne paralysis is a type of brachial plexus injury that affects the upper trunk of the brachial plexus, resulting in weakness or paralysis of the muscles innervated by the C5 and C6 nerve roots. This condition is characterized by the involvement of the musculocutaneous nerve (C5-C7), axillary nerve (C5-C6), and suprascapular nerve (C5-C6).
**Why the Correct Answer is Right**
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The correct level of lesion for Erb-Duchenne paralysis is typically at the level of the **upper trunk of the brachial plexus**, where the C5 and C6 nerve roots merge to form the superior trunk. This level of injury results in the characteristic clinical features of Erb-Duchenne paralysis, including weakness or paralysis of the shoulder abduction and external rotation, elbow flexion, and forearm supination.
**Why Each Wrong Option is Incorrect**
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* **Option A:** Lesion at the level of the lower trunk of the brachial plexus (C8-T1) would result in a different pattern of weakness, including paralysis of the intrinsic muscles of the hand and wrist.
* **Option B:** Lesion at the level of the middle trunk of the brachial plexus (C7) would result in weakness of the muscles innervated by the C7 nerve root, including the muscles of the forearm and wrist.
* **Option D:** Lesion at the level of the roots of the brachial plexus (C5-T1) would result in a more extensive pattern of weakness, including paralysis of the muscles of the arm, forearm, and hand.
**Clinical Pearl / High-Yield Fact**
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The **"waiter's tip" sign** is a classic clinical feature of Erb-Duchenne paralysis, where the patient's arm hangs in a position that resembles a waiter's tip, due to weakness of the muscles of the shoulder and elbow.
**Correct Answer: C. Upper trunk of the brachial plexus.**