Final answer:
Kehr's sign is referred pain felt in the left shoulder due to diaphragmatic irritation, commonly caused by a ruptured spleen. This phenomenon occurs because the brain misinterprets signals due to shared nerve pathways between the diaphragm and the shoulder.
Step-by-step explanation:
Understanding Kehr's Sign
Referred pain to the left shoulder caused by diaphragmatic irritation, which in turn is caused by the presence of blood and may indicate a spleen injury, is known as Kehr's sign. The presence of referred pain is when the conscious perception of visceral sensation is projected to a different part of the body. With referred pain, strong visceral sensations of an affected organ are felt in unexpected areas.
In the case of Kehr's sign, the rupture of the spleen leads to blood accumulating near the diaphragm, which is sensed as pain in the left shoulder due to the shared nerve pathways. This is because the visceral and somatosensory fibers connected to the spleen and shoulder respectively enter the spinal cord at the same level, causing the brain to misinterpret the origin of the distress.