You are in the causlity when a student, is brought in with a shoulder injury sustained while playing football. In comparing the symmetry of his two shoulders, you notice a marked elevation of the distal end of his clavicle with respect to the acromion on the injured side. X-ray examination reveals a grade III shoulder separation. In order for this to have occurred, which ligament must be torn?

**Core Concept**
The question tests the understanding of shoulder anatomy and the specific ligament responsible for shoulder stability, particularly in the context of a grade III shoulder separation. A grade III shoulder separation involves a significant displacement of the clavicle from the acromion, indicating a severe injury to the ligaments that connect these bones.

**Why the Correct Answer is Right**
A grade III shoulder separation occurs due to the tearing of the acromioclavicular (AC) ligament, which is a strong ligament that connects the acromion process of the scapula to the clavicle. The AC ligament plays a crucial role in stabilizing the shoulder joint and preventing excessive movement between the clavicle and the scapula. In a grade III shoulder separation, the AC ligament is completely torn, allowing for a significant displacement of the clavicle from the acromion.

**Why Each Wrong Option is Incorrect**
* **Option A:** The coracoclavicular ligament is also involved in shoulder stability, but it is not the primary ligament torn in a grade III shoulder separation. The coracoclavicular ligament connects the clavicle to the coracoid process of the scapula.
* **Option B:** The sternoclavicular joint is a separate joint that connects the clavicle to the sternum, and injuries to this joint are not directly related to a grade III shoulder separation.
* **Option D:** The rotator cuff muscles and tendons are not directly involved in the ligamentous stability of the shoulder joint in the context of a grade III shoulder separation.

**Clinical Pearl / High-Yield Fact**
In a grade III shoulder separation, it is essential to assess the integrity of the AC ligament and the coracoclavicular ligament to determine the severity of the injury and guide treatment.

**Correct Answer:** C.

✓ Correct Answer: B. Coracoclavicular