**Core Concept**
Kehr's sign is a clinical manifestation of referred pain that occurs when there is bleeding in the spleen (splenic rupture) or other abdominal organs. The pain is referred to the left shoulder due to the activation of phrenic nerve C fibers, which are stimulated by the irritation of the diaphragm caused by blood in the abdominal cavity.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of referred pain in the context of splenic rupture. When there is bleeding in the spleen, the blood irritates the diaphragm, leading to the activation of phrenic nerve C fibers. These fibers transmit pain signals to the brain, which interprets the pain as coming from the left shoulder region. This referred pain is a result of the convergence of visceral and somatic afferent fibers in the spinal cord.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because Kehr's sign is specifically related to splenic rupture or other abdominal organ bleeding, not to other conditions such as pulmonary embolism or myocardial infarction.
* **Option B:** This option is incorrect because Kehr's sign is a clinical manifestation of referred pain, not a diagnostic criterion for a specific disease.
* **Option C:** This option is incorrect because Kehr's sign is related to the left shoulder, not the right shoulder.

**Clinical Pearl / High-Yield Fact**
Kehr's sign is an important clinical clue for diagnosing splenic rupture or other abdominal organ bleeding. Remember that referred pain to the left shoulder can be a sign of internal bleeding, and prompt evaluation and management are essential to prevent further complications.

**Correct Answer:** D.