A 54 year old man with a long history of smoking is diagnosed with squamous cell carcinoma of the larynx. During the course of a radical neck dissection to remove the tumor and regional lymph nodes, the spinal accessory nerve is severed. As a result, the man would most likely have the greatest difficulty in?

**Core Concept**
The spinal accessory nerve (cranial nerve XI) is a motor nerve that innervates the sternocleidomastoid and trapezius muscles. It plays a crucial role in shoulder movement and stability. Damage to this nerve can lead to significant impairment in shoulder function.

**Why the Correct Answer is Right**
The spinal accessory nerve is responsible for the innervation of the trapezius muscle, which is essential for shoulder elevation, depression, and rotation. When the trapezius muscle is paralyzed, the individual would experience difficulty in performing activities that require shoulder abduction, such as reaching overhead or carrying heavy objects. The trapezius muscle also helps in stabilizing the scapula, and its paralysis can lead to scapular winging, which can further compromise shoulder function.

**Why Each Wrong Option is Incorrect**
**Option A:**
Damage to the spinal accessory nerve would not primarily affect the sternocleidomastoid muscle, which is responsible for rotating the head and neck, rather than shoulder movement.

**Option B:**
While the trapezius muscle does contribute to scapular rotation, the primary function of the spinal accessory nerve is to innervate this muscle, and its paralysis would not primarily affect scapular rotation.

**Option C:**
The spinal accessory nerve does not innervate the muscles of the arm or forearm, and its paralysis would not primarily affect hand function.

**Clinical Pearl / High-Yield Fact**
The spinal accessory nerve can be at risk during neck dissections, particularly when the surgeon is retracting the sternocleidomastoid muscle. It is essential to identify and preserve this nerve to prevent postoperative shoulder dysfunction.

**Correct Answer:** C. Hand function is not primarily affected by the paralysis of the trapezius muscle, which is innervated by the spinal accessory nerve.

✓ Correct Answer: C. Elevating the point of the shoulder (shrugging)