Okay, let's tackle this question about winging of the scapula. The question is asking which nerve injury causes this condition. The correct answer is the long thoracic nerve. Let me break down the core concept first.

Winging of the scapula happens when the serratus anterior muscle isn't functioning properly. That muscle is innervated by the long thoracic nerve. If this nerve is damaged, the muscle can't hold the scapula against the ribcage, causing it to wing out.

Now, why is the correct answer right? The long thoracic nerve provides motor innervation to the serratus anterior. When injured, the muscle becomes weak or paralyzed, leading to the scapula protruding when the arm is raised. This is a classic sign of long thoracic nerve palsy.

For the incorrect options: Option A might be the axillary nerve, which affects the deltoid and teres minor. Option B could be the thoracodorsal nerve, which innervates the latissimus dorsi. Option C might be the suprascapular nerve, which affects the supraspinatus and infraspinatus. Each of these nerves controls different muscles, so their injury wouldn't cause scapular winging.

The clinical pearl here is to remember that the serratus anterior is the key muscle involved in scapular winging, and it's innervated by the long thoracic nerve. A mnemonic could be "Long Thoracic for Serratus Anterior – LTS for LTS!"

Putting it all together, the correct answer is the long thoracic nerve. I need to make sure each section is concise and fits within the character limit. Let me check the formatting and ensure all sections are covered properly.

**Core Concept**
Scapular winging occurs when the serratus anterior muscle is weakened or paralyzed, leading to loss of scapular stabilization against the thoracic wall. The *long thoracic nerve* (C5-C7) is the primary motor nerve to this muscle. Damage to this nerve disrupts normal scapulohumeral rhythm.

**Why the Correct Answer is Right**
The **long thoracic nerve** innervates the serratus anterior, which protracts and stabilizes the scapula against the ribcage. Injury (e.g., from trauma, iatrogenic compression, or brachial plexopathy) causes the scapula to protrude ("wing") during arm elevation. This is a hallmark clinical sign of long thoracic nerve palsy.

**Why Each Wrong Option is Incorrect**
**Option A:** Axillary nerve innervates the deltoid and teres minor; injury causes shoulder abduction weakness and "square-shoulder" deformity.
**Option B:** Thoracodorsal nerve supplies the latissimus dorsi; injury impairs shoulder extension but does not cause scapular winging.
**Option C:** Suprascapular nerve innervates the supraspinatus and infraspinatus; injury leads to shoulder abduction/external rotation deficits, not scapular winging.

**Clinical Pearl / High-Yield Fact**
Remember: "Serratus anterior = Long thoracic nerve" (LTN). On exam, ask the patient to push against resistance—winging becomes evident when the serratus anterior cannot stabilize the medial border of the

✓ Correct Answer: A. Long thoracic nerve